WO2011134691A2

WO2011134691A2 - Method for producing a metal-wrap-through-solar cell and a metal-wrap-through-solar cell produced according to said method

Info

Publication number: WO2011134691A2
Application number: PCT/EP2011/052501
Authority: WO
Inventors: Hans-Joachim Krokoszinski
Original assignee: Robert Bosch Gmbh
Priority date: 2010-04-26
Filing date: 2011-02-21
Publication date: 2011-11-03
Also published as: DE102010028187A1; EP2564433A2; WO2011134691A3

Abstract

The invention relates to a method for producing a metal-wrap-through-solar cell consisting of a p-doped or n-doped silicon substrate (1), which has a first main surface (2) that serves as a light incidence side when used and a second main surface (3) that serves as the back. Said method consists of the following steps: a thin layer (5) which is essentially made of aluminium is applied to the second main surface (3), the aluminium thin layer (5) is removed from parts of the second main surface (3) for forming hole areas (9) having a first diameter (d1) in which the silicon substrate (1) is released, a dielectric, gas-forming paste (11) is applied to and dried on the aluminium thin layer (5) for covering the thin layer (5) and parts of the silicon substrate (1), resulting in the hole areas (9) being reduced in size to a second diameter (d2), forming interconnecting holes (10) through the silicon substrate (1) in the hole areas (9), in particular by means of a laser (13), the paste (11) on the second main surface (3) is heated and/or sintered (11), in particular to temperatures over approximately 577 °C, for producing an aluminium doping layer (6) in the second main surface (3), and the glass layer (12) and an aluminium silicon eutectic layer formed from heating and/or sintering is removed from the second main surface (3) thus releasing the aluminium doping layer (6).

Description

description

title

A method of making a metal wrap Throuqh solar cell and a metal wrap Throuqh solar cell made by this method

The present invention relates to a method for producing a metal wrap-through solar cell and to a metal wrap-through solar cell produced by this method. State of the art

Silicon solar cells, also known as metal wrap-through (MWT) cells, have so far been provided with an all-over screen-printed metallization for mirroring and current collection on the back. This backside metallization typically consists of aluminum-based thick-film paste printed over a large area between the silver-based solder pads of the base distributed over the back surface and the solder pads of the back emitter regions terminated by laser drilled silver filled holes (vias). the front metal contact rails / Fingergrid are connected, spaced at a distance of about 0.5 mm - 0.7 mm (see F. Clement, IEEE

Conference, Philadelphia (USA), June 2009). When sintering above 800 ° C, the aluminum alloyed by forming the low-melting (577 ° C) AlSi eutectic and recrystallization to the semiconductor surface, thereby compensating the existing n ⁺ doping from the previously all-around phosphorus diffusion to a highly p-doped ( p ⁺ -) doping via (see F.

Huster, 20th European Photovoltaic Solar Energy Conference, 6-10 June 2005, Barcelona, Spain). Since the base doping p is hitherto, the aluminum-doped recrystallized surface layer forms a p ⁺ -BSF (Back Surface Field) with a p ⁺ p junction (so-called high-low transition). Then, "edge isolation" must be performed in the gap between emitter solder pads and the surrounding sintered aluminum layer, typically by laser dicing (see F. Clement, IEEE Conference, Philadelphia (USA), June 2009).

In another method, the MWT cell is made of n-doped material. The backside p ⁺ emitter is generated via aluminum diffusion. The disadvantage of this doping method is that for the diffusion of

Aluminum in silicon required high temperature of 1100 ° C ± 50 ° C, because it breaks down (including through the formation of aluminum-oxygen complexes) the life of the minority carriers (holes) of the n-type silicon wafers strong.

The alternative for aluminum diffusion, boron diffusion, also takes place at relatively high temperatures. It is therefore also disadvantageous because of the high thermal budget and the associated costs and risks.

A disadvantage of the previously known method is that the printed

40 μm (after sintering) must be thick in order to obtain sufficiently deep alloy formation or aluminum doping depth. Due to the bimetallic effect between it and the silicon wafer, a reduction in the wafer thickness below the hitherto typical 180 μιτι leads to an intolerable wafer bending (so-called Bow). Due to the necessary thickness of the silicon wafer and the amount of silicon that is therefore required, high costs are incurred for the solar cell.

The silkscreen metallization of the back has an imperfect texture

Reflection factor of only 65% for the long-wavelength sunlight, which penetrate to the back. A more efficient silvering of> 90% would increase the optical path length of the incident light and thus the generation of electron-hole pairs (ie, the current) inside the cell. Thus, a significant efficiency gain can be achieved. A metallic surface, both an emitter and one

Back Surface Fields (BSF), despite the field passivation by high doping has a large charge carrier recombination speed. In order to enable better passivation of the aluminum-doped surface of the back surface, the thick aluminum screen printing layer required as doping source and the AISi eutectic layer formed between it and the semiconductor surface must be etched off. For this purpose, a large amount of hydrochloric acid is necessary due to the thickness of the layers to be etched in the previously known method, which is a major disposal problem. In addition, a laser ditch must surround the back emitter solder pads to the back emitter solder pads of the surrounding them

Isolate aluminum surfaces. If the back emitter solder pads have the shape of long busbars, this creates the risk of mechanical weakening by so-called "predetermined breaking points", which significantly increases the breakage rate.

Disclosure of the invention

The present invention relates to a method for producing a metal wrap-through solar cell from a p-doped or n-doped and saw damage etched silicon substrate, which has a first main surface serving as a light incident side in use and a second main surface serving as a back side, comprising the following steps:

Depositing a thin film substantially comprising aluminum on the second major surface, removing the aluminum thin film from portions of the second major surface to form first diameter (dl) hole areas in which the silicon substrate is exposed, depositing and drying a dielectric , glass-forming paste on the aluminum thin film for covering the thin film and parts of the silicon substrate in the hole regions, whereby the hole regions are reduced to a second diameter (d2), forming through-holes through the silicon substrate in the hole regions, in particular by means a laser, heating and / or sintering the paste on the second main surface, in particular at temperatures above 800 ° C, to produce an aluminum Doping layer in the second main surface with simultaneous doping of the first main surface with phosphorus, and removal of the glass layer resulting from the heating and / or sintering and an aluminum-silicon eutetic layer resulting from the heating and / or sintering from the second main surface, whereby the aluminum Doping layer is exposed.

An advantage of this is that a metal wrap-through solar cell with an aluminum doping layer on the second main surface is produced in a technically simple manner. In addition, it is advantageous that the aluminum layer is applied in direct contact with the second main surface, thereby melting the eutectic point, the entire layer amount of aluminum directly, ie undelayed or unhindered, are consumed for melting. In addition, the structuring of the aluminum layer, ie the exposure of surrounding areas of the via holes, ensures that the n + doping does not have to overcompensate the p + doping if these areas are doped with a different polarity. In addition, the covering of the aluminum layer with a glass paste or glass layer ensures that when the aluminum-silicon eutectic melts, the melt is not substantially exposed at any point and thus the eutectic layer does not run to drip even in a vertical position in a high-temperature furnace. splashed or oxidized. The fact that the glass cover is only needed temporarily, it can be made significantly thinner. In addition, due to its lower coefficient of expansion, which is similar to that of silicon, the glass cover largely does not distort the silicon substrate. This increases the efficiency of the solar cell and the thickness of the silicon substrate can be significantly reduced, which saves considerable costs. In addition, it is possible to dispense with isolation trenches around the plated-through holes, which significantly increases the stability of the silicon substrate. The heating and / or sintering may take place at a temperature of at least 800 ° C. This ensures that the aluminum doping proceeds along with the phosphorus doping of the first major surface. In the method, the paste can be applied by means of printing, in particular by screen printing. This further reduces the cost of the process. On the other hand, the areas around the through-hole to be drilled later with a second diameter d2 can be left free.

In one embodiment of the method, prior to the application of the paste to the second main surface, a thin dielectric layer, in particular an oxide and / or a nitride, is furthermore applied to the aluminum thin layer to prevent oxidation of the aluminum of the aluminum thin layer in air, and removing portions of the dielectric layer from the second major surface to form the first diameter (d1) hole regions. This ensures that the aluminum thin film does not oxidize, which could negatively affect the production of an aluminum eutectic or the aluminum doping layer.

In the method, further, after drilling the holes by laser and before removing the glass layer, the first major surface, the walls of the via holes, and the hole areas are anisotropically etched, particularly with potassium hydroxide and isopropanol, to form a texture. The texturing allows an improved coupling of the incident

Sunlight and thus a higher efficiency and easier application of additional layers.

In a further embodiment of the method, the first major surface is further doped by diffusion of phosphorus and by driving in the phosphor during heating and / or sintering of the glass forming paste to produce a phosphorus doping layer in the first major surface, and a phosphosilicate glass layer resulting from the doping and subsequent driving away. The advantage of this is that in a technically simple manner, a phosphorus doping layer is produced in the first main surface. Since the glass-forming paste is sintered during the phosphorus diffusion, an additional temperature step is saved.

The process may further comprise, after removal of the phosphosilicate glass simply a passivation layer and / or anti-reflection layer, in particular comprising SiN or SiN / Si0 ₂ , are applied to the first main surface. An advantage of this is that less light is reflected by an anti-reflection layer and the recombination of charge carriers and the penetration of foreign atoms is reduced by a passivation layer. Both increase the efficiency of the solar cell and extend the life of the solar cell.

In one embodiment of the method, further, after exposing the aluminum doping layer to the walls of the via holes and the hole areas of the second main surface to produce a metal layer, a silver-containing paste is screen-printed and dried.

As a result, an electrical connection between the first main surface and the second main surface is technically easily produced. In another embodiment, after applying and drying the silver-containing metal contact-forming paste paste, a metal paste is further applied to the first major surface, the metal paste in contact with one or more via holes, and the metal paste on the first major surface and the silver-containing paste in the first Through-hole and sintered together in the hole areas of the second main surface and / or heated. One advantage of this is that technically simple metal contact tracks are formed on the first main surface and an additional step is saved by the common sintering and / or heating of the metal paste on the first main surface and the silver-containing paste.

The metal paste can be applied by screen printing, aerosol printing or dispensing. This inexpensive method of applying the metal paste ensures a uniform thickness of the metal paste over the entire first major surface.

In a further embodiment of the method, furthermore, after the exposure of the aluminum doping layer, a passivation layer is applied to the second main surface and parts of the passivation layer are applied to the second main surface second main surface for producing local openings for contacting the silicon substrate and for generating the hole areas around the through-holes having a third diameter (d3), which has a value between dl and d2 removed, in particular by means of etching or

Laser ablation. The passivation layer and the aluminum layer form a significantly better infrared light mirror than the porous AI layer according to the prior art. As a result, a higher power output of the solar cell is achieved.

In the method, further, after removing portions of the passivation layer, a further aluminum layer and optionally a nickel layer may be applied to the second main surface for contacting the silicon substrate in the hole areas of the second main surface, in particular by sputtering or vapor deposition, and parts of the other Aluminum layer and optional nickel layer are removed from the second main surface to expose the hole areas around the first diameter (dl) via holes, particularly by etching. The passivation layer reduces the recombination of charge carriers, thereby increasing the efficiency of the solar cell. It is also advantageous that in a technically simple manner, the second main surface of the silicon substrate is contacted by the further aluminum layer. In addition, the open circuit voltage can be increased. The optional nickel layer makes it much easier to apply further layers to the second main surface. In another embodiment of the method, further, after exposing the aluminum doping layer, a thin dielectric layer is deposited on the second major surface, portions of the dielectric layer are exposed from the second major surface to expose third diameter (d3) hole areas around the via holes and Forming solder contact surface openings having a fourth diameter (d4) removed, and comprising a metal alloy, in particular nickel, silver, copper and / or tin, on the metal contact tracks of the first main surface and the solder contact surface openings of the second main surface for reinforcing the metal contact tracks and / / or solder pad openings galvanic and / or chemically applied. As a result, in a technically simple way and

We have fabricated solder pad openings that can be easily contacted by soldering to electrically contact the second major surface of the silicon substrate. The present invention likewise provides a metal wrap-through solar cell made of a p-doped or n-doped silicon substrate, which has a first main surface serving as a light incident side in use and a second main surface serving as a back side, with through-contacting holes the silicon substrate for connecting the second main surface to the first main surface, wherein the second main surface has an aluminum doping layer and the silicon substrate has a thickness of less than about 200 μιτι, in particular less than about 180 μιτι having. The advantage of this metal wrap-through solar cell is that, because of the small thickness, less silicon is required for the silicon substrate, which saves costs.

drawings

Further advantages and expediencies of the invention are illustrated by the drawings and explained in the following description.

It should be noted that the drawings have only descriptive character and are not intended to limit the invention in any way. 1 to 19 are cross-sectional views of a silicon substrate according to various steps of a method according to the invention.

In the following description, the same reference numerals will be used for the same and like parts.

1 shows a cross-sectional view of a silicon substrate 1. The silicon substrate 1 is n-doped or p-doped. The silicon substrate 1 has a first main surface 2, which serves as a light incident side in use, and a second main surface 3 serving as a back surface in use. The silicon 4 of the silicon substrate 1 may be monocrystalline or multicrystalline. The surfaces are already acid-etched.

In a first method step, a very pure, thin aluminum layer 5 is applied to the second main surface 3. An aluminum layer which is as pure as possible is to be understood as meaning a layer which essentially comprises only aluminum. The application can be done for example by vapor deposition or sputtering. The aluminum thin film 5 substantially covers the second main surface 3 to as small as possible

Distance to the edge of the silicon substrate 1. The distance to the edge of the silicon substrate 1 may also be equal to zero. The layer thickness of the aluminum thin layer 5 is selected with regard to the depth of an aluminum doping layer 6 produced during sintering or heating in a later method step. Depending on the doping of the silicon substrate 1, the aluminum doping layer 6 serves as an emitter or as a back-surface field. The depth or thickness of the aluminum doping layer 6 produced in a later method step is preferably between 1 μιτι and 10 μιτι.

FIG. 2 shows a cross-sectional view of the silicon substrate 1 after a further, optional method step, in which a thin dielectric

Layer 7 is applied to the aluminum thin film 5 in order to avoid oxidation of the aluminum in air. The thin dielectric layer 7 can be applied in the same vapor deposition or sputtering system in which the aluminum thin film 5 is applied. The thin dielectric

Layer 7 preferably comprises an oxide and / or nitride.

FIG. 3 shows the silicon substrate 1 after a further method step. A masking layer 8 is applied to the second main surface 3 of the silicon substrate 1, which exposes hole regions 9 with a first diameter (d1), in which the through-contacting holes 10 of the metal wrap-through solar cell are formed in a later method step should be. Now, with a known from the prior art method of Schichtstrukturierung such. Etch paste printing, masked wet chemical etch, or masked dry etch, portions of the thin dielectric layer 7, so that the aluminum thin film 5 is exposed in the regions 9 left clear of the masking layer 8. In these exposed hole areas 9, the through-holes 10 or vias of the metal wrap-through (MWT) cell and the surrounding soldering surfaces are formed later. The diameter of these hole areas 9 is after this step dl.

In the next process step, the aluminum thin film 5 in the hole regions 9 is etched away (see FIG. 4), whereby the silicon 4 of the silicon substrate 1 is exposed in the hole regions 9, and then the masking layer 8 is removed again from the second main surface 3. Alternatively, when the optional thin dielectric layer 7 is applied and opened by laser ablation, the masking layer 8 may be omitted prior to this process step because the dielectric layer 7 protects the aluminum thin film 5 during the etching process. Now, at one or more locations of the second main surface 3, the silicon 4 of the silicon substrate 1 are exposed in an area with the first diameter (d1).

The silicon substrate 1 after a further method step is shown in FIG. 5. In this process step, a dielectric glass-forming paste 11 is applied to the aluminum thin film 7 and parts of the silicon 4 of the silicon substrate 1 in the hole regions 9, so that the width of the hole regions 9 from the first width dl to the one width (d2 ), where d2 is only slightly smaller than dl. This application is preferably done by screen printing. This covering of the aluminum thin film 5 by a dielectric, glass-forming paste 11 is only temporary during the process and is removed again in a later process step after the doping of the second main surface 3. Therefore, their thickness can be selected as thin as possible, preferably between 10 μιτι to 12 pm. Due to the smaller thickness, less acid is required to dissolve or remove the glass layer 12 formed from the paste 11 in a later process step.

Thus, the load of the etching bath, usually hydrofluoric acid, with material aufzulösendem at least a factor of 4 less than the load of the hydrochloric acid bath in the removal of a 40 μιτι thick screen-printed aluminum layer according to the previously known methods.

In the next method step, via holes 10 in the silicon substrate 1 are produced by a method known from the prior art. Preferably, the number of holes is 60 to 100 holes per silicon substrate 1. The via holes 10 connect the second main surface 3 of the silicon substrate 1 to the first main surface 2. Preference is given to the via holes 9 by bombardment with a laser beam 13 from the second main surface 3 produced. Preferably, the diameter of the via holes 10 is between 70 μιτι and 120 μιτι and the diameter is slightly greater at the entrance to the second main surface 3 than at the exit on the first main surface 2. This step is shown in FIG.

FIG. 7 shows a cross-sectional view of the silicon substrate 1 after a further method step, in which a texturing is etched. The glass layer 12 or glass paste 11 according to the invention of the second main surface 3 essentially protects the second main surface 3 from etching, with the exception of the hole regions 9 surrounding the via holes 10. The texturing thus takes place on the first main surface 3, into which

Through holes 10 and walls of the via holes 10 and in the hole areas 9 with the second diameter (d2) on the second main surface. 3

Fig. 8 shows the step of phosphorus doping. In this process step, a standard phosphorus diffusion followed by a driving step. The phosphorus diffusion is preferably accomplished with POCl ₃ 14. In the driving step which proceeds above 800 ° C, the phosphorus is driven into the silicon substrate 1, and at the same time, under the glass layer 12 of the second main surface 3, the aluminum thin film 5 and the silicon 4 on the second main surface 3 form a liquid eutectic AlSi - phase. The thickness of the liquid layer depends on the currently prevailing temperature and thickness of the aluminum thin film 5 at any time. Upon cooling after the diffusion of the phosphorus and subsequent driving step above 800 ° C recrystallized below the eutectic Temperature (about 577 ° C), the aluminum-doped crystal layer from the inside out to a p ⁺ layer. This p ⁺ layer represents at an n-doped

Silicon substrate the emitter, and in the case of a p-doped silicon substrate, the back-surface field. Subsequently, the remaining eutectic melt solidifies in the form of the edge phases of the phase diagram to AlSi layer with granular structure. Preferably, the temperature during the driving step is less than 900 ° C. In the phosphorous doping, a phosphorus doping layer 15 is mainly formed in the first main surface 2, the walls of the via holes 10, and the exposed hole areas 9 of the second main surface 3. Alternatively, the glass paste 11 can be heated or sintered in a step independent of the phosphorus doping, preferably at temperatures above 800 ° C. and / or below 900 ° C., whereby an above-described processes underneath the glass layer 12 likewise produce an aluminum doping layer 6 in the second main surface 3 is formed.

After (simultaneous) doping of the first main surface 2 with phosphorus and the second main surface 3 with aluminum, all layers above these doping layers 15, 6 on the first main surface 2 and the second main surface 3 can now be removed. For this purpose, first the dielectric layers, ie the phosphorosilicate glass layer formed during the driving step and the glass layer 12 formed from the glass-forming paste 11, and then the AISi residual layers are etched off with hydrofluoric acid. The silicon substrate 1 after this process step is shown in FIG. 9. The silicon substrate 1 has two so-called p ⁺ -n ⁺ gaps 16 each between the aluminum doping layer 6 of the second main surface 3 and the part of the second main surface 3 having a phosphorus doping layer.

10 shows a cross-sectional view of the silicon substrate 1 after a further method step. In this method step, a passivation layer and / or antireflection coating (ARC) 17 is applied to the first main surface 2. In this application, the one passivation layer and / or antireflection layer 17 is also partially applied to the walls of the via holes 10. Although the walls of the Taktierungslöcher 10 and the back hole areas 9 were doped with phosphorus, they are in the standard processes for deposition of the passivation layer and / or anti-reflection layer 17 such as plasma Enhanced Chemical Vapor Deposition (PECVD) only imperfect with the passivation layer and / or anti-reflection layer 17 and Anti-reflection layer sequence covered. Therefore, for the metallization of the via holes 10 in the next process step, a special silver-containing paste is selected which contacts n ⁺ surfaces well, but does not penetrate the pn junction in p-doped materials (so-called shunting). In n-doped silicon substrates, the problem is less, since there is only one n ⁺ -n transition, which can not be shunted.

FIG. 11 shows the silicon substrate 1 after this process step in which, by printing, sucking and drying the silver-containing paste, metallization of the walls of the via holes 10 and the back hole regions 9 has been made, that is. H. a metal layer 18 has been applied to this.

Subsequently, with a known from the prior art method, such. As screen printing, aerosol printing, dispensing, a metal paste, preferably a silver paste applied to the first main surface 2. This metal paste forms metal contact tracks 19, so-called narrow fingers. All of the metal contact pads 19 and fingers, respectively, have contact with a plurality of via holes 10 provided with a metal layer 18 to conduct the current to the contacts on the second main surface 3. Subsequently, the metal paste of the first main surface 2 is simultaneously sintered together with the silver paste of the second main surface 3, for example, in a furnace process. The silicon substrate 1 after this process step is shown in FIG. 12. 13 shows the silicon substrate 1 after a further method step, in which a passivation layer 20 suitable for p ⁺ doping has preferably been applied to the second main surface 3 by means of the PECVD method. This happens, for example, after a short treatment with hydrogen fluoride HF, the so-called HF dip. Subsequently, this passivation layer 20 with one of the known methods (laser ablation, etching paste, masked wet chemical etching or ion etching) at many points 21 of the second main surface 3 locally opened, ie, a so-called PERC structure is prepared. In this case, the hole regions 9 are also opened around the through-contacting holes 10 with the third diameter (d3), which lies between d1 and d2. This is shown in FIG.

Subsequently, the entire second main surface 3 is covered with a sufficiently thick further aluminum layer 22. The application of this further aluminum layer 22 may, for example, by a PVD method, for. B.

Sputtering or vapor deposition, done. The further aluminum layer 22 directly touches the second main surface 3 of the silicon substrate 1 in the exposed hole regions 9 of the passivation layer 20 and rests on the passivation layer 20 in all other regions of the second main surface 3. This is shown in FIG. Advantageously, a thin nickel-containing layer is deposited on the further aluminum layer 22 in the same PVD system in order to be able to deposit a solderable layer on it in the bus bar / busbar regions or solder contact surface regions in a later process step by a chemical and / or galvanic process to facilitate.

16 shows a cross-sectional view of the silicon substrate 1 after another masked etching process. A masking layer 8 has been applied to the second main surface 3 leaving a first diameter (dl) area around the via holes 10. During the etching, a hole region 9 with the first diameter (d 1) around each through-connection hole 10 is freed from the further aluminum layer 22 and the optional nickel layer. The first diameter (d1) corresponds to the opening width in the aluminum doping layer 6 of the second main surface 3. In order to limit the gain, ie the deposition of solderable layers, to the solder contact area regions, in a further method step a thin dielectric layer 23 is applied to the entire second Main surface 3 is deposited (see Fig. 17) and then removed portions of the thin dielectric layer 23 to Lotötflächen areas 24 with the fourth diameter (d4) and hole portions 9 of the width d3 and the third diameter (d3) to the via holes 10 to produce. This can be done with one of the known methods, such as. B. laser ablation,

Etching paste, masked wet chemical etching or ion etching, done. In FIGS. 18a and 18b, it is shown that a masking layer 8 has been applied to the second main surface, the hole regions 9 to the third

Diameter (d3) around the via holes 10 and Lötkontaktbereiche 24 with the fourth diameter (d4) leaves free. After removing the thin dielectric layer 7, the masking layer 8 is removed again.

Finally, in a galvanic or chemical deposition process, the metal contact tracks 19 or fingers on the first main surface 2 and the solder contact surfaces 24 of both polarities on the second main surface 3 are each reinforced with a solderable layer sequence 25 or 26 (see FIG. 19). The solderable layer sequences preferably comprise a suitable combination of the metals nickel, silver, copper and tin.

It should be pointed out at this juncture that all the above-described steps of the method taken alone and in any combination, in particular the details shown in the drawings, are claimed to be essential to the invention. Variations thereof are familiar to the person skilled in the art.

Incidentally, the embodiment of the invention is not limited to the above-described examples and emphasized aspects, but only by the scope of the appended claims.

Claims

Expectations

1. Process for producing a metal wrap-through solar cell

a p-doped or n-doped and saw-damage-etched silicon substrate (1), which has a first main surface (2) which serves as the light incidence side in the use state and a second main surface (3) which serves as the back, comprising the following steps:

- applying a thin layer (5), which essentially comprises aluminum, to the second main surface (3), - removing the aluminum thin layer (5) from parts of the second

Main surface (3) for forming hole areas (9) with a first diameter (dl), in which the silicon substrate (1) is exposed, - applying and drying a dielectric, glass-forming

Paste (11) on the aluminum thin film (5) to cover the thin film

(5) and parts of the silicon substrate (1) in the hole areas (9), whereby the hole areas (9) are reduced to a second diameter (d2),

- Forming through-holes (10) through the silicon substrate (1) in the hole areas (9), in particular by means of a laser (13), - Heating and/or sintering the paste (11) on the second main surface (3), in particular at temperatures above approximately 577 ° C, to produce an aluminum doping layer (6) in the second main surface (3), and - Removing the glass layer (12) formed during the heating and/or sintering and an aluminum-silicon euticum layer formed during the heating and/or sintering from the second main surface (3), thereby forming the aluminum doping layer

(6) is exposed.

A method according to claim 1, wherein the heating and/or sintering takes place at a temperature of at least 800°C.

Method according to one of the preceding claims, wherein the paste (11) is applied by means of printing, in particular by means of screen printing.

Method according to one of the preceding claims, further comprising before applying the paste (11) to the second main surface (3)

- a thin dielectric layer (7), in particular comprising an oxide and/or a nitride, is applied to the aluminum thin layer (5) in order to avoid oxidation of the aluminum of the aluminum thin layer (5) in air, and

- Parts of the dielectric layer (7) are removed from the second main surface (3) to form the hole areas (9) with the first diameter (dl).

Method according to one of the preceding claims, further comprising etching the first main surface (2), walls of the via holes (10) and the hole regions (9), in particular with potassium hydroxide and isopropanol, to form a texturing before removing the glass layer.

A method according to any one of the preceding claims, further comprising the first major surface (2) by diffusion of phosphorus and by driving the phosphorus during heating and/or sintering of the glass-forming paste (11) to produce a Phosphorus doping layer (15) is doped in the first main surface (2) and

- a phosphosilicate glass layer created by the doping and subsequent driving is removed.

7. The method according to claim 6, wherein further after removing the phosphosilicate glass layer, a passivation layer and / or anti-reflection layer (17), in particular comprising SiN or SiN / SiO ₂ , is applied to the first main surface (2).

8. The method according to any one of the preceding claims, further comprising, after exposing the aluminum doping layer (6) on the walls of the via holes (10) and the hole regions (9) of the second main surface (3), a silver-containing metal layer (18). Paste is applied using screen printing and dried.

9. The method of claim 8, further comprising after application and

Drying the silver-containing paste

- To produce metal contact tracks, a metal paste (19) is applied to the first main surface (2), the metal paste being in contact with one or more plated-through holes (10), and

- the metal paste (19) on the first main surface (2) and the silver-containing paste in the plated-through holes (10) and in the hole areas (9) of the second main surface (3) are sintered and / or heated together.

10. The method according to claim 9, wherein the metal paste (19) by means

Screen printing, aerosol printing or dispensing processes are applied.

11. The method according to any one of the preceding claims, further comprising exposing the aluminum doping layer (6) - a passivation layer (20) is applied to the second main surface (3) and

- Parts of the passivation layer (20) from the second main surface (3) for creating local openings (21) for contacting the silicon substrate (1) and for creating the hole areas (9) around the via holes (10) with a third Diameter (d3), which has a value between dl and d2, can be removed, in particular by etching or laser ablation.

12. The method of claim 11, further comprising removing

Sharing the passivation layer

- a further aluminum layer (22) and optionally a nickel layer is applied to the second main surface (3) for contacting the silicon substrate (1) in the hole areas (9) of the second main surface (3), in particular by sputtering or vapor deposition, and

- Parts of the further aluminum layer (22) and optional nickel layer are removed from the second main surface (3) to expose the hole areas (9) around the via holes (10) with the first diameter (dl), in particular by etching.

13. The method according to any one of the preceding claims, further comprising exposing the aluminum doping layer (6)

- a thin dielectric layer (7) is applied to the second main surface (3),

- Parts of the dielectric layer (7) from the second main surface (3) to expose hole areas (9) with the third diameter (d3) around the via holes (10) and to form solder contact surface openings (24) with a fourth diameter (d4) be removed and - a metal alloy, in particular comprising nickel, silver, copper and / or tin, on the metal contact tracks (19) of the first main surface (2) and the solder contact surface openings (24) of the second main surface (3) to reinforce the metal contact tracks (19) and / or solder contact surface openings (24) are applied galvanically and/or chemically.

14. Metal wrap-through solar cell made of a p-doped or n-doped silicon substrate (1), which has a first main surface (2) which serves as a light side in the state of use and a second main surface (2) which serves as a back side ( 3), with through-holes (10) through the silicon substrate (1) for connecting the second main surface (3) to the first main surface (2), the second main surface (3) having an aluminum doping layer (6) and the silicon Substrate (1) has a thickness of less than approximately 200 μιτι.

15. Metal wrap-through solar cell according to claim 14, wherein a passivation layer (20), which is arranged on the aluminum doping layer (6), with openings (9) and a further aluminum layer arranged on the passivation layer (20). (22) for contacting the aluminum

Doping layer (6) is provided in the openings (9).

16. Metal wrap-through solar cell according to claim 14 or 15, wherein a nickel-containing metal layer and an insulating layer (7) are arranged on the further aluminum layer (22), the insulating layer (7) being in

Hole areas (9) with a diameter d3 and in the solder contact areas (24) with a diameter d4, and these areas are covered with a solderable layer or layer sequence formed in a chemical or galvanic process.