DE102017105465A1 - Solar cell manufacturing process - Google Patents

Abstract

The invention relates to a solar cell production method for producing a solar cell, comprising the following method steps: providing a silicon substrate (1); Applying a backside passivation layer (2) to a substrate surface (12) of the silicon substrate (1) which faces away from the light in the finished solar cell for surface passivation of the substrate surface (12); Generating at least one contact opening (4) in the passivation layer (2); Applying a silicon-rich sacrificial layer (3) at least in a region around the contact opening (4); Applying an aluminum-containing metallization paste (5) on at least partial areas of the sacrificial layer (3); Performing a firing step, in which by means of heating the metallization paste (5) on the passivation layer (2), a back-side metallization (55) with a contact through the contact opening (4) is formed.

Description

The invention relates to a solar cell production process. In particular, the invention relates to a solar cell manufacturing method by means of which a solar cell with a passivation layer having one or more contact openings is produced.

Solar cells usually have a front and a back. So-called monofacial cells can only utilize incident light via their front. So-called bifacial cells can utilize incident light both on the front and on the back. This difference is structurally conditioned.

In the case of the monofacial cell, finger electrodes are printed on the front side, for example in the form of a grid structure or grid structure. The monofacial cells can pick up light across their front and utilize the light incident on the front. The back is metallised. In addition, the solar cell module usually has a backside encapsulation element that protects the backside metallization from weathering. The back of the monofacial cell therefore usually does not utilize light.

The situation is different with bifacial cells, which can receive light both on the front and on the back. Bifacial cells also have a grid structure of finger electrodes on the back as on the front. The area-related back metallization rate is usually about 4 to 20%. If the bifacial cells are incorporated in back glass modules or another transparent backsheet as a transparent backside encapsulation element, they can also generate electricity by backlighting.

The invention is based on a solar cell contact manufacturing method, comprising the following steps: providing a silicon substrate; Applying a backside passivating layer on a substrate surface of the silicon substrate facing away from light in the finished solar cell for surface passivation of the substrate surface; Generating at least one contact opening in the passivation layer; Applying an aluminum-containing metallizing paste on the passivation layer; Performing a firing step in which by means of heating the metallization paste on the passivation layer, a backside metallization is formed with a contact through the contact opening.

In the case of solar cells with contact opening (s), these are present even before the solar cell is fired in the passivation layer arranged between a substrate and a metallization paste. The contact openings are usually produced by means of laser beams in the passivation layer. The aluminum-containing metallization paste filled in the contact hole (s) is thus in contact with the substrate of semiconductor such as silicon even before firing. This results in diffusion of both the silicon into the metallization paste and the aluminum into the substrate during firing. Due to the aluminum diffusion into the substrate, a so-called back surface field (BSF) is created, which additionally has a surface passivation effect.

The metallization paste is arranged in the contact opening, since during the application of the metallizing paste, the contact opening is filled with metallizing paste. Due to the higher solubility of silicon in aluminum, silicon diffuses faster during the fire step into the aluminum in the metallizing paste than vice versa. This can lead to the formation of voids, particularly in the substrate below the backside metallization, resulting in elastic stress in the backside metallization and / or poor local back surface field (LBSF) in the solar cell thus fabricated. Darting voids also reduce the contact area between backside metallization and substrate. The performance of the solar cell produced is therefore not optimal.

It is an object of the invention to provide a solar cell manufacturing method that results in a solar cell with improved performance.

According to the invention, this object is achieved by a solar cell production method having the features of patent claim 1. Advantageous embodiments and further developments of the invention will become apparent from the following subclaims.

• - Bereitstellen eines Siliziumsubstrates;
• - Aufbringen einer rückseitigen Passivierschicht auf einer bei der fertigen Solarzelle lichtabgewandten Substratoberfläche des Siliziumsubstrates zur Oberflächenpassivierung der Substratoberfläche;
• - Erzeugen mindestens einer Kontaktöffnung in der Passivierschicht;
• - Aufbringen einer siliziumreichen Opferschicht zumindest in einem Bereich um die Kontaktöffnung;
• - Aufbringen einer aluminiumhaltigen Metallisierungspaste auf zumindest Teilbereichen der Opferschicht; und
• - Durchführen eines Feuerschrittes, bei dem mittels Erwärmen der Metallisierungspaste auf der Passivierschicht eine Rückseitenmetallisierung mit einem Kontakt durch die Kontaktöffnung hindurch entsteht.

The invention relates to a solar cell production method for producing a solar cell, comprising the following method steps:

• - Providing a silicon substrate;
• - Applying a back passivating on a in the finished solar cell light remote substrate surface of the silicon substrate for surface passivation of the substrate surface;
• - generating at least one contact opening in the passivation layer;
• - Applying a silicon-rich sacrificial layer at least in a region around the contact opening;
• - Applying an aluminum-containing metallization paste on at least partial areas of the sacrificial layer; and
• Performing a firing step in which, by heating the metallization paste on the passivation layer, a backside metallization is formed with a contact through the contact opening.

According to the invention, after applying the backside passivation layer to the provided silicon substrate and before applying the aluminum-containing metallization paste and before performing the firing step, a silicon-rich sacrificial layer is applied at least in a region around the contact opening. The silicon of this silicon-rich sacrificial layer will react during the firing step with the aluminum-containing metallization paste and reduce or avoid the out-diffusion of silicon from the silicon substrate and thus the formation of the cavities. In other words, the aluminum paste silicon will preferably absorb from the silicon-rich sacrificial layer and thereby protect the silicon substrate itself. The reaction rate of silicon out-diffusing out of the silicon substrate is at least lowered, and a LBSF contact of lesser size is formed compared to an LBSF contact made without using the silicon-rich sacrificial layer. Furthermore, an LBSF thickness and a doping level in the LBSF contact can be increased by the silicon-rich sacrificial layer.

The solar cell manufacturing method results in a solar cell having a silicon substrate on which is disposed a passivation layer having at least one contact opening on which an optional residual sacrificial layer and a backside metallization are further arranged. The backside metallization may cover the light-remote substrate surface partially or substantially over the entire surface. The solar cell manufacturing method is therefore suitable for the production of both a monofacial cell and a bifacial cell.

The silicon-rich sacrificial layer is applied at least in a region around the contact opening. The silicon-rich sacrificial layer can therefore cover the substrate surface partially or substantially completely after application. By the formulation that the silicon-rich sacrificial layer is applied at least in a region around the contact opening, it is meant that the silicon-rich sacrificial layer in a region around a already existing during application of the silicon-rich sacrificial layer contact opening and / or in an area around one after application of the silicon-rich sacrificial layer to be formed contact opening is applied. That is, the contact opening can be created before or after the deposition of the silicon-rich sacrificial layer.

The aluminum-containing metallization paste is applied to at least portions of the sacrificial layer. This means that parts of the silicon-rich sacrificial layer can be uncovered after application of the aluminum-containing metallization paste metallization paste-free or of the metallizing paste. The aluminum-containing metallizing paste can be applied, for example by means of screen printing.

The firing step, in which by heating the metallizing paste on the passivation layer, a backside metallization is formed with a contact through the contact opening, is preferably carried out in the range of 800 to 950 ° C, more preferably 900 ° C. The firing step is preferably carried out for a period of 1s-2min, preferably 2s-30s.

Suitable passivation layers are, in particular, layers of aluminum oxide, aluminum oxynitride, aluminum nitride, silicon oxide and / or silicon nitride. It is also possible to provide a plurality of passivation layers one above the other, for example a passivation layer that chemically passivates and a field effect passivating one another. The passivation layer preferably comprises a layer stack of an SiOx layer and an AlNx layer, which generally means any suitable stoichiometric composition of the elements.

In a preferred embodiment, substantially all the light-remote substrate surface is covered during the application of the metallization paste. This embodiment usually leads to the production of a monofacial cell, since an incidence of light into the photovoltaically active layer is not possible due to the full-surface backside metallization which arises from the metallization paste.

In another preferred embodiment, when the metallization paste is applied, the light-remote substrate surface is only partially covered. This means that the light-remote substrate surface remains partially metallisierungspasten-free when applying the metallizing paste. In one variant, the aluminum-containing metallizing paste is applied such that it covers at least 50%, 80%, 90% or 95% of the substrate surface. This variant preferably leads to the production of a monofacial cell. In a further variant, the aluminum-containing metallization paste is applied in such a way that it covers at most 30%, 20%, 10% or 5% of the substrate surface. This further variant leads in particular to the production of a bifacial cell.

In a preferred embodiment, the contact opening in the passivation layer is produced before the application of a sacrificial layer. Preferably, in this embodiment, the sacrificial layer is applied localized in the area around the contact opening. In areas in which the sacrificial layer is not required, for example because the aluminum-containing metallization paste is only partially applied to the light-remote substrate surface, the sacrificial layer can be removed after application. Preferably, however, the sacrificial layer is not even applied to areas in which the sacrificial layer is not needed.

In another preferred embodiment, the contact opening in the passivation layer is produced after the application of a sacrificial layer. When the contact opening is formed to extend through the sacrificial layer and the passivation layer, after the contact opening is formed, the sacrificial layer automatically surrounds the contact opening.

In a preferred embodiment, the sacrificial layer is applied in the form of a silicon-containing paste. Preferably, the silicon-containing paste contains the silicon in the form of nanoparticles. The silicon-containing paste can be applied for example by screen printing or spraying.

After the application of the silicon-containing paste and before the application of the metallizing paste, a further firing step is preferably carried out. This further firing step serves to cure or dry the silicon-containing paste. The further firing step is preferably carried out at a temperature of 500-900 ° C in a period of 1s-3min, preferably 2s-60s.

More preferably, before the application of the metallizing paste, a further firing step is carried out so that a filling of the contact opening results from the silicon-containing paste. The filling has agglomerated silicon nanoparticles. The filling may comprise amorphous or partially amorphous silicon. The filling is at least part of the silicon-rich sacrificial layer.

Preferably, the sacrificial layer is deposited on the passivation layer. For example, a layer of amorphous silicon is deposited on the passivation layer.

For the purposes of the invention, the silicon-rich sacrificial layer is a deposited silicon-containing layer or a layer which is obtained after the further firing step from the silicon-containing paste, wherein the layer of silicon in an atomic concentration of more than 80%, preferably more than 90%, particularly preferred of more than 95%, particularly advantageously more than 98%. The silicon-containing paste preferably comprises silicon nanoparticles in a weight concentration of more than 50%, preferably more than 70%, more preferably more than 80%, most preferably more than 90%, when concentrations of binders and solvents, the For a paste necessary ingredients, to be disregarded.

In a preferred embodiment, the passivation layer contains aluminum and / or nitrogen. More preferably, it contains aluminum and / or nitrogen with at least 5 atomic percent each.

In a preferred embodiment, the contact opening is produced by means of laser irradiation in the passivation layer. The contact opening in the passivation layer preferably extends through the passivation layer to the substrate surface. It is preferably a so-called local contact opening (LCO). Such a contact opening is preferably formed dot-shaped or line-shaped.

• 1a bis 1e ein erfindungsgemäßes Solarzellenherstellungsverfahren in zeitlicher Abfolge;
• 2a bis 2d ein weiteres erfindungsgemäßes Solarzellenherstellungsverfahren in zeitlicher Abfolge; und
• 3a bis 3e ein noch weiteres erfindungsgemäßes Solarzellenherstellungsverfahren in zeitlicher Abfolge.

Further properties and advantages of the invention are clarified in connection with the exemplary embodiments shown in the figures and described below by way of example. It shows schematically and not to scale:

• 1a to 1e a solar cell production process according to the invention in chronological order;
• 2a to 2d another solar cell production process according to the invention in chronological order; and
• 3a to 3e a still further inventive solar cell production process in chronological order.

1a to 1e show a solar cell manufacturing method according to the invention in chronological order, wherein in each case a cross-sectional view of a silicon substrate is shown after a manufacturing step. In 1a is a provided silicon substrate 1 shown on the substrate surface facing away from light in the finished solar cell 12 a backside passivation layer 2 for surface passivation of the substrate surface 12 has been applied. Subsequently, a silicon-rich sacrificial layer 3 on the passivation layer 2 applied, wherein substantially an entire light-remote surface of the passivation 2 is covered as in 1b is shown. Then, a contact opening in the passivation layer 2 generated localized by means of a laser, so that the silicon-containing sacrificial layer 3 is arranged in the area around the contact opening 4, as in 1c is shown. The contact opening 4 extends through the silicon-rich sacrificial layer 3 and the passivation layer 2 to the silicon substrate 1 ,

Subsequently, an aluminum-containing metallizing paste 5 applied to the sacrificial layer 3, as in 1d is shown. Then, a firing step is carried out by heating the metallizing paste 5 on the passivation layer 2 a backside metallization 55 is formed with a contact through the contact opening (not shown), as in 1e is shown. This can be an optional residual sacrificial layer 31 between the backside metallization 55 and the passivation layer 2 arise. In addition, arises in the silicon substrate 1 adjacent to the backside metallization 55 in the contact opening (not shown) a back surface field 51 , 1e shows the produced solar cell which is a monofacial cell.

2a to 2d show a further inventive solar cell production process in chronological order, wherein in each case a cross-sectional view of a silicon substrate is shown after a manufacturing step. After providing a silicon substrate 1 a passivation layer 2 is applied to a substrate surface 12 of the silicon substrate that faces away from the light in the finished solar cell 1 for surface passivation of the substrate surface 12 applied and a contact opening 4 produced in the passivation layer, extending through the passivation layer 2 through to the silicon substrate 1 extends. This is in 2a shown. Subsequently, a silicon-containing sacrificial layer 3 in an area around the contact opening 4 applied, wherein it is applied so that it the contact opening 4 covered, but parts of the passivation remain uncovered, as in 2 B is shown.

Then an aluminum-containing metallizing paste 5 on the sacrificial layer 3 and the passivation layer 2 applied, so that the light-remote side of the substrate 1 is substantially completely covered, as in 2c is shown. Subsequently, a firing step is carried out, in which by heating the metallizing paste 5 on the passivation layer 2 a backside metallization 55 with contact through the contact opening 4 is formed through and in the silicon substrate 1 adjacent the backside metallization 55 in the contact opening (not shown) is a back surface field 5 arises, as in 2d is shown. 2d shows the produced solar cell which is a monofacial cell.

3a to 3e show a still further inventive solar cell manufacturing process in chronological order, wherein in each case a cross-sectional view of a silicon substrate is shown after a manufacturing step. After providing a silicon substrate 1 a passivation layer 2 is applied to a substrate surface 12 of the silicon substrate that faces away from the light in the finished solar cell 1 for surface passivation of the substrate surface 12 applied and a contact opening 4 produced in the passivation layer, extending through the passivation layer 2 extends to the silicon substrate 1. This is in 3a shown.

Subsequently, a silicon-containing sacrificial layer 3 in the form of a silicon-containing paste in an area around the contact opening 4 applied, wherein it is applied so that it the contact opening 4 covered, but parts of the passivation layer 2 uncovered, as in 3b is shown. Subsequently, a fire step is carried out, so that from the silicon-containing paste a filling 34 the contact opening (not shown) is formed as in 3c is shown. Then, an aluminum-containing metallizing paste 5 on the filling 34 and the passivation layer 2 applied, as in 3d is shown. Subsequently, a firing step is performed, in which by means of heating the metallizing paste 5 on the passivation layer 2 a backside metallization 55 with a contact through the contact opening (not shown) is formed, wherein in the silicon substrate 1 adjacent to the backside metallization 55 in the contact hole (not shown) a back surface field 5entseht, as in 3e is shown. 3e shows the produced solar cell which is a monofacial cell.

In all of the manufacturing processes shown in the figures, the aluminum-containing metallizing paste becomes 5 all over the sacrificial layer 3 or Passivierschicht 2, ie on the entire substrate surface 12 applied, resulting in the production of a monofacial cell. Alternatively, the solar cell production methods shown in the figures can also be modified such that the application of the aluminum-containing metallization paste 5 is carried out such that only a part of the sacrificial layer 3 is covered and the passivation layer 2 from the aluminum-containing metallizing paste 5 is at least partially uncovered, so that the solar cell manufacturing process lead to the production of a bifacial cell.

LIST OF REFERENCE NUMBERS

1 silicon substrate 2 Passivation layer 3 sacrificial layer 30 Rest sacrificial layer 34 filling 4 contact opening 5 metallizing 51 Back-surface field 55 backside metallization

Claims (10)

Solar cell production process for producing a solar cell, comprising the following process steps: - Providing a silicon substrate (1); - Applying a back passivating layer (2) on a in the finished solar cell light remote substrate surface (12) of the silicon substrate (1) for surface passivation of the substrate surface (12); - generating at least one contact opening (4) in the passivation layer (2); - Applying a silicon-rich sacrificial layer (3) at least in a region around the contact opening (4); - Applying an aluminum-containing metallizing paste (5) on at least partial areas of the sacrificial layer (3); and - Performing a firing step, in which by means of heating the metallization paste (5) on the passivation layer (2), a back-side metallization (55) with a contact through the contact opening (4) is formed. Production method according to Claim 1 , characterized in that during the application of the metallization paste (5) substantially the entire light-remote substrate surface (12) is covered. Production method according to Claim 1 or 2 , characterized in that the contact opening (4) is produced in the passivation layer (2) before the application of a sacrificial layer (3). Production method according to Claim 1 or 2 , characterized in that the contact opening (4) is produced in the passivation layer (2) after the application of a sacrificial layer (3). Production method according to Claim 3 , characterized in that the sacrificial layer (3) is applied localized in the area around the contact opening (4). Manufacturing method according to one of the preceding claims, characterized in that the sacrificial layer (3) is applied in the form of a silicon-containing paste. Production method according to Claim 6 , characterized in that prior to the application of the metallizing paste (5), a further firing step is carried out, so that from the silicon-containing paste, a filling (34) of the contact opening (4) is formed. Manufacturing method according to one of Claims 1 to 5 , characterized in that the sacrificial layer (3) is deposited on the passivation layer (2). Production method according to one of the preceding claims, characterized in that the passivation layer (2) contains aluminum and / or nitrogen, preferably each with at least 5 atomic percent. Manufacturing method according to one of the preceding claims, characterized in that the contact opening (4) is produced by means of laser irradiation in the passivation layer (2).

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