SWIATKOWSKI, Carsten (Nassauische Straße 24, Berlin, 10717, DE)
SCHERFF, Maximilian (Heroldstraße 28, Dortmund, 44145, DE)
MÜLLER, Jörg (Pestalozzistraße 15 a, Sandersdorf, 06792, DE)
KUX, Andreas (Maierfeldweg 4, Haar, 85540, DE)
HLUSIAK, Markus (Oppenheimstraße 4 b, Wolfen, 06766, DE)
SWIATKOWSKI, Carsten (Nassauische Straße 24, Berlin, 10717, DE)
SCHERFF, Maximilian (Heroldstraße 28, Dortmund, 44145, DE)
MÜLLER, Jörg (Pestalozzistraße 15 a, Sandersdorf, 06792, DE)
KUX, Andreas (Maierfeldweg 4, Haar, 85540, DE)
| Claims: 1 . Method for marking a solar cell, comprising the following steps: - Providing a solar cell substrate (1 ); - Selecting an identification pattern for identifying the solar cell substrate (1 ) during process steps of a manufacturing process for the solar cell and / or for tracing back the solar cell substrate (1 ) after assembly of the solar cell in a solar cell module; - Forming an etch resist layer (3) on a surface (2) of the solar cell substrate (1 ); - Etching the surface (2) of the solar cell substrate (1 ) with an etchant, whereby the etch resist layer (3) is formed in such a way that a pattern region (4) of the surface (2) in the shape of the identification pattern is protected from the etchant. 2. Method according to claim 1 , characterized by that the etching step comprises a damage etching and / or a texture etching step. 3. Method according to one of the previous claims, characterized by that the etch resist layer (3) is removed from the surface (2) of the solar cell substrate (1 ) after the etching step. 4. Method according to claim 1 or 2, characterized by that the etch resist layer (3) is substantially or completely removed from the surface (2) of the solar cell substrate (1 ) during the etching step. 5. Method according to claim 3 or 4, characterized by performing a damage etching step before and a texture etching step after removal of the etch resist layer (3). 6. Method according to claim 1 or 2, characterized by that a part or all of the etch resist layer (3) remains on the surface (2) of the solar cell substrate (1 ) during the following solar cell production process and / or in the finished solar cell and /or the solar cell module. 7. Method according to one of the previous claims, characterized by that the reflectivity of the surface (2) of the solar cell substrate (1 ) is reduced by the etching step. 8. Method according to one of the previous claims, characterized by that the charge carrier recombination rate at the surface (2) of the solar cell substrate (1 ) is reduced by the etching step. 9. Method according to one of the previous claims, characterized by that the etchant comprises an etching liquid and / or an etching plasma. 10. Method according to one of the previous claims, characterized by that the pattern region (4) in the shape of the identification pattern is positioned in an active portion (21 ) of the surface (2) of the solar cell produced from the solar cell substrate (1 ). 1 1 . Method according to one of the claims 1 to 9, characterized by that the region in the shape of the identification pattern is positioned outside an active portion (21 ) of the surface (2) of the solar cell produced from the solar cell substrate (1 ), in a peripheral portion (22) of the solar cell substrate (1 ). 12. Solar cell comprising a solar cell substrate (1 ) with a damage etched surface (2) and / or a textured surface (2), whereby the texture of the textured surface (2) is produced by texture etching using an etchant, the damage etched and / or textured surface (2) comprising a region with lower recombination rate and / or a texture free region in the shape of an identification pattern for identifying the solar cell substrate (1 ). |
Method for marking a solar cell, and solar cell Description:
The invention relates to a method for marking a solar cell as well as to a solar cell. Such a marking may be necessary in order to be able to track a solar cell during the manufacturing process and afterwards.
Regularly, such a marking consist of a print or etch mark comprising a numerical or alphanumerical code being printed or etched onto a surface of a substrate of the solar cell very early in the manufacturing process. Other patterns, e.g. a bar code, may also be useful, as long as they are suitable to uniquely identify the substrate. Such a marking pattern needs to be robust enough to survive the many processing steps that are being performed on the substrate for producing the solar cell.
Patterns printed onto the surface of the substrate are often in danger of being wiped off the surface during etching or firing processes or covered during deposition processes necessary for the solar cell manufacture. On the other hand, patterns etched or scribed onto the substrate surface, e.g. by laser scribing, have the disadvantage, that obtaining a dominant and easily detectable pattern requires deep trenches to be engraved into the substrate surface. This process is accompanied by the danger of thinning out the substrate locally to an extent of producing potential mechanical breaking spots and / or electrical shunt spots. In extreme cases, the etching or scribing may accidentally reach all the way through the substrate.
It is an object of the present invention to provide for a method for marking solar cell, and for a solar cell, allowing efficient tracking of the solar cell during the manufacturing process and beyond, while minimizing the risk of damage. The object is achieved in this invention by providing a method for marking a solar cell with the features of claim 1 , and a solar cell with the features of claim 10. Advantageous embodiments of the invention are subject of the sub- claims.
The invention is based on the concept of marking a solar cell by protecting the marking region with a detectable pattern, while exposing the rest of the surface to a surface altering procedure. Thus, instead of altering the marking region in the shape of an identification mark, there remains a patterned region in the shape of the identification pattern unaltered on the substrate. The surface altering procedure is an etch procedure which has to be performed on a solar cell substrate in the course of the manufacturing process for the solar cell. Therefore, no additional surface altering is performed in order to create the identification pattern.
The detection of the identification pattern may be performed by optical or electro-optical means. In particular, minority carrier lifetime measurements along the substrate surface may reveal the identification pattern and / or allow finding the pattern region automatically. Advantageously, optical imaging processes may be utilized, which allow reading out the entire pattern at once, such as for example lifetime mapping or photoluminescence or electroluminescence imaging. This may include the scanning of bar codes. This method of reading out the identification pattern may be performed any time during the further manufacturing process of the solar cell.
The etching process in preferred embodiments comprises a damage etching and / or a texture etching step. A texture etch process is a process, whereby a front surface of the solar cell is patterned to raise the light absorption rate of incident light and thus improve the efficiency of the solar cell. On the other hand a damage etching process may be performed to remove damage on the substrate surface stemming from the manufacture of the substrate, such as saw damage. In the latter case, the patterned region may be detected due to its higher amount of surface damage, such as saw damage, which leaves the surface of the substrate jagged or rough. In this region the carrier
recombination rate is high compared to the damage etched region and the lifetime will be smaller than in damage etched areas especially if the surfaces will be passivated in one of the following process steps. Alternatively, the etching process may be performed in order to remove a previously deposited or grown layer from the substrate. It may be either a dry or a wet etching process, possibly supported by a plasma discharge. Preferred embodiments may include, but are not limited to, the following orders of process steps performed on the solar cell substrate:
Forming the etch resist layer, then performing a damage etch, and then performing a texture etch;
Performing a damage etch, then forming the etch resist layer, and then performing a texture etch;
Forming the etch resist layer, then performing a damage etch, without performing a texture etch at all; or
Forming the etch resist layer, then performing a texture etch, without performing a damage etch at all.
In any embodiment, forming the etch resist layer may be either performed by covering the entire surface area by an etch resist material and patterning the resist layer afterwards, for example by use of known lithographical techniques Alternatively, the etch resist layer may be deposited onto the surface of the substrate in patterned form, for example by ink jet printing or screen printing dispensing or the like.
The identification pattern may represent an alphanumeric code or a code in a number system, for example a binary code. After performing the etching step, a non-etched region is left on the surface, which has the shape of the identification pattern. This region may still be covered by the etch resist layer, in which case the remaining etch resist layer may be removed after the etching step or left on the patterned region in order to increase the readability of the pattern. The remaining etch resist layer may be left on the solar cell substrate in particular if it is made of a material that may withstand the following process steps. Such materials include for example substances that form silicon dioxide, such as spin-on Si02. However, advantageously, the etch resist layer is substantially or completely removed from the surface of the solar cell substrate during the etching step. In particular, the etchant used in the etching step may also attack the etch resist, although at an etch rate which is just low enough to prevent any further etching of the substrate underneath the etch resist layer.
In a preferred embodiment, a damage etching step is performed before and a texture etching step is performed after removal of the etch resist layer. In this case, the pattern region is protected by the etch resist layer while performing the damage etching step, thus leaving any manufacturing damage on the pattern region. Afterwards, or during the damage etching step, the etch resist layer is removed and the pattern region is exposed to the texture etching. During the texturing the formerly (with the etch resist) protected area is textured also, but some surface damage will remain in the surface. Therefore, the identification pattern may in this case be detected as a region with higher density of manufacturing damage and can be detected by means of lifetime mappings.
In an advantageous embodiment, the reflectivity of the surface of the solar cell substrate is reduced by the etching step, in particular by the texture etching step. Therefore, because the pattern region is protected from the etch by the etch resist layer, it will have a higher reflectivity than the rest of the substrate surface. This might aid to detect and read-out the identification pattern optically. Additionally, or alternatively, the charge carrier
recombination rate at the surface of the solar cell substrate may be reduced by the etching step, in particular by the damage etching step.
In particularly advantageous embodiments, the damage etching and the texture etching of the surface is performed during a single etching step, namely by extending the texture etching step by a certain time and / or by adjusting other parameters of the texture etchant, such that the texture etching step also removes most of or all the surface damage and reduces the recombination rate on the surface.
In preferred embodiments, the etchant used for the etching step comprises an etching liquid and / or an etching plasma. In particular, an anisotropic etchant may be used for this purpose.
In a preferred embodiment, the pattern region in the shape of the
identification pattern is positioned in an active portion of the surface of the solar cell produced from the solar cell substrate. The active portion of the substrate is the surface region that is used to absorb the incident light and transform it to electrical current. When using traditional marking techniques, such as a label or laser scribed patterns, the identification mark may interfere with the photovoltaic activity, if placed in the active region. If, however, the pattern region differs only by its surface quality from the rest of the active region, there might only be a minimal loss in photovoltaic efficiency, while still allowing the detection of the identification pattern.
Alternatively, the region in the shape of the identification pattern may be positioned outside an active portion of the surface of the solar cell produced from the solar cell substrate, in a peripheral portion of the solar cell substrate. In particular, the identification pattern may be positioned along the edge of the substrate, which may be a semiconductor wafer.
An example of an embodiment of the invention will be explained in more detail in the following description with reference to the accompanying schematic drawings, wherein Fig. 1 to 5 show a schematic cross section view of a solar cell substrate in different stages during a marking method according to a preferred embodiment. During the marking process, first a solar cell substrate 1 with a surface 2 is provided, as shown in Fig. 1. Next, as illustrated in Fig. 2, the surface 2 of the substrate 1 is covered with an etch resist layer 3. In a further step, as shown in Fig. 3, the etch resist layer 3 is patterned such that a portion of the etch resist layer 3 remains on a pattern region 4 of the substrate 1. The remaining etch resist layer 3 has the shape of an identification pattern representing an identification code for identifying the substrate during and after a
manufacturing process. Patterning of the etch resist layer 3 may be performed by known lithographical techniques, by ink jet or screen printing dispensing or the like.
In a next step, the surface 2 of the substrate 1 is etched, resulting in a surface structure schematically depicted in Fig. 4. It shows the region of the surface 2 not protected by the etch resist layer 3 to be textured due to a texture etch. However, in other embodiment, the etching step may include a defect etching process.
In the case shown in Fig. 4, the pattern region 4 is positioned in a peripheral portion 22 of the solar cell substrate 1 , while an active portion 21 is kept free of the etch resist layer 3. Alternatively, the identification pattern may be formed at least partly on the active portion 21 of the substrate 1.
Finally, as depicted in Fig. 5, the remaining portion of the etch resist layer 3 is removed from the pattern region 4 of the surface 2. This may allow also the pattern region 4 to be utilized in the further manufacturing process of the solar cell, in particular if the pattern region 4 is positioned in the active portion 21 of the surface. In alternative embodiment, the remaining etch resist layer 3 may be left on the surface 2 of the substrate 1 in order to improve the ability to detect the identification pattern or to simply save an additional etching step. In yet other embodiments, the etching step is designed such that the remaining etch resist layer 3 is removed from the pattern region 4 during the etching step, without attacking the pattern region 4. Reference Numerals:
1 solar cell substrate
2 surface of the solar cell substrate
21 active portion
22 peripheral portion
3 etch resist layer
4 pattern region
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