FIELD

[0001 ] Embodiments of the present disclosure relate to a method and an apparatus for use in substrate processing. Embodiments of the present disclosure particularly relate to a method and an apparatus that allows a substrate processing to run continuously. Even more speci fically, embodiments of the present disclosure allow for the exchange of a substrate loading stack arrangement without the interruption of the substrate processing. The embodiments of the present disclosure particularly relate to processing solar cell substrates.

BACKGROUND

[0002 ] Solar cells are photovoltaic (PV) devices that convert sunlight directly into electrical power. Within this field, it is known to produce solar ceils on a substrate such, as a crystalline silicon base using disposition techniques, such, as screen printing, achieving a structure of electrically conductive line patterns on one or more surfaces of the solar cells. A system for production of solar cel ls can be arranged along a processing line for processing the substrates. Substrates that arc intended to be processed can be prov ided in substrate loading stack arrangements. The substrates are discharged from the substrate loading stack arrangements in a piece-by-piece manner and thereby typically loaded onto the processing line for further processing.

[0003] While the discharging of a charged substrate loading stack arrangement can be done in a quasi-continuous process, the exchange of an emptied substrate loading stack arrangement causes an interruption of the substrate loading to the further processing. The methods for a particularly quick replacement of the emptied loading stack arrangement with a new, fully filled loading stack arrangement that have been proposed so far have proven to be unsatisfactory. [0004 ] I view of the above, a new method and apparatus for continuously loading substrates to a manufacturing process would be beneficial that overcome at least some of the problems in the art.

SUMMARY

[0005] In light of the above, a method for processing substrates according to the independent method claim, and an apparatus for processing substrates according to the independent apparatus claim are provided. Further details, aspects, optional features and advantages of the present disclosure are evident from the dependent claims, the detailled description and the figures.

[0006] According to an aspect of the present disclosure, a method for processing substrates is provided. The method includes providing a substrate loading stack arrangement including a multitude of substrates, unloading the multitude of substrates from the substrate loading stack arrangement at a first rate, and fill ing a substrate buffer with substrates from the substrate loading stack arrangement with a first part of the multitude of substrates at a second rate, wherein the second rate is smaller than the first rate.

[0007] According to a further aspect of the present disclosure, an apparatus for processing substrates is provided. The apparatus includes a reception for arranging a substrate loading stack arrangement, at least one transport device for transporting a multitude of substrates from the substrate loading stack arrangement to a substrate buffer, and a controller configured for controll ing the substrate loading stack arrangement to unload the multitude of substrates from the substrate loading stack arrangement at a first rate and for controlling the substrate buffer to load a first part of the multitude of substrates into the substrate buffer at a second rate, wherein the second rate is smaller than the first rate.

[0008] According to another aspect of the present disclosure, a method for processing substrates is provided. The method includes providing a substrate loading stack arrangement including a multitude of substrates, unloading the multitude of substrates from the substrate loading stack arrangement at a first rate, and filling a substrate buffer with substrates from the substrate loading stack arrangement with a first part of the multitude of substrates at a second rate, wherein the second rate is smaller than the first rate. Moreover, according to the method, the second rate is half ( i.e., 1/2) of the first rate. Alternatively or additionally, the fi st part of the multitude of substrates is hal f of the multitude of substrates. The first part of the substrates from the substrate buffer are unloaded at the first rate once the substrate loading stack arrangement is empty.

[0009] According to another aspect of the present disclosure, an apparatus for processing substrates is provided. The apparatus includes a reception for arranging a substrate loading stack arrangement, at least one transport device for transporting a multitude of substrates from the substrate loading stack arrangement to a substrate buffer, and a controller configured for controll ing the substrate loading stack arrangement to unload the multitude of substrates from the substrate loading stack arrangement at a first rate, and for controlling the substrate buffer to load a first part of the multitude of substrates into the substrate buffer at a second rate, wherein the second rate is smaller than the first rate. Moreover, according to the method, the second rate is half (i.e., 1/2) of the first rate. Alternatively or additionally, the first part of the multitude of substrates is half of the multitude of substrates. The controller is con figured to unload the fi st part of substrates from the substrate buffer at the first rate once the substrate loading stack arrangement is empty.

[001 0] All method actions as described herein can generally be controlled by the controller as described herein. The controller as described herein may be configured to execute the method actions as described herein.

[001 1 ] Embodiments are also directed at apparatuses for carrying out the disclosed method and include apparatus parts for performing each described method aspect. These method aspects may be performed by way of hardware components, a computer programmed by appropriate software, by any combination of the two or in any other manner. Furthermore, embodiments according to the disclosure are also directed at methods for operating the described apparatus. The methods for operating the described apparatus include method aspects for carrying out every function of the apparatus.

BRIEF DESCRIPTION OF THE DRAWINGS [0012] So that the manner in which the above recited features of the present disclosure can be understood in detail, a more particular description of the disclosure, briefly summarized above, may be had by reference to embodiments. The accompanying drawings relate to embodiments of the disclosure and are described in the following: FT (Is. 1 to 6 show schematic illustrations of the apparatus for processing substrates according to embodiments described herein;

FIG. 7 shows a schematic illustration of an exemplary transport device according to embodiments described herein according to which the transport device is a printing nest; and

FIG. 8 shows a schematic illustration of a method for processing substrates according to embodiments described herein.

DETAILED DESCRIPTION OF EMBODIMENTS

[0013] Reference will now be made in detail to the various embodiments of the disclosure, one or more examples of which are illustrated in the figures. Within the fol lowing description of the drawings, the same reference numbers refer to same components. Generally, only the differences with respect to individual embodiments are described. Each example is provided by way of explanation of the disclosure and is not meant as a limitation of the disclosure. Further, features illustrated or described as part of one embodiment can be used on or in conjunction with other embodiments to yield yet a further embodiment. It is intended that the description includes such modifications and variations. [0014] Fig. 1 exemplariiy shows an apparatus for processing substrates. The apparatus for processing substrates may also be referred to as "processing line" herein. Generally, and not limited to the embodiment of Fig. 1 , the apparatus may include one or more transport devices 3, 4, and 5, such as conveyors, or more specifically, conveyor belts. The apparatus typically includes at least one processing station. One processing station is schematically shown in the embodiments of the figures and referred to by the numeral 6. Not l imited to any embodiment, the apparatus as described herein may include at least two, at least three, or even more processing stations. [0015] The one or more processing stations as described herein may be selected from the group including: A substrate unloading station, a printing station, an alignment station, a buffer station, an inspection station, a heating station, a scribing station, a cutting station, a cleav ing station, a gluing station, a binning station, and any combinations thereof.

[00 1 6 ] In some implementations, the apparatus is configured for substrate processing, such as screen printing, inkjet printing, laser processing (e.g., laser scribing), flexo printing, gravu e printing, tampography, laser transfer printing, and the l ike. In particular, the apparatus can be configured for substrate processing using techniques capable of transferring a pattern into or onto the substrate. For example, the apparatus can be configu ed for printing, such as screen printing. In some implementations, the processing station may include one or more printing heads and one or more screen devices for screen printing of patterns such as fingers and/or busbars on the substrate for the production of a solar cell. In some embodiments, the screen device defines a pattern or features corresponding to a structure to be printed on the substrate, wherein the pattern or features may include at least one of holes, slots, incisions, scribed recesses or other apertures. [00 1 7 ] The present embodiments arc specifically useful for use in a manufacturing process for shingled solar cells. In implementations, the substrate loading stack arrangement is loaded w ith substantially quadratic substrates. The substantially quadratic substrates may hav e cuts at their four corners as is usual for example for monocrystalline solar cells. Later processing stations may include one or more processing stations to scribe and/or cleave the substrate, and one or more processing stations to distribute the substrate into a number of substrate strings, such as 4 to 6 substrate strings. Those substrate strings are then typical ly glued together to form shingled solar cell substrates.

[0018] The substrate loading stack arrangement and the substrate buffer are typically provided with so-called substrate trays that are abbrev iated to "trays" herein . Each of the trays is adapted to receive one substrate. The number of trays of the substrate loading stack arrangement may be in the range of more than 50, or even more than 1 00. The number of trays in the substrate buffer typically corresponds to half of the number of trays in the substrate loading stack arrangement. For instance, the substrate buffer may have more than 25 trays, or the substrate buffer may even have more than 50 trays. [0019] The apparatus as described herein may include a substrate unloading station for unloading the substrates from the processing line. The substrate unloading station is ty ical ly arranged after the substrates have been partly or fully processed. Substrate unloading can be done into a substrate unloading stack arrangement. In some implementations, the substrate unloading stack arrangement is identical to a substrate loading stack arrangement as described herein. The substrate unloading stack arrangement can be positioned after the substrate has undergone one or more processing action in the one or more processing stations.

[0020] At an unloading site of the apparatus for processing substrates (i.e. the site of the apparatus where some or all of the processing has already taken place) as described herein, a further substrate buffer may be prov ided. The substrate buffer at the unloading site is typically operated such that it is filled with substrates when a substrate unloading stack arrangement is being replaced with a new substrate unloading stack arrangement. Once the new substrate unloading stack arrangement is installed, substrates from the buffer a e unloaded and led to the new substrate unloading stack arrangement. At the same time, processed substrates may be fed directly from the processing line to the new substrate unloading stack arrangement.

[002 1 ] Turning back to the exemplary illustration of Fig. 1 , the embodiment shows the processing line including the conveyors 3, 4, and 5, a substrate buffer 2, and a processing station 6. Further, a reception for the substrate loading stack arrangement is schematically shown. The reception is denoted by reference number 1 1. Generally, and not limited to any embodiment, the reception shall be representative for the apparatus ^' ability to be operated in connection with a substrate loading stack arrangement. Hence, a reception may be understood as the position where the substrate loading stack arrangement is supposed to be placed for operating the apparatus according to the present embodiments. A reception may include one or more guides for receiv ing the substsratc loading stack arrangement. In other embodiments, the reception may simply be the ground on which the substrate loading stack arrangement can be placed.

[0022] In the follow ing figures, where the substrate loading stack arrangement is depicted as being received by the reception, the reception 1 1 is no longer shown but concealed by the substrate loading stack arrangement. The substrate buffer is exemplarily depicted as empty in Fig. 1 , i.e., the trays 8 of the substrate buffer in Fig. 1 do not accommodate a substrate.

[0023] As schematically shown in Fig. 2, a substrate loading stack arrangement 1 has been mounted to the beginning of the processing line. As shown in Fig. 2, the substrate loading stack arrangement 1 is filled with substrates 10. For illustrative purposes, the lower-most three substrates are referred to by numerals 1 0- 1 , 10-2, and 10-3 in the following. In the embodiments described herein, the trays of the substrate loading stack arrangement are labelled with reference number 9.

[0024] Generally, and not limited to the embodiment of Fig. 2, the substrate loading stack arrangement may be prov ided and mounted to the reception 1 1 automatically, e.g. by a robot. Alternatively, it may be provided and mounted to the reception 1 1 manually. The apparatus and/or correspondingly the substrate loading stack arrangement may be provided with one or more quick relea.se fasteners. This is beneficial in that it allows for a quick exchange of an empty substrate loading stack arrangement with a fully loaded substrate loading stack arrangement.

[0025] As used herein, the term "empty substrate loading stack arrangement", "empty substrate buffer", or "empty unloading stack arrangement" particularly relate to a situation where no or only few substrates are left in the substrate loading stack arrangement, substrate buffer, or substrate unloading stack arrangement, respectiv ely. For instance, due to processing reasons, it may be beneficial for the process that 10% at ma imum, or ev en up to 15% of the substrate trays are still filled with a substrate when the substrate loading stack arrangement is replaced, or the substrate buffer is filled again with substrates. In the context of the present disclosure, filling rates of up to 15% or up to 10% shall still be understood as empty. [0026] Similarly, as used herein, the term "full substrate loading stack arrangement ^"* , "full substrate buffer", "full unloading stack arrangement ^" ', or similar terms such as "fully loaded substrate buffer" particularly relate to a situation where all the substrate trays, or almost all of the substrate trays are filled with substrates. For instance, due to processing reasons, it may be beneficial for the process that, for instance, only 90%, or only 80% of the substrate trays are filled in the substrate loading stack arrangement or substrate buffer. In the context of the present disclosure, those filling rates shall still be understood as "full" or "fully loaded".

[0027] Fig. 3 schematically and exemplarily shows a situation where the processing of substrates has already started. After unloading the first substrate 10-1, the substrate loading stack arrangement is controlled to be lowered by one tray so as to allow the second substrate 10-2 to be loaded on the first transport device. This is schematically illustrated with the arrow shown adjacent to the substrate loading stack arrangement 1 in Fig. 3. The multitude of substrates 10 are unloaded from the substrate loading stack arrangement 1 on the first transport device 3. The first substrate 10-1 unloaded from the substrate loading stack arrangement 1 is depicted as being advanced to the second transport device 4. In the illustrations of Figs. 1 to 6 described herein, the movement direction of the substrates is from left to the right. The first substrate 10- 1 will therefore be subject to a processing action in the processing station 6. [0028] As exemplarily shown in Fig. 3, the second substrate 10-2 unloaded from the substrate loading stack arrangement and transported by the first transport device 3 has been picked up by the substrate buffer 2. Thereby, in possible implementations of a substrate buffer, the substrate buffer raises by one tray after picking up a substrate so as to allow for a further substrate to be picked up. This is exemplarily indicated by the schematic arrow adjacent to the substrate buffer 2. As can be seen in the illustrated schematic drawings, according to embodiments described herein, the substrate loading stack arrangement and the substrate buffer are both arranged to act on the same transport device, such as the first transport device in the drawings. In other words, the substrate buffer is positioned so as to load substrates from, and unload substrates to, the same transport device to which the substrate loading stack arrangement is positioned to unload substrates. [0029 ] According to implementations described herein that can be combined with other embodiments, further to the substrate buffer's functionality to store substrates, the substrate buffer is configured to allow substrates to pass through. According to embodiments, every second substrate is picked up by the substrate buffer, whereas the other substrates are allowed to pass through, or pass by, the substrate buffer so as to be further processed on the processing line without any intermediate storage. Consequently, in embodiments, the first rate at which the substrate loading stack arrangement is unloaded is twice (i.e., two times) the second rate at which the substrate buffer is loaded. Further, the first rate for unloading the substrates from the substrate loading stack arrangement is typically larger than the processing speed of the apparatus as described herein.

[0030] The term "processing speed" refers to the smallest maximum speed of all processing stations provided in the apparatus for processing substrates. For instance, if one processing stat ion is a first printing device that can be operated at a maximum speed of one wafer per 0.8 seconds, whereas the further processing stations can be operated with a maximum speed of one wafer per 0.7 seconds, the processing speed of the apparatus for processing is one wafer per 0.8 seconds.

[0031] As used herein, the term "rate ^" in relation to the handl ing of substrates, in particular in relation to the loading or unloading of substrates, is expressed as the number of substrates per time unit. For instance, if unloading the substrates from the substrate loading stack arrangement is performed at a higher rate than the loading of the substrate buffer, this can be understood in that the number of substrates that are taken out of the substrate loading stack arrangement per time unit (e.g. per seconds) is larger than the number of substrates that are used for fill ing the substrate buffer per time (e.g. per seconds). [ 0032] As still shown in Fig. 3, the third substrate 1 0-3 is being unloaded from the substrate loading stack arrangement. As in the embodiment shown, only every second substrate is buffered in the substrate buffer 2, the substrate 10-3 will be controlled to pass through the substrate buffer 2 to directly reach the processing station 6.

[0033] In the same way, according to the embodiment shown, the fourth substrate unloaded from the substrate loading stack arrangement will be stored in the substrate buffer 2, whereas the fifth substrate will pass through the substrate buffer to be processed, etc.

[0034] In typical embodiments, the speed of the first transport device is constant, for instance, no more than 400 mm/s. The reason for operating below a threshold speed value such as 400 mm/s is that this speed still allows for an acceptable amount of friction between transport device and substrates at the moment of gripping, or releasing, the substrates; in typical embodiments, the speed of the processing is higher, though.

[00 51 The speed of the second transport device may vary in order to accelerate the substrates. The second transport device may be understood as a "speed change transport device". For instance, the second transport device may be operated such that its speed alternatingly changes between a low transport speed, which could be the same speed as the speed of the first transport device, and a high transport speed, which could be the same speed as the speed for processing the substrates (e.g., corresponding to the smallest maximum speed of the subsequent processing stations). For instance, the low transport speed of the second transport device may be between 300 and 400 mm/s, whereas the high transport speed of the second transport device may be between 600 and 800 mm/s.

[0036] The speed of the third transport device may be held constant, such as at a speed corresponding to the processing speed (e.g., between 600 and 800 mm/s). Notably, the language "high transport speed" and "low transport speed", respectively, is used for the sake of clarity and plasticity herein. Likewise, the terms "second transport speed" and "fourth transport speed", respectively, could be used instead.

[0037] Coming back to the figures, the illustrated operation of a combined processing and buffering continues until the substrate loading stack arrangement is emptied. Such a situation is exemplarily shown in Fig. 4. At that point in time, the substrate loading stack arrangement 1 is typically replaced by a fully filled substrate loading stack arrangement. In order to continue with the processing of substrates during the exchange of the substrate loading stack arrangement, the substrate buffer 2 is emptied and provides further substrates to be processed. This is exemplarily indicated by the schematic arrow next to the substrate buffer 2 in Fig. 4 illustrating that the moving direction of the substrate buffer 2 changes, once fully filled with substrates, in order to unload substrates again. The substrates may be unloaded from the substrate buffer at the second rate. Meanwhile, while the processing of substrates continues, a robot or an operator has sufficient time to replace the empty substrate loading stack arrangement with a full substrate loading stack arrangement.

[0038] In traditional apparatues for processing substrates, the time to exchange the empty substrate loading stack arrangement with a fully loaded substrate loading stack arrangement is highly critical. Embodiments of the present disclosure, however, allow for the continuation of the substrate processing with sufficient time for an exchange of the substrate loading stack arrangement.

[0039 ] Fig. 5 is a schematic view of a situation where the substrate buffer 2 is being emptied while the substrate loading stack arrangement is being exchanged. As can be seen in this illustration, the processing is not interrupted but the substrates 1 0 are unloaded from the substrate buffer 2 to undergo a processing in the next processing station 6 while the reception 1 1 is presently without any substrate loading stack arrangement.

[0040] As described herein, the embodiments may include a controller that may particularly be con figured to control one or more of the follow ing devices: The substrate loading stack arrangement, the substrate buffer, the one or more transport devices, and the one or more processing stations. The controller may be connected to these devices via a connecting line or via a wireless connection.

[0041 1 Fig. 6 is a schematic view similar to Fig. 3, however. Fig. 6 also schematically illustrating a controller 20 that is operatively connected to the substrate loading stack arrangement 1 , the substrate buffer 2, the one or more transport devices 3, 4, and 5, and the processing station 6 by connection lines. Ev idently, as in many embodiments of the present disclosure, there is more than one processing station (not show n ), also the further processing stations may be connected to the controller. Notably. Fig. 6 is not an embodiment alternative to the further embodiments described herein. Rather, the connection lines arc not shown in the other embodiments for the sake of clearness but may also be present in other embodiments.

[0042] According to embodiments described herein, the term "the controller is connected to a device" is typically understood as "the controller is connected to a drive of the dev ice . For instance, the term "the controller is connected to the substrate buffer" may be understood as "the controller is connected to a drive of the substrate buffer". The substrate buffer may be configured to mov e up and down, thereby loading or unloading substrates onto or from the substrate buffer. This movement can be performed by a drive. The driv e may be connected to the controller. The driv e may be an electric motor, in particular a linear motor.

[0043] Similiar considerations may apply to the substrate loading stack arrangement. The term "the controller is connected to the substrate loading stack arrangement ^" may be understood as "the controller is connected to a drive of the substrate loading stack arrangement". The substrate loading stack arrangement may be configured to move up and down, thereby loading or unloading substrates onto or from the substrate loading stack arrangement. This movement can be performed by a driv e. The driv e may be connected to the controller.

[0044] Similar considerations may apply to the drives of the transport devices. A typical transport device as used herein is a conv eyor, such as a conv eyor belt, as shown in the figures. The conveyor belt may include one centrally arranged belt, or the conv eyor belt may include two belts with each of the belts arranged off-central. Alternatively or additionally, a gripper or a substrate support, on which the substrate rests while the substrate support is moved, can be employed. The at least one transport devices may be equipped with a driv e, e.g. one drive for each transport device. The drive of the transport device can be selected from the group consisting of a linear motor, a belt-driven motor, a pneumatic device, and any combination thereof. The term "the controller is connected to the first, second or third transport device" may be understood as "the control ler is connected to the driv e of the first, second, or third transport dev ice". [ 0045] According to embodiments, the controller is configured to synchronize the movement of two or more of the following devices: The substrate loading stack arrangement, the substrate buffer, the transport devices, and the one or more processing stations. Normally, the term "synchronize" does not mean that the respective elements operate at the same rate. Rather, the term "synchronize" shall describe an aligned operation of the substrate loading stack arrangement, the substrate buffer, the transport devices, and the one or more processing stations. [0046] So as to allow the substrate loading stack arrangement to unload substrates from the substrate loading stack arrangement onto the conveyor, and/or to allow the substrate buffer to load and unload substrates onto and from the conveyor, the conveyors, according to the present disclosure, may consist of two or more separate belts and/or may have a width which is smaller than the substrate to be transported. If two or more separate belts are provided, the belts are typically arranged parallel to each other. The substrate loading stack arrangement and the substrate buffer, respectively, may be positioned such that the substrate loading stack arrangement and the substrate buffer, respectively, can grip a substrate which rests on the conveyor. For instance, if in such a situation the substrate buffer is lifted, the substrate is lifted along and is accommodated in the substrate buffer's tray. In other positions of the substrate buffer, the substrates can pass through the substrate buffer, on the conveyor, without contacting any part of the substrate buffer.

[0047] According to typical implementations, the present embodiments are used for the manufacture of solar cells. The substrates may be quadratic (with or without rounded corners) and may have a ma imum size of 20cm x 20cm, more typically the substrate may have a size of approximately 15.6cm x 1 5.6cm.

[0048] The first, second and/or third transport devices, according to embodiments described herein, such as conveyor belts, may include one or more underpressure zones. One or more underpressure zones may be particularly useful at the location of the one or more processing stations. For instance, if material is printed on the substrate, it may be beneficial that the substrate's position is fixed.

[0049] As disclosed herein, the substrate loading stack arrangement when mounted on the reception of the apparatus for processing substrates is typically fully loaded with substrates that are supposed to undergo various processing actions so as to manufacture solar ceils. The multitude of substrates are subsequently moved out from the substrate loading stack arrangement by a transport device, such as a conveyor. The rate at which the substrates are discharged from the substrate loading stack arrangement is called "first rate" herein. According to embodiments, the first rate is between 0.2 substrates per second and 1 .0 substrates per second. Notably, the terms "unloading the substrates", "discharging the substrates", "emptying the substrates" etc. are used synonymously herein and refer to taking the substrates out from the substrate loading stack arrangement, or the substrate buffer, typically by a transport device on which the substrates may subsequently be transported.

[0050] As described, according to aspects of the present embodiments, only a fract ion of the multitude of substrates in the substrate loading stack arrangement is used for immediate processing whereas the other fraction is temporarily stored in a substrate buffer. According to implementations, the fraction used for immediate processing may be 50% of the multitude of substrates, and the fraction temporarily stored in the substrate buffer may be 50% of the multitude of substrates. The term "immediate" processing can be understood in that the substrate is unloaded from the substrate loading stack arrangement and directly led to a processing station by one or more transport devices. "Immediate" processing, or synonymously "directly leading a substrate to the processing station" can be understood in contrast to temporarily buffering substrates in the substrate buffer. For instance, the substrate loading stack arrangement when mounted to the apparatus for processing substrates may include 100 substrates. Subsequently, to unload the substrates from the substrate loading stack arrangement, 50 substrates from the 100 substrates may be stored in a substrate buffer, and 50 substrates may be directly fed to the processing station. In such a case, the first rate is two times the second rate at which the substrates are buffered, and at which the substrates may then be processed.

[005 1 ] In other embodiments, other fractions are employed. For instance, if unloading from the substrate loading stack arrangement can be accomplished at an essentially higher speed as compared to the smallest maximum speed of the one or more processing stations, the fraction of substrates stored in a substrate buffer can be larger than 50%, e.g. 2/3. In other words, in such an embodiment, two of three substrates unloaded from the substrate loading stack arrangement are buffered whereas only one out of three substrates unloaded from the substrate loading stack arrangement is directly led to a processing station. This may be beneficial where the processing speed is essentially more restricted than the unloading speed technically possible. Additionally or alternatively, it may allow for more time for the exchange of the substrate loading stack arrangement.

[0052] This is a specific example for the general embodiment encompassed herein that the second rate at which the substrate buffer is loaded differs from the processing rate of the one or more processing stations of the apparatus. Further, as it is also the case in this specific example, the second rate at which the substrate buffer is loaded may differ from the rate at which the substrate buffer is unloaded when it is full according to embodiments described herein. More specifically, if more than half of the substrates unloaded from the substrate loading stack arrangement are stored in the substrate buffer, the rate for unloading the substrate buffer is typically smaller than the rate at which the substrate buffer is loaded (called "second rate" herein ). Without limitation to any embodiment, the rate at which the substrate buffer is unloaded typically is smaller than the processing speed/rate of the apparatus for processing substrates as disclosed herein.

[0053] According to another example of the present disclosure, the fraction of substrates stored in a substrate buffer can be smaller than 50%, e.g. 1/3. In other words, in this example, only every third substrate is buffered whereas two out of three substrates unloaded from the substrate loading stack arrangement are directly led to a processing station. In such a case, the unloading rate of the substrate buffer is larger than the loading rate, i.e. the second rate. [0054] The rate at which the substrate buffer is filled with substrates is called the second rate herein. The second rate may be between 0.5 substrates per second and 1 .5 substrates per second. The second rate is smaller than the first rate.

[0055] According to embodiments, the second rate is half (i.e. 1/2) of the first rate. This corresponds to a situation where every second substrate unloaded from the substrate loading stack arrangement is picked up by the substrate buffer for temporary storage of the substrate. More generally, i a fraction of 1/n of the multitude of substrates with 0<l/n<l is buffered in the substrate buffer and 1 - 1 n of the multitude of substrates is directly processed, this corresponds to the feature that the second rate is 1/n of the first rate.

[0056 ] Once the substrate loading stack arrangement is empty, it is normally replaced by a fully loaded substrate loading stack arrangement (called the "new" substrate loading stack arrangement herein ). During the exchange time of substrate loading stack arrangement, according to embodiments, the processing of substrates is uninterrupted.

More specifically, substrates from the substrate buffer are unloaded onto the processing line for undergoing processing in one or more processing stations during times of no substrate supply. According to embodiments, the unloading of substrates from the substrate buffer is done at the first rate. This is beneficial in that the rate of the processing line is not to be altered once the substrate loading stack arrangement is empty and the further supply of substrates is accomplished by the substrate buffer. Thus, according to typical embodiments described herein, unloading substrates from the substrate buffer starts at the time when the substrate loading stack arrangement is empty.

[0057 ] Embodiments of the present disclosure allow for a continuous solar cell production with only one position for solar cell substrate loading using a substrate loading stack arrangement. Replacement of the substrate loading stack arrangement is no longer an operation critical to the overall production time. [0058] In typical embodiments, the number of trays and/or height of the substrate loading stack arrangement is twice the number of trays and/or height of the substrate buffer.

[0059] As e emplariiy shown in the figures, the apparatus for processing substrates according to embodiments described herein may include more than one transport dev ice. In particular, a first transport dev ice, e.g. a first conveyor, may be positioned at the substrate loading stack arrangement and/or the substrate buffer. A second transport device, e.g. a second conveyor, may be provided directly downstream of the first transport dev ice. A third transport dev ice, e.g. a third conveyor, may be positioned directly downstream of the second transport device. The third transport device might be configured to transport the substrate to and/or from a processing station for being processed. The terms "upstream" and "downstream" as used herein refer to the processing direction of the substrates, i.e., in the exemplary figures from left to right.

[0060] In the illustrations of Figs. I to 6, the first transport dev ice is illustrated as a conveyor and denoted with reference number 3, the second transport device is illustrated as a second conveyor and denoted with reference number 4, and the third transport dev ice is illustrated as the third conveyor and denoted with reference number 5. As shown in these figures, the third transport dev ice transports the substrates under the processing station 6. For instance, the processing station 6 may be a printing station for printing conductive paths on the substrates, e.g. so-called fingers and/or bus bars. Typically, the third transport device is configured to maintain the substrate while it is being processed, for instance, while the conductive layers are printed thereon. Alternatively, the substrates may be accommodated on the third transport device while an adhesive is printed thereon, while the substrates are scribed and/or while the sustrates are cleaved.

[0061] A possible implementation of a conveyor as used herein is a so-called printing nest. The use of a printing nest is particularly interesting for the one or more transport dev ices that transport the substrate under, or into, the processing station. In the examples of Figures 1 -6, this corresponds to the third transport device 5. According to embodiments, the substrate is held by the printing nest while the processing takes place, in particular by the application of underpressure.

[0062] In Fig. 7, an example of a printing nest is illustrated. The printing nest 131 may include a conveyor assembly 139 that may have a feed spool 135, a take-up spool 13 , rollers 140 and/or an actuator 148. The actuator 148 is typically coupled to the feed spool 135 and/or take-up spool 136. A substrate supporting surface 138 may be prov ided on which a conveyor beitconveyor belt 137 can be moved. The substrates are typically moved along with the conveyor beitconveyor belt to the processing station, and/or from the processing station.

[0063] According to embodiments, the conveyor belt is not an endless belt. During a processing action, such as a screen printing action, in processing station 6, the substrate may be positioned on the conveyor belt 137. The conveyor belt may be a porous material that allows substrate 10 to be firmly retained on the supporting surface 138, e.g., by applying an underpressure from below the conveyor belt 1 37. Specifically, the conveyor belt may be made of a disposable material, such as paper.

[0064] In one configuration, the drive 148 may be coupled to the feed spool 135 and/or the take-up spool 136 (e.g. by a drive wheel 147) so that the movement of substrate 10 positioned on the conveyor belt 137 can be accurately controlled within the printing nest 1 3 1 . The drive may be connected to the controller as described herein.

[0065 ] In implementations, the substrates are delivered from the first transport dev ice, e.g. the first conveyor, to the second transport device, e.g. the second conveyor, and from there to the third transport device, e.g. the thi d conveyor. The transport speed of the third transport device may be higher than the transport speed of the first transport device. The second transport device may be used to accelerate the substrates from the speed of the first transport device to the speed of the third transport device. The transport speed of the third transport device may be x times the speed of the first transport device with x> 1 , in particular with x> 1 .5. [0066] As used herein, the wording "the rate of a first device is x times the rate of a second device , or "the speed of a first device is x times the speed of another device" shall describe a situation where the rate, or the speed, of the first device is higher in an amount corresponding to a multiplication of the rate, or the speed, of the second device by x. This shall particularly include deviations of at least +/-20%, in some embodiments only a deviation of +/-10%, and in particular embodiments no deviation at all.

[0067] Consequently, and not limited to any embodiment, the second transport device may be acting as a speed change device. This shall be understood in that the transport speed of the transport device positioned directly upstream of the speed change device is different from the transport speed of the transport device positioned directly downstream of the speed change device. For instance, the transport speed of the transport device positioned directly upstream of the speed change dev ice may be smaller than the transport speed of the transport device positioned di ectly downstream from the speed change device.

[0068] For instance, the transport speed of the first transport device may be in the range of 1 50-500 mm/s (e.g., 350 mm/s), and/or the transport speed of the third transport device may be in the range of 500- 1 .000 mm/s (e.g., 700 mm/s). The transport speed of the second transport device may vary between these values.

[0069] In embodiments, the transport speed of the first transport device may be between 33% and 66% of the transport speed of the third transport device (e.g., approximately 50%).

[0070] Fig. 8 illustrates the method according to embodiments described herein. The method for processing substrates includes the block 201 according to which a substrate loading stack arrangement is provided. The substrate loading stack arrangement includes a multitude of substrates. Substrates are unloaded from the substrate loading stack arrangement at a first rate in block 202. The substrate buffer is filled with substrates from the substrate loading stack arrangement at a second rate in block 203. The second rate is smaller than the first rate.

[0071 ] While the foregoing is directed to embodiments of the disclosure, other and further embodiments of the disclosure may be devised without departing from the basic scope thereof, and the scope thereof is determined by the claims that follow.