WO2015124191A1

WO2015124191A1 - Solar cell processing system, conveyor belt system, solar cell production installation and method

Info

Publication number: WO2015124191A1
Application number: PCT/EP2014/053352
Authority: WO
Inventors: Davide PIZZOLATO; Daniele Andreola
Original assignee: Applied Materials Italia S.R.L.
Priority date: 2014-02-20
Filing date: 2014-02-20
Publication date: 2015-08-27
Also published as: CN106062974A; TW201541659A; EP3108508A1

Abstract

A processing system for producing solar cells is provided. The processing system includes a conveyor belt system. The conveyor belt system includes a conveyor belt for transporting a solar cell wafer. Furthermore, the processing system includes a laser unit configured to direct a laser beam onto the solar cell wafer during transportation of the solar cell wafer by the conveyor belt. Furthermore, a conveyor belt system for use in the production of solar cells is provided that includes a support surface with several openings in the support surface; a conveyor belt with several openings in the conveyor belt; and a first underpressure circuit connected to at least a part of the multitude of openings in the support surface. Furthermore, a method for producing solar cells is provided. The conveyor belt system includes transporting a solar cell wafer; and, during transporting, directing a laser beam to the solar cell wafer.

Description

SOLAR CELL PROCESSING SYSTEM, CONVEYOR BELT SYSTEM, SOLAR CELL PRODUCTION INSTALLATION AND METHOD

FIELD OF THE INVENTION

[0001 ] Embodiments of the present disclosure relate to a solar cell processing system for producing solar cells, a conveyor belt system for use therein, a solar cell production installation and a method of producing solar cells. In particular, embodiments of the present disclosure relate to a solar cell processing system for producing passivated emitter rear contact (PERC) solar cells, a conveyor belt system for use therein, a solar cell production installation configured for producing PERC solar cells, and a method of producing PERC solar cells.

DESCRIPTION OF THE RELATED ART

[0002] Solar cells are photovoltaic (PV) devices that convert sunlight into electrical power. A typical solar cell includes a substrate that may also be called wafer herein. The wafer is typically made of silicon. The wafer may be provided with one or more p-n or p-i-n junctions formed therein. Each p-n junction has a p-type region and an n-type region. When the p-n junction is exposed to sunlight, i.e., if an incoming photon is absorbed, it can lead to the excitation of an electron from the valence band to the conduction band of the solar cell, thereby forming a so-called electron-opening pair where both electrons and openings act as charge carriers. The electrical field developed in the junction allows the charge carriers to be separated and to drift in opposite directions. If the emitter and the base are connected by the so-called electrodes, such as made of silver or aluminum, the charge carriers can be used as electric energy.

[0003] Solar cells are commonly formed from silicon substrates, which can be monocrystalline or multi-crystalline silicon substrates. The silicon substrate may have a thin layer of n-type silicon on the front side with a p-type zone formed on the backside. Alternatively, the silicon substrate may have a thin layer of p-type silicon on the front side with an n-type zone formed on the backside (so-called "n-type wafer"). Electrodes are deposited on the solar cell wafer and need to be contacted to the silicon. Additional layers such as anti-reflection layers on the front side, or reflection layers on the backside may furthermore be provided. Notably, as understood herein, the term "solar cell" refers to the completed solar cell (i.e., the solar cell that is functional) whereas the term "solar cell wafer" refers to the semiconductor wafer during its process of becoming a solar cell.

[0004] The present disclosure particularly relates to the production of passivated emitter rear contact (PERC) solar cells. Therefore, for the present disclosure, the non- illuminated side of the solar cell, i.e. the back side of the solar cell wafer, is of particular interest. A layer of aluminum is often used that covers the entire back side of the solar cell.

[0005] Since electron-opening pairs tend to recombine shortly after having been formed, and since the recombination phenomenon is particularly critical on the surfaces of the wafer, the passivation of the wafers by dielectric layers is known to provide solar cells with higher efficiencies. It minimizes the recombination phenomena and thereby increases the lifetime of charge carriers before they recombine. This, in turn, optimizes the energy efficiency of the solar cell which is most essential as it increases the return on investment for the solar cell customers.

[0006] Evidently, when the back side of a solar cell wafer is covered with a layer of dielectric material, an electrical contact must be established therethrough. In a known method (called "laser ablation"), the back side of a solar cell wafer is contacted by applying first a passivating dielectric coating, and in a subsequent processing station, by locally opening the dielectric using a laser. Afterwards, an aluminum layer is applied over the entire area for contacting the back side, possibly after heating the wafer.

[0007] However, solar cell production industries are subject to enormous price pressure. The governing number is the throughput of a solar cell processing system in terms of number of wafers produced per hour (wph). Each additional process step such as the described opening of the dielectric using a laser reduces the numbers of wafers per hour, though. SUMMARY OF THE INVENTION

[0008] As found out by the inventors of the present disclosure, the present solar cell production can still be improved.

[0009] In view of the above, the present disclosure provides the following.

[0010] According to an aspect of the present disclosure, a processing system for producing solar cells is provided. The processing system includes a conveyor belt system. The conveyor belt system includes a conveyor belt for transporting a solar cell wafer. Furthermore, the processing system includes a laser unit configured to direct a laser beam onto the solar cell wafer during transportation of the solar cell wafer by the conveyor belt.

[0011 ] In particular, the conveyor belt system of the processing system may be a conveyor belt system as described in the remainder of the specification.

[0012] According to a further aspect of the present disclosure, a conveyor belt system for use in the production of solar cells is provided. The conveyor belt system includes a support surface with several openings being located in the support surface; a conveyor belt with several openings being located in the conveyor belt; and a first underpressure circuit connected to at least a part of the multitude of openings in the support surface.

[0013] According to a further aspect of the present disclosure, a solar cell production apparatus is provided. The solar cell production installation includes a processing system as described herein and/or a conveyor belt system as described herein.

[0014] According to a further aspect of the present disclosure, a method for producing solar cells is provided. The conveyor belt system includes transporting a solar cell wafer; and, during transporting, directing a laser beam to the solar cell wafer. [0015] The disclosure is also directed to an apparatus for carrying out the disclosed methods and including apparatus parts for performing each described method steps. These method steps 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, the disclosure is also directed to methods by which the described apparatus operates. It includes method steps for carrying out every function of the apparatus.

[0016] Further embodiments, aspects, details and advantages are furthermore evident from the dependent claims, the description, and the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0017] 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:

[0018] Fig. 1 illustrates a schematic cross-sectional view of an excerpt of a solar cell produced according to embodiments described herein.

[0019] Fig. 2 illustrates a schematic cross-sectional view of an excerpt of a solar cell wafer during the production according to embodiments described herein.

[0020] Figs. 3 and 4 are schematic views of solar cell processing apparatuses according to embodiments described herein.

[0021 ] Fig. 5 is a schematic three-dimensional view of a conveyor belt system according to embodiments described herein. [0022] Fig. 6 is a schematic three-dimensional view of a conveyor belt system according to embodiments described herein wherein, for illustrative purposes, the conveyor belt is omitted.

[0023] Fig. 7 is a schematic three-dimensional view of a conveyor belt system according to embodiments described herein in a bottom view.

[0024] Fig. 8 is a schematic three-dimensional view into the conveyor belt system according to embodiments described herein.

[0025] Figs. 9 and 10 are three-dimensional views of processing systems according to embodiments described herein.

DETAILED DESCRIPTION OF EMBODIMENTS

[0026] Reference will now be made in detail to the various embodiments of the invention, one or more examples of which are illustrated in the figures. Within the following description of the drawings, the same reference numbers refer to same components. In the present disclosure, only the differences with respect to individual embodiments are described. Each example is provided by way of explanation of the invention and is not meant as a limitation of the invention. 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.

[0027] With reference to Figs. 1 and 2, a cross-sectional view of a solar cell that could be produced with the processing system, the solar cell production installation and method as described herein is shown. The cross-sectional view is not true to scale but shall only illustrate the sequence of the layers in the solar cell.

[0028] The solar cell 10 includes several layers. The uppermost layer on the front side of the solar cell (the upper side in the illustration of Figs. 1 and 2) can be an antireflection layer 6 configured and deposited for reducing the reflection of sunlight. Below is the bulk layer 1 which is typically doped silicon. The bulk layer is typically the thickest layer. Various types of doping can be included in the bulk layer 1 , as discussed in the background part.

[0029] Two passivation layers are shown, namely, the first passivation layer 2 and the second passivation layer 3. The one or more passivation layers that are provided according to the present embodiments are made of dielectric material. For instance, the first passivation layer may be made of AI203 (aluminumoxide), and/or the second passivation layer may be made of SiN (siliconnitride). It is typical that the passivation layers cover the entire bulk layer from the back of the solar cell wafer.

[0030] According to embodiments described herein, after the provision of a solar cell wafer that is passivated on the back side, local openings are formed using a laser beam. This is illustratively shown in Fig. 1 which illustrates an intermediate process step in the production of a solar cell according to embodiments described herein. As illustrated therein, the passivation layers 2 and 3 are ablated by a laser unit 15 to produce vias 7 in the one or more passivation layers. Thereby, an access to the bulk layer is thus produced.

[0031 ] In a subsequent step, with reference to Fig. 2, the back side layer is deposited. The layer referred to with reference number 4 illustrates the back side contacting layer made of a conductive material. The back side contacting layer 4 is typically deposited over the entire back side of the solar cell 10, and allows contacting the solar cell wafer from the back.

[0032] In particular, the deposition of the back side layer produces not only the back side contacting layer 4 but also a filling 5 of the vias 7 (Fig. 1 ). Thereby, the contact between the bulk layer 1 of the solar cell wafer and the back side contacting layer (i.e., the back side electrode) is accomplished which allows a current to flow when the solar cell is in operation. In addition, it turns out that the local contact fillings 5 in the dielectric passivation layers 2 and 3 also reduce the number of recombinations at or close to the boundary surface. [0033] Fig. 3 shows a schematic embodiment of a processing system for producing solar cells according to the present disclosure. The processing system 100 includes a conveyor belt system 20. The conveyor belt system is provided with a conveyor belt for transporting solar cell wafers. In Fig. 3, the solar cell wafers are denoted with reference number 21 . For illustrative purposes, one solar cell wafer is shown before the laser ablation, one solar cell wafer is shown during laser ablation and one solar cell wafer is shown after the laser ablation. The movement direction of the conveyor belt is illustrated with arrow 60.

[0034] The laser ablation is carried out by the laser unit 15 that is configured to direct a laser beam 18 onto the solar cell wafers 21 , for instance generated by the laser light source 16, while the solar cell wafers are transported by the conveyor belt. Hence, the conveyor belt does not stop to direct the laser beam to the solar cell wafer but the laser ablation process as understood herein is an "on the fly" process.

[0035] Referring now to Fig. 4, another embodiment of the present disclosure is illustrated. The processing system shown includes, further to the elements explained already with respect to the embodiment of Fig. 3, a processing station 32. In particular, the processing station 32 may be a vacuum processing station wherein the processing of the wafer takes place in an underpressure atmosphere, such as medium or high vacuum. For instance, the processing station may be a passivation station wherein the back side of the solar cell wafer is passivated with one or several dielectric layers, such as AI203 or SiN. In many embodiments, the number of processing stations upstream of the laser unit is more than one, such as at least three or even five.

[0036] An incoming conveyor belt system 31 may be positioned upstream of the conveyor belt system 20 wherein the term "upstream" and "downstream" as used herein shall be understood in terms of the movement of the solar cell wafers. The incoming conveyor belt system 31 is not necessarily a conveyor belt system as described herein, however, it can be such a conveyor system.

[0037] Additionally, or alternatively, it is possible that one or more further processing stations are located downstream of the laser unit 15. For instance, a further processing station 34 is illustrated in Fig. 4. It may be a printing station where the back side contacting layer, e.g. made of aluminum, is deposited over the solar cell wafers. The solar cell wafers whose backside were ablated by the laser unit 15 may be transported by another outgoing conveyor belt system 33 to be processed in the further processing stations, such as processing station 34. The further processing station may operate in an ambient pressure atmosphere. In particular, at least one of the further processing stations may be a printing station.

[0038] Fig. 5 illustrates is a schematic view of a conveyor belt system 20 according to embodiments described herein. The conveyor belt system 20 may generally include one or more conveyor belts. In the embodiment illustrated in Figs. 5 to 8, the conveyor belt system includes two conveyor belts 50 that are arranged in parallel. The two conveyor belts 50 may be distanced from each other by between 3 cm and 15 cm, in particular by between 5 cm and 10 cm.

[0039] The one or more conveyor belts according to the present disclosure typically include a multitude of openings 51 . The openings may be arranged in an array-like manner. As illustrated in the embodiment of Fig. 5, each conveyor belt 51 may be provided with a line of openings 51 . The openings are typically positioned in an equidistant manner. The openings may be spaced apart from each by a distance from typically between 0.5 cm and 10 cm, in particular from between 1 cm and 5 cm.

[0040] Although not shown in the embodiment of Fig. 5, several openings on a conveyor belt may be arranged next to each other in parallel (i.e., in a direction perpendicular to the transport direction 60). Not limited to any embodiment, the openings of the one or more conveyor belts are typically circular and may have a diameter of between 1 mm and 2 cm, in particular of between 2 mm and 1 cm.

[0041 ] The conveyor belt may be driven by an actuator, such as an electric motor or servo motor. The actuator is hardly recognizable in the view of Fig. 5 because it is hidden behind the plate 54. The actuator 58 may work directly on one of the two rotation axes 59 of the conveyor belt system 20. Alternatively, as it is illustrated in Figs. 5 and 6, the actuator may work indirectly on one of the two rotation axes 59, e.g. by driving an axis 53 of an indirect actuator unit 57, the motion of which is transferred to a rotation axis 59 of the conveyor belt system.

[0042] The length of the conveyor belt system, i.e. the extension of the conveyor belt system in the transportation direction 60, is typically more than 20 cm and in various embodiments even more than 50 cm.

[0043] The one or more conveyor belts according to the present disclosure run over a support surface 61 of the conveyor belt system 20. The support surface 61 will be illustrated in further detail in view of the embodiment shown in Figs. 6 and 8.

[0044] The conveyor belt system 20 according to embodiments described herein may include a first underpressure zone 55 and a second underpressure zone 56. The underpressure zones will be explained in further detail with respect to Figs. 6 and 7. Typically, the first underpressure zone is at least 1.5 or even 2.0 times as long as the second underpressure zone in the transport direction of the conveyor belt system

[0045] Referring to the embodiments illustrated in view of Fig. 6, the conveyor belt system 20 is shown without a conveyor belt for illustrative purposes. Evidently, in operation of the conveyor belt system 20, one or more conveyor belts are provided, such as shown in Fig. 5.

[0046] The conveyor belt system 20 includes the support surface 61. The support surface is configured to allow the conveyor belt to run over it. The support surface may be made of a low friction material, such as low friction plastic material. In embodiments, the support surface may be provided with one or more runways 62. In the embodiment illustrated in Fig. 6, but not limited thereto, two runways are provided. Each runway is typically configured to allow a conveyor belt to run over it during operation. The runway may have a smaller width than the conveyor belt has, for instance, the width may be at least 10% smaller than the width of the conveyor belt.

[0047] In other embodiments, three or even four runways may be provided. Generally, and not limited to any embodiment described herein, a runway may be elevated over the support surface. For instance, the one or more runways of the present disclosure may be elevated by at least 1 mm. In embodiments, the runway is made of a low friction material, such as low friction plastic material. The runway may be made of the same material as the support surface.

[0048] Not limited to the embodiment illustrated in Fig. 6, the support surface is typically provided with one or more openings 63, 64. Where runways are provided, the openings 63, 64 may also lead through the runways, as illustrated in Fig. 6. The openings are typically arranged at locations where the conveyor belt is supposed to run. The openings of the support surface lead to one or more underpressure circuits located embedded in the conveyor belt system. The one or more underpressure circuits are typically adapted to provide underpressure.

[0049] The conveyor belt system of the processing system according to the present disclosure is typically located in an ambient atmosphere. The underpressure provided by the underpressure circuits exerts a suction force on the solar cell wafers via the openings 63, 64 in the support surface, possibly through the one or more runways 62, if any, and via the openings 51 in the one or more conveyor belts 50.

[0050] The openings 63 of the embodiment illustrated in Fig. 6 belong to the first underpressure zone 55 whereas the openings 64 belong to the second underpressure zone 56. The openings 63 are in fluid connection with a first underpressure circuit and the openings 64 are in fluid connection with a second underpressure circuit. Providing two different underpressure circuits and zones allows the application of different suction forces to the solar cell wafers in the respective zones.

[0051 ] For instance, in typical embodiments, the underpressure in the first underpressure zone is smaller (i.e., the pressure in terms of mbar is higher) than the underpressure in the second underpressure zone (i.e., the pressure in terms of mbar is smaller in the second zone). Where the provided underpressure is smaller, also the suction force is smaller as compared to a zone with a larger underpressure.

[0052] In possible applications, it may not be necessary that the position of a solar cell wafer is fixed with respect to the conveyor belt as exactly as it may be required in the second zone. For instance, the second underpressure zone may be the zone where the actual bombardment with a laser beam takes place, whereas the first underpressure zone may be used for transporting the solar cell wafers.

[0053] As illustrated in Fig. 6, the openings 63, 64 of the support surface may extend through the one or more runways, if provided.

[0054] The conveyor belt system may be provided with one or more sensor openings 74 that are typically arranged in support surface 61 , in particular in the middle of the support surface 61. For instance, the sensor openings allow the provision of one or more sensors (not shown) configured to sense the solar cell wafer position. The one or more sensors may be positioned on the back side of the conveyor belt system. The information of the sensors may be transmitted to a control unit that may control the alignment and/or the laser. For instance, the information of the one or more sensors may be forwarded to the control unit that is comprised in the laser unit 15, see further details below with respect to Figs. 9 and 10.

[0055] Fig. 7 illustrates in a schematic three-dimensional view the back side of a conveyor belt system according to embodiments described herein. The drawing shall primarily illustrate that the conveyor belt system may be provided with two underpressure connection inlets for the provision of underpressure. The first underpressure connection inlet is referred to by reference number 70, and the second underpressure connection inlet is referred to by reference number 71 .

[0056] The first underpressure connection inlet leads to the first underpressure circuit, and the second underpressure connection inlet leads to the second underpressure circuit. In operation, it is typical that the first underpressure inlet and/or the second underpressure inlet are connected to one or more underpressure provision units (not shown), such as one or more vacuum pumps or underpressure tanks. Also, it may be possible that only one underpressure provision unit is provided, which may for instance provide the second underpressure, and the reduced underpressure for the first underpressure may be provided by a valve connection of the first underpressure circuit with the underpressure provision unit. [0057] Fig. 8 is a further three-dimensional schematic illustration of an embodiment of a conveyor belt system according to embodiments described herein. The conveyor belt system 20 is shown without the conveyor belt for illustrative purposes. Furthermore, the conveyor belt is shown without the support surface or the runways as illustrated in Fig. 6. The open view into the conveyor belt system of Fig. 8 allows a deeper understanding of the underpressure circuits of the present disclosure.

[0058] The conveyor belt system illustrated in Fig. 8 is provided with two underpressure connection inlets 70 and 71 as explained in view of Fig. 7. In the view of Fig. 8, they are seen from the upside of the conveyor belt whereas they are shown from below in the illustration of Fig. 7. Generally, and not limited to the present embodiment, an underpressure connection inlet of the present disclosure typically leads to an underpressure circuit embedded in the conveyor belt system. For instance, the underpressure circuit may be a tube system buried in the conveyor belt system.

[0059] According to embodiments described herein, the conveyor belt system may be provided with a first underpressure circuit and a second underpressure circuit. The first underpressure circuit is denoted with reference number 80 in the illustrated embodiments of Fig. 8, and the second underpressure circuit is denoted with reference number 81. The first underpressure circuit 80 is typically in fluid connection with the first underpressure connection inlet 70, and the second underpressure circuit 81 is typically in fluid connection with the second underpressure connection inlet 71 .

[0060] As illustrated, the one or more underpressure circuits as provided according to embodiments described herein typically include a cross channel, such as the two cross channels 82 and 83 illustrated in Fig. 8. The term "cross" shall refer to the orientation of the cross channels that is substantially perpendicular to the transport direction 60 (for a typical understanding of the term "substantially" please see previous explanation).

[0061 ] A cross channel typically provides the underpressure to one or more longitudinal channels. A longitudinal channel is typically oriented in the transport direction 60. As illustrated in Fig. 8, each underpressure circuit may be provided with two longitudinal channels 84 and 85. Generally, and not limited to any embodiment, the channel system of each underpressure circuit may have a double-T shape.

[0062] In some embodiments, which can be combined with other embodiments described herein, as illustrated by the first underpressure circuit 80 of the embodiment of Fig. 8, the cross channel 82 may be provided centered with respect to the longitudinal channels 84. In other embodiments, as illustrated by the second underpressure circuit 81 of the embodiment of Fig. 8, the cross channel 83 may be provided off-centered with respect to the longitudinal channels 85.

[0063] The width of the cross-channel may be larger than the width of the longitudinal channels, in particular, there may be a factor of 2, 3, or even more than 3 between the width of the cross channels and the width of the longitudinal channels.

[0064] In embodiments, the length of the first underpressure circuit and/or of the second underpressure circuit in the transportation direction is in the range of between 10 and 50 cm, in particular in the range of between 10 and 30 cm..

[0065] The channel system of the one or more underpressure circuits of the present disclosure is typically buried in the conveyor belt system. The underpressure is transferred to the solar cell wafers via the openings 63, 64 in the support surface 61 and/or runways 62 as well as the openings 51 in the one or more conveyor belts 50. The provision of a first and second underpressure circuit allows different suction forces acting on the solar cell wafers in different zones.

[0066] Fig. 9 and 10 show schematic three-dimensional views of a processing system 100 according to embodiments of the present disclosure. Without limitation to any embodiment, the processing system may be equipped with an incoming conveyor belt system 31 . The conveyor belt system 20 is positioned downstream of the incoming conveyor belt system. The conveyor belt system 20 may be equipped with a first underpressure circuit and a second underpressure circuit, resulting in the first underpressure zone 55 and the second underpressure zone 56. Generally, and not limited to the embodiment of Figs. 9 and 10, the second underpressure zone 56 may be located below the laser unit 15.

[0067] Generally, and not limited to the embodiment of Figs. 9 and 10, the first underpressure is smaller than the second underpressure. The first underpressure is typically selected such that it allows the solar cell wafers to adhere to the conveyor belt during transportation. Typically, the solar cell wafer is not processed while it is in the first underpressure zone.

[0068] It is possible, though, that the solar cell wafer is aligned during movement in the first underpressure zone.

[0069] Such an alignment shall be illustrated by the alignment unit 91 that is shown above the conveyor belt system 20, in particular, above the first underpressure zone 55. Depending on the application, the alignment unit may be a non-controlled mechanical alignment, such as a narrowing path that pushes the wafer in a centralized position. Alternatively or additionally, the alignment unit as described herein may be configured for performing a controlled alignment, such as by measuring the actual position of the solar cell wafers, calculating the necessary re-alignment of the solar cell wafer, and performing the re-alignment individually, such as by a gripper.

[0070] Notably, in some embodiments, the position after alignment shall be kept exactly as it is for the processing by the laser tool. This may be one example as to why it may be beneficial that the second underpressure zone starts directly downstream of the alignment unit 91 .

[0071 ] The alignment unit may particularly include one or more cameras for sensing the actual position of the solar cell wafer. Furthermore, a picture analysis system may be provided that also allows evaluating the sensed pictures of the camera system. For instance, the outline of the solar cell wafers may be sensed in order to determine the actual position and orientation of the solar cell wafer. The picture analysis system may form part of a control unit as described herein. [0072] Generally, the alignment unit may perform an alignment step, as discussed before. However, it is also possible that the alignment unit merely measures the position of the solar cell wafer and provides the information about the position, for instance, to a laser control unit (not visible in Figs. 9 and 10 but it may be included in the laser unit 15). The information about the position of the solar cell wafers is thus taken into account in the control of the laser beam.

[0073] Furthermore, in the view of Figs. 9 and 10, the laser unit 15 is visible, and the laser 16 (Fig. 4) is located within the laser unit 15 and thus not visible. The laser typically includes a control unit configured to control the laser beam thereby particularly taking into account the transportation speed of the solar cell wafers. The laser is controlled such that a beam may be directed to the solar cell wafer, possibly in a pulsed manner. Furthermore, the laser beam may be guided directly to the solar cell wafers, or alternatively, the optical path of the laser beam may be deflected by one or more deflection units, such as one deflection mirror or several deflection mirrors (not visible in the view of Figs. 9 and 10 but they may be positioned within the laser unit 15).

[0074] An extractor fan unit 90 may furthermore be provided configured to suck the smoke generated due to the laser ablation process away. The extractor fan unit 90 has typically a box-like shape guaranteeing that the smoke is rather sucked away than emitted to the environment. In addition, the extractor fan unit may also be configured to avoid laser radiation to be emitted from the laser processing station to the environment. The extractor fan unit 90 is shaped such that it allows solar cell wafers to enter and exit the laser processing station.

[0075] Furthermore, as illustratively shown in Figs. 9 and 10, after ablation of the passivation layer with the laser beam, i.e. downstream of the conveyor belt system 20, an outgoing conveyor belt system 33 may be provided for further processing of the solar cell wafers. For illustrative purposes a further processing station 34 is illustrated.

[0076] As understood herein, a solar cell production installation may not only include the solar cell processing system as described and/or the conveyor belt system as described, in addition, it may include further processing units used in the production of solar cells, such as, one or more passivation stations for passivating the solar cell wafer, one or more printing stations for printing electrodes on the solar cell wafer, in particular on its front side, one or more flipping stations for flipping the solar cell wafer from one side to the other side (e.g., after processing the backside, flipping the solar cell wafer to the front side), one or more drilling stations for drilling small holes into the solar cell wafer (in particular in the case of the so-called Metal Wrap Through (MTW) solar cell production), one or more drying stations for drying printed material on the solar cell wafer, one or more doping stations for doping the solar cell wafer, one or more heating ovens for heating the solar cell wafer, one or more alignment stations for aligning the solar cell wafer, one or more testing stations for testing the functionality and/or optical appearance of the solar cell wafer, and/or one or more binning stations for binning the produced solar cells into quality and/or color groups. The indicated functionalities may likewise be included in embodiments of the method as described herein.

[0077] Embodiments of the method for producing solar cells as disclosed herein include transporting the solar cell wafer and, during transporting, directing a laser beam to the solar cell wafer. Notably, due to the fact that the ablation of the passivation layer by the laser beam is accomplished during transporting the solar cell wafer, no extra time is consumed. Therefore, the present disclosure allows for providing a solar cell production method with increased efficiency of the produced solar cells whereas throughput of the solar cell processing station is not reduced as compared to known solar cell processing stations. In other words, the throughput rate of wafers per hour is similar to a solar cell production process without ablation of the one or more passivation layers.

[0078] In typical embodiments of the method to produce solar cells, a solar cell wafer is doped. Afterwards, one or more passivation layers may be deposited on the back side of the solar cell wafer thereby typically covering the complete back side. In order to provide the contact to the doped region of the solar cell wafer, for instance the bulk layer 1 illustrated in Figs. 1 and 2, the laser beam is directed to the passivation layer. Typically, the laser control is configured to set the laser up to have sufficient energy to penetrate through the one or more passivation layers wherein, at the same time, the laser is typically controlled such that it does not intrude into the bulk silicon.

[0079] Typically, thereafter, the back contact is provided by depositing a conductive material, such as aluminum, silver, or a mixture of aluminum and silver, onto the back side of the solar cell (see explanation given with respect to Figs. 1 and 2). In embodiments, several layers of back contact may be provided. The solar cell wafer may then be flipped to process the front side, e.g., in order to deposit the front side contact.

[0080] In particular in the case of MWT solar cell production, the positioning of the vias 7 (Fig. 2) in the solar cell wafer requires increased preciseness. It is desired to avoid a collision of the vias 7 for contacting the bulk layer from the backside with the MWT through-holes in the solar cell wafers that are used in MWT solar cells for contacting the solar cell wafer from the front side. Hence, it is desired that the relative position between the laser and the solar cell should not vary during the processing. It is therefore beneficial to locally fix the solar cell wafers to the conveyor belt during the laser ablation by means of the underpressure as provided by the various embodiments described herein before in detail.

[0081 ] The present disclosure particularly includes retrofitting existing solar cell production apparatuses for producing solar cells with a processing system as disclosed herein and/or a conveyor belt system as described herein.

[0082] While the foregoing is directed to embodiments of the invention, other and further embodiments of the invention may be devised without departing from the basic scope thereof, and the scope thereof is determined by the claims that follow.

Claims

1. Processing system (100) for producing solar cells, the processing system

comprising:

a. a conveyor belt system (20), the conveyor belt system including a conveyor belt (50) for transporting a solar cell wafer (21 ); and

b. a laser unit (15) configured to direct a laser beam (18) onto the solar cell wafer (21 ) during transportation of the solar cell wafer by the conveyor belt (50).

2. Processing system according to claim 1 , wherein a multitude of openings (51 ) is

located in the conveyor belt (50).

3. Processing system according to any of the preceding claims, wherein the conveyor belt system further comprises:

a. a support surface (61 ), wherein a multitude of openings (63, 64) is located in the support surface; and optionally

b. a first underpressure circuit (80) connected to at least a part of the multitude of openings (63) in the support surface (61 ).

4. Processing system according to claim 3, further comprising a second underpressure circuit (81 ) connected to at least a part of the multitude of openings (64) in the support surface (61 ).

5. Processing system according to claim 4, wherein the second underpressure circuit (81 ) is connected to the multitude of openings that are positioned below the solar cell wafer while the laser beam (18) is directed to the solar cell wafer (21 ).

6. Processing system according to any of claims 3 to 5, further including one or more runways (62) configured for allowing the conveyor belt to run over, wherein the one or more runways (62) are elevated over the support surface (61 ).

7. Processing system according to any of the preceding claims, further comprising an alignment system (91 ) configured for detecting the solar cell wafer position.

8. Processing system according to any of the preceding claims, further comprising a deflection mirror positioned in the optical path of the laser beam.

9. Conveyor belt system (20) for use in the production of solar cells, the conveyor belt system comprising:

a. a support surface (61 ), wherein a multitude of openings (63, 64) is located in the support surface;

b. at least one conveyor belt (50), wherein a multitude of openings (51 ) is located in the at least one conveyor belt; and

c. a first underpressure circuit (80) connected to at least a part of the multitude of openings (63) in the support surface.

10. Conveyor belt system according to claim 9, further comprising a second

underpressure circuit (81 ) connected to at least a part of the multitude of openings (64) in the support surface (61 ).

1 1. Conveyor belt system according to any of the claims 9 to 10, further including one or more runways (62) configured for allowing the conveyor belt to run over, wherein the one or more runways (62) are elevated over the support surface (61 ).

12. Solar cell production installation including a processing system according to any of claims 1 to 8 and/or a conveyor belt system according to any of claims 9 to 1 1 .

13. Method for producing solar cells, the method comprising:

a. transporting a solar cell wafer (21 ); and

b. during transporting, directing a laser beam (18) to the solar cell wafer.

14. Method for producing solar cells according to claim 13, further comprising applying a first underpressure to the solar cell wafer.

15. Method for producing solar cells according to claim 14, further comprising applying a second underpressure to the solar cell wafer while directing the laser beam to the solar cell wafer, wherein the second underpressure is larger than the first underpressure.