Device for electrically connecting solar cells

Abstract

Device for electrically connecting solar cells (6), wherein a flat conductor is first connected to a solar cell (6) with a first functional assembly and several solar cells (6) are connected to form a solar cell string with a second functional assembly, wherein the first functional assembly has at least the following features: 1.1. a feed / cutting unit for the flat conductor, 1.2. a magazine unit for storing the solar cells (6), 1.3. a manipulator unit for positioning a solar cell relative to the flat conductor, 1.4. a first soldering unit with a first plasma source for generating a heat zone in which the flat conductor is at least partially melted and bonds with the solar cell, and 1.5. a pallet (4) for placing the processed solar cells.

Description

[0001] The invention relates to a device for electrically connecting solar cells.

[0002] Known methods for electrically connecting a solar cell to a flat conductor for use as part of a solar cell string utilize preheated conductor tabs or soldering irons with copper fingers to heat the joint. Infrared heat sources can also be used to generate the necessary process heat. However, all methods require the application of an electrical contact or flux to the joint in a measured dose and within a defined timeframe before the process begins.

[0003] Furthermore, it is known to use a plasma jet to deposit the electrical contact material on the solar cell. From publication WO 2014 / 033047 A1, a method for connecting conductors to substrates is known, wherein a plasma is generated and a connecting material is introduced into the plasma. The plasma with the connecting material is applied to the section of the substrate to be joined, so that a deposit of connecting material forms a metallurgical electrical connection between the conductor and the substrate. An alternative method for electrically connecting solar cells for a solar module is known, for example, from publication DE 10 2010 013 850 A1, in which an adhesive electrical connection between a conductor and the solar cell is created by depositing a contact material in the contact area of ​​the conductor and the solar cell using low-temperature plasma spraying.

[0004] In the methods known so far, a plasma is used as a heat source only in conjunction with an additional material, which is deposited on the solar cell as an electrical contact medium.

[0005] The object of the invention is to create an alternative device for the electrical connection of solar cells. This device is primarily intended to prevent the solar cells from slipping during the soldering process and to ensure rapid dissipation of the heat generated during soldering.

[0006] This problem is solved by the features of the independent claims. Advantageous embodiments of the invention are the subject of dependent claims.

[0007] The inventors have realized that it is possible to use plasma as a heat source for a type of soldering process to connect solar cells and flat conductors without the use and deposition of any additional contact or bonding material.

[0008] Based on this premise, the inventors have developed a two-stage device and a two-stage process. In a first step, a flat conductor can be attached to a solar cell using a first functional assembly of the device. The processed solar cell can then be placed at a defined distance on a pallet that moves forward incrementally. In a second step, the processed solar cells can be connected to each other to form a solar cell string using a second functional assembly of the device. According to the invention, a plasma jet is used as a heat source for connecting the flat conductor to the solar cell and for connecting the solar cells, with this process occurring without deposits under a protective gas atmosphere. This means that during the soldering process, only the flat conductor, conventionally made of a silver alloy, melts and bonds with the surface of the solar cell.

[0009] The main difference between the first and second plasma soldering process is that, in the first soldering process, the solar cell with the conductor to be connected is moved towards the stationary first soldering unit within the first functional assembly, while in the second soldering process, the second soldering unit moves within the second functional assembly.

[0010] Compared to conventional soldering methods, the use of the deposit-free plasma soldering process according to the invention offers the following advantages: - The required exposure time, i.e., the duration for which the plasma or heat acts on the components to be joined, is reduced from 1 to 2 seconds in conventional processes to 0.2 seconds. This allows for significantly shorter cycle times in manufacturing. The method according to the invention is fundamentally contactless, which prevents mechanical damage to the solar cell. This means that heat transfer occurs without contact via the plasma jet, which exerts virtually no pressure on the solar cell. However, it is necessary that the conductor rests on the solar cell with only a minimal solder gap. This is achieved by gently pressing the conductor against the solar cell. - The heat zone on the solar cell is much smaller than with other methods. Therefore, the risk of damaging the solar cell is lower. - Since the tungsten electrode of the soldering unit is protected from oxygen (oxidation) by means of inert or protective gas for generating the plasma jet, the maintenance intervals are significantly longer than with soldering finger processes. - The equipment required to carry out the process is significantly more cost-effective in terms of acquisition and maintenance with regard to energy consumption and wear parts than conventional methods. Conventional methods require a contact agent or flux. In the method according to the invention, the heating zone is located under a protective gas atmosphere. The electrical connection or contacting of the solar cell and the flat conductor occurs without the application of any additional contact agent or flux. This also reduces costs and contributes to environmental protection.

[0011] The inventors propose essentially the following steps for carrying out the inventive method using an inventive device: - Initialization: After starting, all components of the device are moved to a zero position to calibrate the starting position. - Positioning of the manipulator arm: In the first cycle, the manipulator arm rotates to the position of the cell magazine. - Cell pickup: The manipulator head extends, allowing the suction cups attached to the manipulator head to grip the foremost solar cell using a vacuum. The head then retracts the solar cell by approximately 0.6 mm to prevent damage from friction between the solar cells. - Transport to the soldering station: The manipulator arm moves the manipulator head together with the solar cell it has picked up to the soldering station. - Positioning at the soldering station: The manipulator arm rotates to the position of the soldering station. The manipulator head is extended to bring the solar cell upwards into the correct soldering position, so that the actual underside of the solar cell faces upwards towards the flat conductor. - Ladder feed: The ladder feed positions the ladder flag (flat ladder) to the required length. - Pressure on the conductor flag: The manipulator head extends until the solar cell makes contact with the clamp via the intermediate flat conductor. This creates a defined pressure, meaning the solar cell and the flat conductor are pressed against the clamp. - Protective gas supply: To protect the tungsten electrode (plasma source) and the melt pool from oxidation, argon gas is passed through the ceramic nozzle along the tungsten electrode and over the solar cell. The argon protective gas also aids heat dissipation. Welding process: The high-frequency ignition initiates the plasma arc (plasma beam) between the tungsten electrode and the flat conductor. The current is between 2 A and 20 A. The distance between the tungsten electrode and the solar cell is approximately 0.2 mm to 0.6 mm. The soldering current flows from the tungsten electrode via the flat conductor to the clamping device, to which the ground connection is attached. The plasma arc burns for approximately 0.2 seconds and heats the flat conductor in a very short time. - Component connection: A tinned silver conductor is used as the flat conductor. The tin on the flat conductor melts locally and fuses with the silver conductor on the solar cell. Due to the very short heat exposure time of the plasma arc and the rapid heat dissipation by the clamping device and the copper end plate, damage to the solar cell is prevented. - After completion of the soldering process: After the soldering process is finished, the conductor tab (protrusion) is cut off from the conductor feed. - Removal of the solar cell: The manipulator head retracts together with the solar cell and the welded-on flat conductor. - Transport to the conveyor position: The manipulator arm moves to the position of the conveyor belt. - Placement on a pallet on the conveyor belt: The manipulator head moves towards the pallet waiting below. A brief pressure pulse breaks the vacuum, causing the solar cell to separate from the head. The solar cell now rests on the pallet with its top side facing upwards. - Conveying the solar cells: The conveyor belt moves the pallet of solar cells one step further. - Return to starting position: The manipulator arm moves back to the magazine position and repeats the steps described above as often as desired.

[0012] The steps described above are used to connect the flat conductor to the solar cell.

[0013] The following steps can then be performed to connect several processed solar cells: - Pressing the conductor tab of a second solar cell onto a first solar cell: A soldering unit with a copper hold-down moves towards the conductor tab to be joined and presses the conductor tab onto the top of the adjacent solar cell. - Simultaneously, the solder joint is created through the plasma soldering process.

[0014] Accordingly, the inventors propose a device for electrically connecting solar cells, wherein a first functional assembly connects a flat conductor to a solar cell and a second functional assembly connects several solar cells to form a solar cell string, wherein the first functional assembly comprises at least: - a feed / cutting unit for the flat conductor, - a magazine unit for storing the solar cells, - a manipulator unit for positioning a solar cell relative to the flat conductor, - a first soldering unit with a first plasma source for generating a heat zone in which the flat conductor is at least partially melted and bonds with the solar cell, and - a pallet for placing the processed solar cells.

[0015] The feed / cutting unit is used to feed the flat conductor to the solar cell to be processed and to position it on the solar cell, as well as to cut the flat conductor to the desired length.

[0016] The magazine unit stores the solar cells to be processed. Using the manipulator unit, the solar cell to be processed can be removed from the magazine unit and placed in the necessary position for the processing operation.

[0017] In one embodiment, the manipulator unit has a manipulator arm that is pivotable and adjustable in length. For example, the manipulator arm can be telescopic or equipped with a threaded rod or a hydraulic cylinder to advantageously allow stepless length adjustment. The pivot axis of the manipulator arm is advantageously fixed in position.

[0018] Advantageously, the solar cell can be picked up at one end of the manipulator arm. Accordingly, one embodiment provides that the manipulator unit has a manipulator head which can remove individual solar cells from the magazine unit. The manipulator head is advantageously attached to one end of the manipulator arm. For picking up and holding the solar cells, the manipulator head preferably has suction cups to hold the solar cells without damage by means of negative pressure.

[0019] Furthermore, the manipulator head advantageously features a top plate made of a material with high thermal conductivity. The solar cell, which is picked up and held by the manipulator head, preferably rests against this top plate throughout the entire process of connecting it to the flat conductor. This means that the actual soldering process for connecting the flat conductor also takes place while the solar cell is resting on the top plate. The top plate is preferably insulated from the other components of the device and thus decoupled, so that the solar cell itself is not subjected to high currents during the soldering process. Advantageously, the top plate ensures good and rapid heat dissipation from the heat zone to prevent damage to the solar cell due to excessive or prolonged heat exposure. For this purpose, the top plate is advantageously made of a material with high thermal conductivity, such as copper with a thermal conductivity of approximately [value missing in original text].386 W / mK at 20°C.

[0020] The first soldering unit comprises a first plasma source. According to the invention, the plasma jet or plasma arc generated by this serves as a heat source for generating the heat zone in which the flat conductor is melted and connects with the solar cell.

[0021] Furthermore, in one embodiment, the first soldering unit has a hold-down device against which the manipulator head presses the solar cell with its flat conductor to be processed. In the final position for soldering the components, the solar cell with the attached flat conductor is located between the hold-down device and the head plate. Preferably, the head plate, on which the solar cell with the flat conductor rests, is pressed against the hold-down device from below. Advantageously, this pressure is applied with very little force to avoid damaging the components. Tests have shown that a force of approximately 0.3 N is sufficient for this purpose. This pressure ensures that the flat conductor rests on the solar cell with only a minimal solder gap. Preferably, the solder gap is a maximum of 0.2 mm.

[0022] Preferably, the hold-down device is made of an electrically conductive material and also serves as a ground for the soldering process.

[0023] During the actual soldering process, temperatures exceeding 3,000 °C are reached. To prevent damage to the solar cell, it is crucial to keep the heat exposure time as short as possible and ensure the fastest possible heat dissipation from the heated area to cool the solar cell. Heat dissipation occurs via the clamping device and the end plate.

[0024] Accordingly, it is advantageous for the hold-down device to be made of a material with high thermal conductivity. For this purpose, the hold-down device is advantageously made of a material with high thermal conductivity, such as copper with a thermal conductivity of approximately 386 W / mK at 20°C.

[0025] The heat exposure time, i.e., the duration of the soldering process during which the plasma beam acts on the solar cell and the flat conductor to be joined, is between 50 ms and 500 ms, preferably 200 ms. A longer exposure time would damage the solar cell. To avoid this, it is important to keep the exposure time as short as possible and to dissipate the applied heat from the heat zone as quickly as possible, i.e., to cool the material.

[0026] Heat dissipation through the head plate begins as soon as the plasma jet is ignited and continues as long as the solar cell is on the head plate, i.e., until the processed solar cell is placed on the pallet. Heat dissipation at the hold-down clamp also begins as soon as the plasma jet is ignited and continues until the solar cell being processed is pulled back from the hold-down clamp by the manipulator head, i.e., until the contact between the hold-down clamp and the solar cell or flat conductor is broken.

[0027] Because copper, due to its very high thermal conductivity, conducts and absorbs heat very quickly, the heat acts on the solder joint for only milliseconds. This high speed is also the key to success, making the process possible in this form. Tests have shown that if the heat dissipation is insufficient or absent, a hole is immediately burned into the cell.

[0028] Preferably, the clamping device has a recess, at least in the area of ​​the heating zone. For soldering, the solar cell with the flat conductor is held between the clamping device and the end plate. To allow access of the plasma beam to the solar cell with the flat conductor, it is advantageous to provide a recess in the clamping device through which the plasma beam can reach the solar cell. The heating zone is therefore advantageously located within the recess.

[0029] During the actual soldering process, the plasma source generates a plasma arc to create the heat zone, which has a diameter of 2 mm to 4 mm, preferably 2.5 mm. The heat zone is advantageously as small as possible to avoid material damage and to create the most precise solder joint possible, where the flat conductor is connected to the solar cell. However, the heat zone advantageously covers the entire width of the flat conductor. This is approximately 1.5 mm to 2.0 mm wide, so the heat zone is somewhat larger.

[0030] The plasma source preferably comprises a conventional ceramic nozzle in which the plasma jet is generated under a protective gas atmosphere, for example at a tungsten needle, while argon gas flows in to prevent the oxidation of the material to be joined.

[0031] A preferred embodiment provides that at least the area of ​​the plasma arc and the heating zone is free of additional activation or soldering material. The plasma arc or plasma jet is generated under a protective gas atmosphere, but no additional material is introduced into this area that would be deposited on the solar cell during soldering or that would provide the connection to the flat conductor. The protective / argon gas introduced to prevent oxidation is not an electrical contact medium or bonding material.

[0032] After soldering, the processed solar cells are placed on the pallet by the manipulator arm. Advantageously, the device according to the invention provides a conveyor belt on which the pallet for placing the processed solar cells is arranged. After each solar cell is placed, the conveyor belt with the pallet advantageously moves forward by a defined step, i.e., in an output direction. This results in a gap of approximately 1.0 mm to 2 mm between two placed solar cells. Preferably, the gap is approximately 1.5 mm, providing sufficient space to guide the flat conductor of a processed solar cell upwards between this solar cell and the previously processed solar cell.

[0033] Furthermore, it is particularly advantageous if the pallet has several grooves extending longitudinally. Within the scope of the invention, a groove is understood to be a slot or a recess in the pallet, preferably extending over the entire length of the pallet. In one embodiment, the pallet has a central groove extending longitudinally along its center line. When the processed solar cell is placed on the pallet, it is turned over so that the previously upward-facing side, to which the flat conductor is connected, now faces downwards when placed on the pallet, and the flat conductor is positioned in the central groove. Without this central groove, the processed solar cell would not lie flat on the pallet, and the lower flat conductor would create a kind of weak point.

[0034] In another embodiment, the pallet has at least two lateral grooves. Preferably, at least one lateral groove is formed on each side of the central groove. Advantageously, the lateral grooves also extend over the entire length of the pallet. At least the ends of the lateral grooves at the ends of the pallet are open. When the solar cells are placed on the pallet, the vacuum holding the solar cells to the head plate of the manipulator head is released by generating a slight counter-pressure, i.e., a slight airflow. This airflow can be blown out through the lateral grooves; otherwise, the other solar cells on the pallet would be blown away.

[0035] Furthermore, it is advantageous if the pallet is made of a material with high thermal conductivity, such as copper, to ensure good and rapid heat dissipation during the second soldering process. During the second soldering process, the heat from the plasma jet is primarily dissipated via the pallet and the clamping device of the second soldering unit.

[0036] Another embodiment of the device provides that the second functional assembly includes a further soldering unit with a second plasma source for connecting at least two processed solar cells to form a solar cell string. The first functional assembly with the first soldering unit serves to electrically connect the flat conductor to the solar cell. Several such processed solar cells with connected flat conductors can be electrically connected to form a solar cell string in the second functional assembly of the device using the second soldering unit.

[0037] Another advantageous embodiment provides that the second functional assembly has at least one fixing unit to hold the solar cells on the pallet during the second soldering process. The fixing unit is designed separately from the retainer of the second soldering unit, i.e., as an additional component. The retainer of the second soldering unit presses the protruding flat conductor against the solar cell. The fixing unit holds the solar cells firmly on the pallet. Advantageously, the retainer of the second soldering unit is electrically insulated from the other components of the device. Furthermore, the retainer of the second soldering unit also advantageously has a recess, at least in the area of ​​the heating zone.

[0038] Advantageously, two fixing units are provided which press the elongated, rectangular solar cells as evenly as possible against the pallet on both sides, or hold the solar cells in place on the pallet. Furthermore, at least one fixing unit advantageously has at least one spring pin which presses the solar cells against the pallet. In a particularly advantageous embodiment, each fixing unit has two spring pins, which each press or hold a solar cell in place.

[0039] When pressing and holding the solar cells on the pallet, it is important to avoid damage. For this, an even distribution of force and a large contact area are advantageous. The tip or head of the spring pins is preferably spring-loaded to ensure a uniform contact force is applied to the solar cells. The contact force is advantageously well below 1 N, preferably between 0.09 N and 0.32 N.

[0040] For example, the spring-loaded pins can have a soft and flexible tip, such as one made of silicone or plastic. Pressing and holding the solar cells in place prevents the cell being soldered from moving and also prevents the next solar cell from tilting or being partially lifted off the pallet and shifted by the pressure on the conductor tab (the protruding flat conductor). Therefore, it is preferable to press and hold two solar cells at a time: ideally, the cell being soldered and the next one to be soldered.

[0041] The invention also relates to connecting a solar cell to a flat conductor, wherein: - the flat conductor is positioned on the first side of the solar cell, - the solar cell and the flat conductor are pressed together, and - the flat conductor is at least partially melted in a heat zone, whereby - a plasma arc is used as the heat source and at least the heating zone is free of additional material.

[0042] In the first step, the flat conductor is soldered to one side of the solar cell using a plasma arc. This side will be the top of the solar cell, facing the sun. The other side will be the bottom, facing away from the sun. Between the first and second steps, the solar cell is advantageously flipped over when being placed down. In the second step, the processed solar cells are connected to form a solar cell string. The protruding conductor tabs or flat conductors are soldered to the other side of the solar cell, also using a plasma arc. The flat conductor, or more precisely its protrusion, is guided from the first side of one solar cell to the second side of the other.

[0043] In both steps of the invention, a plasma is used as a heat source to connect the flat conductor to the solar cell. The plasma jet is applied to the solder joint under a protective gas atmosphere, meaning that no additional material is deposited there as a contact medium or the like. The electrical connection of the flat conductor to the solar cell or to a transversely running busbar arranged underneath it consists exclusively of the molten material of the conductors.

[0044] Overall, the process is carried out without any additional separating, contact or connecting material, and there are no deposits of additional material in the heating zone.

[0045] A preferred embodiment of the joining method according to the invention comprises at least the following steps: - Ejecting the flat conductor from the feed / cutting unit and positioning the flat conductor below the soldering unit, - Moving the manipulator head from a starting position and picking up a leading solar cell from the magazine unit, - Swiveling the manipulator head with the solar cell in place towards the soldering unit, so that the underside of the solar cell points towards the flat conductor, - Pressing the solar cell against the flat conductor until a predefined solder gap is reached, - Generation of a plasma arc between the first plasma source and the solar cell with the flat conductor, whereby a heat zone is formed in which the flat conductor is at least partially melted and connects with the solar cell, - Separating the flat conductor with an overhang towards the solar cell, - Retraction of the manipulator head with the processed solar cell and the connected flat conductor, - Swiveling the manipulator head with the processed solar cell towards the conveyor belt, - Place the processed solar cell on the pallet so that the underside of the processed solar cell with the connected flat conductor faces downwards and the protrusion of the flat conductor rests on a previously processed solar cell, and - Return of the manipulator head to its starting position.

[0046] The sequence of process steps described here may be advantageous. However, it is within the scope of the invention to vary this sequence as desired.

[0047] First, the flat conductor is dispensed from the feed / cutting unit, for example, unwound from a supply roll, and positioned under the soldering unit so that, in its final state, it extends across the entire width of the solar cell on its upward-facing underside. Advantageously, one end of the flat conductor is as flush as possible with the solar cell, meaning it does not protrude beyond its edge. On the other side of the solar cell, the flat conductor is cut in a later step after the connections are made, leaving a protrusion or conductor tab.

[0048] As a next step, the manipulator head is moved from its starting position and picks up the foremost solar cell from the magazine unit. For example, the solar cell is suctioned in and held against the manipulator head's top plate by means of a vacuum. Holding the solar cell with a vacuum works advantageously on the smooth top surface of the solar cell, so that in the first step, the flat conductor is soldered to the underside of the solar cell. The suction cups would not adhere to the rough underside of the solar cell, and a vacuum could not be generated there.

[0049] The solar cells used conventionally have a transverse collector conductor made of a silver alloy running along their top surface. This conductor collects the voltage generated by the much thinner conductors that run lengthwise along the solar cell. The flat conductor to be connected or soldered is first connected to the underside of the solar cell. In the second step, the protruding section of the flat conductor on the top surface of the solar cell is connected lengthwise to the transverse collector conductor.

[0050] For the purposes of this patent application, the top or sun-facing side of the solar cell is understood to be the side facing (solar) radiation, which represents the negative terminal and on which the conductors are arranged. The back or bottom side of the solar cell represents the positive terminal.

[0051] Once the flat conductor is positioned under the soldering unit and the solar cell has been removed from the magazine unit, the manipulator head, with the solar cell in place, pivots towards the soldering unit and approaches it, or rather the soldering unit's clamp, until the top of the solar cell is pressed against the flat conductor, leaving a predefined solder gap. The flat conductor is located on the upward-facing underside of the solar cell, beneath the soldering unit. The solar cell lies flat and flush against the head plate. Advantageously, the clamp has a recess so that the area of ​​the heating zone under the ceramic nozzle of the soldering unit remains uncovered.

[0052] During the actual soldering process, a plasma jet or arc is generated between the plasma source and the solar cell with the flat conductor. The flat conductor and the clamping device serve as the negative terminal or ground, and the tungsten needle of the soldering unit as the positive terminal. The current flow during soldering is therefore from the tungsten needle, through the flat conductor, to the clamping device. The plasma jet is ignited by means of a high frequency with a current of 2 A to 20 A. The distance between the tungsten needle and the solar cell or the flat conductor is between 0.2 mm and 0.6 mm. Argon is conventionally used as the shielding gas. According to the invention, it is not necessary to deposit any additional contact material onto the solar cell for connection to the flat conductor during the soldering process.

[0053] The plasma jet acts as a heat source, striking the solar cell in the area of ​​the flat conductor and forming a heated zone. Here, the flat conductor is at least partially melted and fuses with the solar cell. The heat exposure time is between 50 ms and 500 ms, preferably 200 ms. The heated zone has a diameter of approximately 2 mm to 4 mm, preferably 2.5 mm, and is thus slightly wider than the flat conductor, which is approximately 1.5 mm to 2.0 mm thick. Crucially, in carrying out the inventive process with a plasma jet as the heat source, the very high temperatures of the plasma act on the material for only an extremely short time, and the heat present in the material is dissipated very quickly. This is achieved through the short heat exposure time and the efficient heat dissipation via the hold-down device and the end plate, or, in a second step, via the hold-down device and the pallet.

[0054] The heat applied to the solar cell or flat conductor by the plasma jet is dissipated via both the clamping device and the end plate. Ideally, these components are made of a material like copper with high thermal conductivity. The clamping device allows heat to be dissipated as long as it maintains contact with the solar cell. The end plate allows heat to be dissipated until the processed solar cell is placed on the conveyor belt.

[0055] Once the soldering process is complete, the rear end of the flat conductor is cut off using the feed / cutting unit. Preferably, the flat conductor is not cut flush at the rear end, but with an overhang or tab that extends beyond the edge of the solar cell. This overhang can be connected to another processed solar cell in a later step. Advantageously, the length of the overhang is between 1 / 2 and 2 / 3 of the width of the solar cell.

[0056] The manipulator head then retracts or moves downwards a short distance, thus breaking contact between the head plate and the hold-down device.

[0057] To place the processed solar cell on the conveyor belt, the manipulator head swivels around and places the processed solar cell, with its underside facing upwards, onto the pallet on the conveyor belt. During placement, the solar cell is rotated and lies upside down on the pallet. The top side of the solar cell without the flat conductor faces upwards, while the underside with the attached flat conductor faces downwards. The protruding flat conductor then rests on a previously processed solar cell. This means that the flat conductor is guided between two adjacent solar cells and upwards.

[0058] In a further step, the manipulator head returns to its starting position.

[0059] After a processed solar cell is placed on the pallet, the conveyor belt moves a defined distance in an exit direction to make room for the next processed solar cell. The conveyor belt advances in defined increments, ensuring a gap between each solar cell. This gap is advantageously approximately 1.0 mm to 2.0 mm, allowing the protruding flat conductor between the two cells to pass through. The exit direction is advantageously aligned with the direction to the next soldering unit for further processing of the solar cells.

[0060] The steps described above can be repeated as often as desired.

[0061] As a further step, two processed solar cells placed side by side on the conveyor belt can advantageously be connected together. The protruding flat conductors are connected to the solar cells. Preferably, the protruding flat conductors of the rear solar cells (i.e., viewed in the direction of origin) are guided from bottom to top onto the front solar cell and soldered there.

[0062] For soldering, the clamp of the next soldering unit presses the protruding flat conductor of the solar cell to be processed onto the top surface of the solar cell being processed next. This ensures a solder gap of no more than 0.2 mm. Furthermore, the contact between the solar cell and the clamp allows for effective heat dissipation.

[0063] Secondly, during the second soldering process, the spring pins of the fixing units press the solar cell being processed, as well as the next solar cell to be processed, against the pallet. Pressing the protruding conductor tab onto the front solar cell creates the risk of the rear solar cell being lifted and displaced. This can be prevented by pressing down the next solar cell as well.

[0064] According to the invention, during the second soldering process, a heat zone is also generated on the top side of the solar cell being processed using the second plasma source. In this zone, the protruding flat conductor of the next solar cell to be processed is at least partially melted and bonds with the solar cell. The exposure time is kept as short as possible during the second soldering process as well. Rapid heat dissipation is ensured via the clamping device and the pallet, so that the thermal stress and the risk of damage to the solar cell are kept to a minimum during the second soldering process. The second soldering process is also carried out under a protective gas atmosphere and free from any deposits of additional contact or bonding material.

[0065] The method according to the invention can preferably be carried out with a preceding apparatus according to the invention. The described sequence of the method steps is preferred and advantageous, but is not to be understood as restrictive. It is also within the scope of the invention to vary the sequence of individual steps. Furthermore, it is advantageous that the method steps for the first and second soldering processes can also be carried out at least partially simultaneously with the apparatus according to the invention.

[0066] The invention is described in more detail below using an exemplary embodiment and the figures, whereby only the features essential for understanding are shown.

[0067] They show in detail: Fig. 1: a section of the second functional assembly of the device according to the invention in the area of ​​the second soldering unit in a first position, Fig. 2: the section from the second functional assembly of the device according to the invention in the area of ​​the second soldering unit in a second position, and Fig. 3: the section of the second functional assembly of the device according to the invention in the area of ​​the second soldering unit in a cross-section in the second position.

[0068] The Fig. 1, Fig. 2 to Fig. Figures 3 each show a section of the second functional assembly of the device according to the invention in the area of ​​the second soldering unit 1 in different positions or process steps.

[0069] The soldering unit 1 comprises a conventional ceramic nozzle 2 with a tungsten needle for generating a plasma jet. Furthermore, the soldering unit 1 includes a clamp 3, which presses the flat conductors or their protrusions 7 against the solar cells 6 to be processed during the second soldering process, especially in the area of ​​the heat zone. The solar cells 6 are placed on a pallet 4 on a conveyor belt 5. In the process steps of the second soldering process shown here as an example, the solar cells 6 have already been processed to the extent that, in the first soldering process, the flat conductors 7 were connected to the undersides of the solar cells 6 and then placed on the pallet 4 with their still unprocessed top side facing upwards. After each solar cell 6 is placed, the conveyor belt 5 moves with the pallet 4 in an outward direction, here to the right, until there is a gap of approximately 1 mm to 2 mm between two successively placed solar cells 6.The protrusion 7 of the flat conductor of the last placed solar cell 6b lies on the top side of the previously placed solar cell 6a. The distance between the solar cells 6a and 6b is large enough that the protrusion of the flat conductor 7 of the last placed solar cell 6b can be guided from bottom to top onto the previously placed solar cell 6a without kinking.

[0070] The pallet 4 has several grooves. A central groove 4a is formed along the center line of the pallet 4. The flat conductor on the underside of the placed solar cells 6 is positioned in this central groove 4a, allowing the solar cell 6 to lie flat and level on the pallet 4. Furthermore, several longitudinal lateral grooves 4b are formed on both sides of the central groove 4a, open to the sides of the pallet 4 and to the front and rear. When the solar cells 6 are placed on the pallet 4 and the vacuum holding them against the head plate of the manipulator arm (not shown in this section) is released, a brief counter-pressure or puff of air is generated, which can escape through the lateral grooves 4b. Otherwise, the already placed solar cells 6 would be blown away and their exact position altered.

[0071] Two fixing units 8 are attached to the hold-down device 3. The fixing units 8 are moved up and down with the hold-down device 3. The hold-down device 3 presses the protrusion 7 of the flat conductor in the area around the heating zone against the solar cell 6. The fixing units 8 each press one solar cell 6a, which is currently being processed, and the next solar cell 6b to be processed, whose flat conductor protrusion 7 is to be connected to the front solar cell 6a, against the pallet 4, thus preventing the next solar cell 6b from moving due to the pressure on the flat conductor protrusion 7. In order to exert the most uniform pressure possible on the solar cells 6a and 6b and to avoid damage, the fixing units 8 each have two spring pins 9 with a rounded and flexible tip.The fixing units 8 themselves are made of a non-conductive material such as plastic to prevent current flow into the solar cells 6 and other components of the device.

[0072] The Fig. Figure 1 shows the soldering unit 1 with the ceramic nozzle 2, the hold-down device 3 and the fixing units 8 in a first or starting position for the soldering process, i.e. before the hold-down device 3 with the fixing units 8 is lowered towards the solar cells 6.

[0073] The Fig. Figure 2 shows the soldering unit 1 with the ceramic nozzle 2, the hold-down device 3 and the fixing units 8 in a second position, i.e. during the soldering process, whereby the hold-down device 3 with the fixing units 8 has already been lowered to hold the solar cells 6a, 6b and the flat conductor protrusion 7.

[0074] The Fig. Figure 3 shows the section of the Fig. 1 and Fig.2 in a cross-section. In this cutaway view, it is clearly visible that the hold-down device 3 has a recess in the area of ​​the plasma jet's heat zone under the ceramic nozzle 2. The tungsten needle of the soldering unit 1 is also visible. Both soldering processes take place under a protective gas atmosphere, and no additional material is deposited to connect the flat conductor to the solar cells.

[0075] Although the invention has been illustrated and described in detail by the preferred embodiment, the invention is not limited by the disclosed examples, and other variations can be derived by a person skilled in the art without departing from the scope of the claims. In particular, the invention is not limited to the specified combinations of features, but other combinations and partial combinations of the disclosed features that are obviously feasible to a person skilled in the art can also be formed. Thus, embodiments that are not explicitly shown or explained in the figures, but which can be derived and generated by separate combinations of features from the explained embodiments, are also to be considered as encompassed and disclosed by the invention. Likewise, it is also within the scope of the invention to effect a mechanical reversal of the functions of the individual mechanical elements of the invention. Reference symbol list 1 soldering unit 2 ceramic nozzles 3 hold-down devices 4 pallets 4a Center groove 4b lateral grooves 5 Conveyor belt 6 solar cells 6a front solar cell processed in the respective step 6b rear solar cell to be processed next 7. Flat conductor overhang 8 Fixing unit 9 spring pen QUOTES INCLUDED IN THE DESCRIPTION

[0000] This list of documents cited by the applicant was automatically generated and is included solely for the reader's convenience. The list is not part of the German patent or utility model application. The DPMA accepts no liability for any errors or omissions. Cited patent literature

[0000] WO 2014 / 033047 A1

[0003] DE 10 2010 013 850 A1

[0003]

Claims

[1] Device for electrically connecting solar cells (6), wherein a first functional assembly connects a flat conductor to a solar cell (6) and a second functional assembly connects several solar cells (6) to form a solar cell string, wherein the first functional assembly comprises at least: 1.

1. a feed / cutting unit for the flat conductor, 1.

2. a magazine unit for storing the solar cells (6), 1.

3. a manipulator unit for positioning a solar cell relative to the flat conductor, 1.

4. a first soldering unit with a first plasma source for generating a heat zone in which the flat conductor is at least partially melted and bonds with the solar cell, and 1.

5. a pallet (4) for placing the processed solar cells. [2] Device according to the preceding claim 1, characterized bythat the manipulator unit has a manipulator arm which is swivelling and adjustable in length. [3] Device according to the preceding claim 2, characterized by , that the manipulator unit has a manipulator head which can remove individual solar cells (6) from the magazine unit. [4] Device according to the preceding claim 3, characterized by that the manipulator head has a head plate made of a material with high thermal conductivity. [5] Device according to any one of the preceding claims 1 to 4, characterized by , that the soldering unit has a hold-down device against which the manipulator head presses the solar cell (6) to be processed with the flat conductor. [6] Device according to the preceding claim 5, characterized by that the hold-down device is made of a material with high thermal conductivity. [7] Device according to any one of the preceding claims 1 to 6, characterized by that the plasma source forms a plasma arc to generate the heat zone, wherein the heat zone has a diameter of 2 mm to 4 mm, preferably 2.5 mm. [8] Device according to any one of the preceding claims 1 to 7, characterized by , that at least the area of ​​the plasma arc and the heating zone is free of additional activation or solder material. [9] Device according to any one of the preceding claims 1 to 8, characterized by , that a conveyor belt (5) is provided on which the pallet (4) is arranged for placing the processed solar cells (6). [10] Device according to any one of the preceding claims 1 to 9, characterized by , that the pallet (4) has several grooves (4a, 4b) running in its longitudinal direction. [11] Device according to any one of the preceding claims 1 to 10, characterized by, that the second functional assembly has a further soldering unit (1) with a second plasma source for connecting at least two processed solar cells (6a, 6b) to form a solar cell string. [12] Device according to any one of the preceding claims 1 to 11, characterized by , that the second functional assembly has at least one fixing unit (8) to hold the solar cells (6a, 6b) on the pallet (4) during the second soldering process. [13] Device according to the preceding claim 12, characterized by , that the at least one fixing unit (8) has at least one spring pin (9) which presses the solar cells (6a, 6b) against the pallet (4). [14] Connecting a solar cell (6) to a flat conductor, wherein: 14.

1. the flat conductor is positioned on one side of the solar cell (6), 14.

2. the solar cell (6) and the flat conductor are pressed together, and 14.

3. the flat conductor is at least partially melted in a heat zone, whereby 14.

4. a plasma arc is used as the heat source and at least the heating zone is free of additional material.

Images