This invention relates to the field of printheads for producing at least one gridline, in particular a plurality of parallel gridlines, on an upper surface of a target substrate, in particular for producing a pattern for a solar cell structure.

The basic principle of the process of screen printing is the use of a mesh screen to reproduce the same image over and over again. The way that screen printing is used in the process of making solar cells is that PV solar cells are often metalized through a screen-printing process. This is the application of different types of metallization pastes onto e.g. a c-Si cell. Thereby, the paste is applied to a mesh screen and pushed through with a squeegee to transfer the paste on the open image area to the desired substrate. This process can be repeated as many times as the screen materials will last.

According to the state of the art, printheads for squeezing the paste are configured and adapted to work in one direction only. In a first step according to the methods known in the state of the art the mesh screen is flooded with the paste and then the squeegee is moved into a first direction over the mesh screen and the paste to transfer the same on the substrate. As the width of the squeegee is not necessarily the width of the substrate, , the squeegee is lifted up, moved back in the lifted position in the opposite direction to the initial starting point of its movement, , and then the process is repeated.

The disadvantages of the printheads for screen printing according to the state of the art are that the printing process is time consuming as the printhead is moved back without printing and the paste itself is not used efficiently by flooding the paste over the mesh screen while not all of the paste may be used.

The object of the present invention is therefore to fasten the printing of gridlines on a target substrate and to provide a minimized paste loss and an efficient paste transfer to the substrate.

This object is solved by a printhead for producing at least one gridline, in particular a plurality of parallel gridlines, on an upper surface of a target substrate, in particular for producing a pattern for a solar cell structure, by screen or stencil printing having at least one inlet port, at least one dispensing orifice, and one or more flow channels communicating between said at least one inlet port and said at least one dispensing orifice, further comprising at least two printing plates which are placed in independently definable angles relative to the upper surface of the target substrate, wherein the at least two printing plates are independently moveable between a printing position and a stop position, and wherein at least a first printing plate and at least a second printing plate are arranged at opposite sites of said at least one dispensing orifice, and wherein in the printing position the printing plates are arranged closer to the upper surface of a target substrate than in the stop position.

The word "exemplary" is used herein to mean "serving as an example, instance, or illustration." Any implementation described herein as "exemplary" is not necessarily to be construed as preferred or advantageous over other implementations.

The printhead according to the present disclosure may be used for producing fine lines on a substrate which is based on multi-crystalline silicon wafers whereby the fine line produced is according to a solar cell structure. The fine lines are defined as fingers. Screen or stencil printing applied in order to produce the fine line (fingers). The printhead may comprise an inlet port which can have single or multiple channels which may be used to connect tubing supplying solar cell paste whereby solar paste will be supplied continuously.

The printhead may comprise a material feed mechanism whereby the inlet port on the printhead will be connected with paste supplying tubing and the paste will be forced via a force to fill up the space in between the plate and the screen or stencil.

The printhead may comprise a transport mechanism and material feed system. The material may be forced through a channel to the dispensing orifice in front of the blades. Transport mechanism will move the printhead to the specified gap between the stencil/screen and wafer surface. The blades with specified angle will move forward as per position defined and stop as per position defined.

With a printhead according to the present disclosure it is possible to print with forward direction (Cycle 1) and backward (Cycle 2) direction e.g. for front side solar cells metallization. Dependent of the printing direction one of the two printing plates is moved into the printing position, while the second printing plate is in or moved to the stop position. Each blade has independent movement and the up-down movement of each individual blades. Preferably, said two printing plates are arranged opposite to each other in mirrored angles relative to the upper surface of the substrate. The, in case, single squeegee holder provides thereby the paste trough the at least one orifice according to process requirements and setup. The triggering for the up-down movement is based on the sensor triggering on the position of printing.

The movement of the printing blades to achieve the desired printing angle and/or to move the printing blades into the stop or printing position is achieved via movement actuated pneumatically, hydraulically and/or by at least one electric motor.

The possible printing mode provided by the printhead according to the present disclosure does not require any flooding mechanism and enables printing of solar cells opposite movement direction. Thereby, the printhead dispenses the paste directly next to the printing blades during the printing cycles continuously.

Finally, the print head according to the present disclosure enables printing of solar cells in lesser cycle time as printing is possible backward and forward directions of the movement of the printhead.

According to one example of the present disclosure, the printhead may comprise at least one controller, wherein said controller is configured and adapted to determine the movement direction of the printhead, and wherein the movement of the printing plates from the printing position to the stop position and reverse is controlled by the controller based on the detected printing position.

By use of such a controller the printing and stop position of each of the printing plates can be configured automatically depending on the movement direction of the printhead.

Thereby, it may be of advantage according to one embodiment that in case the at least one first printing plate is moved to or in the printing position, the second printing plate is moved to or in the stop position and reciprocally, and wherein the movement between the printing position and the stop position of the printing plates is actuated pneumatically, hydraulically and/or by at least one electric motor which is triggered by the printing position which is triggered by the controller.

This may in particular be of advantage as only one blade of the printing head is in contact with the screen or stencil at any time to transfer the paste to the substrate.

According to one example it may be preferred that a material feed mechanism for supplying said extrusion material, preferably in form of a paste, to said inlet port of the printhead such that said extrusion material is selectively forced through said at least one flow channel and exits through said at least one dispensing orifice. By the efficient paste transfer next to the printing plates fine line printing is possible. Stabile paste composition are provided due to paste rolls at anytime due to the movement of the dual blades.

According to a further example of the present disclosure, the printing blades are arranged in an adjustable angle a in a range of 30° to 70°, in particular in a range of 45° to 60°, relative to the upper surface of the target substrate, wherein the printing blades have preferably a thickness in a range of 0.05 to 0.5 mm, in particular in a range of 0.1 to 0.3 mm, and wherein preferably at least one of the printing blades comprise or consist of stainless steel.

Such angles of the printing plates have shown to be advantageously.

Moreover, according to one example of the present disclosure, at least one side wiper is arranged at or adjacent to at least one of the printing blades, in particular each printing blade comprises at least one side wiper, preferably two side wipers arranged at opposite sides of each of the printing blade, wherein the at least one side wiper is configured and adapted to create a limited area for the movement and circulation of the extrusion material, preferably in form of a paste, and in particular also providing effective roll of the said extrusion material at both printing directions and also minimizing harden extrusion material on the substrate surface area.

The side wipers according to the present disclosure allow to dispense the paste in a restricted area. Thereby, the paste losses are significantly reduced via a reduction of the paste being exposed to unprinted areas. Instead, the paste is dispensed directly next to first or second printing plate. The side wipers may be configured and arranged in order to create minimum area for the solar cell paste movement and circulation and also providing effective roll of the solar cell paste at both printing directions in order to ensure effective solar paste transfer from the stencil or screen to wafer surface. The said side wipers may be made of rubber or polyurethane material and supported by steel frames.

Furthermore, according to one example of the present disclosure a transport mechanism is provided for supporting the printhead and/or said target substrate, and for moving the printhead relative to said target substrate such that extrusion material , preferably in form of a paste, exiting said at least one dispensing orifice forms said at least one gridline on the upper surface of the target substrate.

According to a further example of the present disclosure a printhead may further comprise means for controlling said material feed mechanism and said transport mechanism such that during a first time period, a material feed mechanism forces an extrusion material, preferably in form of a paste, through said at least one dispensing orifice while a transport mechanism moves said printhead over said target substrate in a first direction such that first structures are formed on said target substrate starting from or adjacent to a first side edge of said target substrate, wherein at least the first printing blade is in the printing position and at least the second printing blade is in the stop position, and during a second time period, said material feed mechanism forces said extrusion material through said at least one dispensing orifice while said transport mechanism moves said printhead over said target substrate in a second direction opposite to the first direction such that first and/or second structures are formed on said target substrate, wherein at least the second printing blade is in the printing position and at least the first printing blade is in the stop position.

Finally, the according to one example the printhead may comprise an connection to the integrated software of a printing machine which indicates the present printing mode, wherein the software is capable of triggering the first and second blade to start the movement according to the position and perform the function continuously.

Furthermore, the present invention provides a use of a printhead according to the present disclosure for producing or within production of a solar cell.

Moreover, the present disclosure provides a method for producing at least one gridline, in particular a plurality of parallel gridlines, on an upper surface of a target substrate, in particular for producing a pattern solar cell structure, by screen or stencil printing using a printhead according the disclosure, wherein the method comprises during a first time period, causing a material feed mechanism to force a gridline material through the at least one dispensing orifice while causing a transport mechanism to move said printhead relative to said target substrate such that first structures are formed on said target substrate starting from or adjacent to a first side edge of said target substrate in a first direction, wherein the first printing blade is in the printing position and the second printing blade is in the stop position; and during a second time period following the first time period, causing said material feed system to force said gridline material through said at least one dispensing orifice while causing said transport mechanism to move said printhead relative to said target substrate i a second direction opposite to the first direction such that first and/or second structures are formed on said target substrate, wherein the second printing blade is in the printing position and the first printing blade is in the stop position.

The foregoing aspects and many of the attendant advantages of this invention will become more readily appreciated as the same become better understood by reference to the following detailed description, when taken in conjunction with the accompanying drawing, wherein: FIG. 1 is a schematic side view of an example of the printhead according to an embodiment; and

FIG. 2 is is a schematic side view of the printhead shown in figure 1 in the back printing cycle.

The various embodiments will be described in detail with reference to the accompanying drawings. Wherever possible, the same reference numbers will be used throughout the drawings to refer to the same or like parts. References made to particular examples and implementations are for illustrative purposes, and are not intended to limit the scope of the invention or the claims.

While illustrative examples are illustrated and described below, it will be appreciated that various changes can be made therein without departing from the spirit and scope of the disclosure. In that regard, the detailed description set forth below, in connection with the appended drawings is intended only as a description of various examples of the disclosed subject matter and is not intended to represent the only examples. Each example described in this disclosure is provided merely as an example or illustration and should not be construed as preferred or advantageous over other examples. The illustrative examples provided herein are not intended to be exhaustive or to limit the disclosure to the precise forms disclosed. Similarly, any steps described herein may be interchangeable with other steps, or combinations of steps, in order to achieve the same or substantially similar result.

Figure 1 shows a schematic side view of an example of the printhead according to an example of the present disclosure. The printhead 1 is a printhead for producing at least one gridline of a pattern for a solar cell structure by screen or stencil printing. The printhead 1 has one inlet port (not shown), a squeegee holder 3, at least one dispensing orifice 5, and one flow channel 7

communicating between said inlet port 3 and said dispensing orifice 5.

Two printing plates 9, 11, which are placed in independently definable angles a relative to the upper surface of the target substrate, are independently moveable between a printing position and a stop position. In figure 1 it is shown that a first printing plate 9 is in the printing position while the second printing plate 11 is in the stop position. This allows a printing in the first direction A of the paste through a mesh 13 onto the target substrate 15.

With a printhead according to figure 1 it is possible to print with forward direction A and in backward B direction (shown in figure 2). Dependent of the printing direction one of the two printing plates 9, 11 is moved into the printing position, while the second printing plate is in or moved to the stop position. Said two printing plates 9, 11 are arranged opposite to each other in mirrored angles relative to the upper surface of the substrate. The squeegee holder 3 provides thereby the paste trough the at least one orifice 5 according to process requirements and setup. The triggering for the up-down movement is based on the sensor triggering (not shown) on the position of printing. In case of printing in direction B, the second printing plate 11 is in the printing position and the first printing plate 9 is in the stop position. As can be derived from figures 1 and 2 easily, the printhead 1 is able to provide the paste in any printing direction with the same quality.Therefore, the print head 1 according to the present disclosure enables printing of solar cells in lesser cycle time as printing is possible backward and forward directions of the movement of the printhead.

The movement between the printing position and the stop position of the printing plates 9, 11 is actuated pneumatically by pneumatic cylinders 17, 19 in the examples shown. Of course, other types of actuation of the printing plates 9,11 is possible and the pneumatic cylinders shown are just one possible type of realization.

Not shown in figures 1 and 2 are the side wipers, which are arranged at or adjacent to at least one of the printing blades 9,11 which are configured and adapted to create a limited area for the movement and circulation of the paste also provide effective roll of the said extrusion material at both printing directions. The side wipers according allow to dispense the paste in a restricted area.

Furthermore, the transport mechanism of the present disclosure for supporting the printhead and/or said target substrate, and for moving the printhead relative to said target substrate is not shown in figures 1 and 2.

It is thereby obvious for those skilled in the art that several transport mechanisms are suitable for fulfilling the requirements of screen or stencil printing with a printhead 1 according to the present disclosure.

The features of the present invention disclosed in the description above and in the claims can be used for implementing the invention in its different embodiments both individually and in every possible combination thereof. The preceding description of the disclosed embodiments is provided to enable any person skilled in the art to make or use the present invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the generic principles defined herein may be applied to other embodiments without departing from the spirit or scope of the invention. Thus, the present invention is not intended to be limited to the embodiments shown herein but is to be accorded the widest scope consistent with the following claims and the principles and novel features disclosed herein. PAGE BLANK UPON FILING