Patent Publication Number: US-2011065227-A1

Title: Common laser module for a photovoltaic production line

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     Embodiments of the present invention generally relate to a production line for the fabrication of thin film photovoltaic modules. In particular, embodiments of the present invention relate to an automated production line using a common module of laser scribe tools for providing consistent scribe lines in multiple layers in the formation of thin film photovoltaic modules. 
     2. Description of the Related Art 
     Photovoltaic (PV) cells or solar cells are devices that convert sunlight into direct current (DC) electrical power. Typical thin film solar cells have a PV layer comprising one or more p-i-n junctions. Each p-i-n junction comprises a p-type layer, an intrinsic type layer, and an n-type layer. When the p-i-n junction of the solar cell is exposed to sunlight (consisting of energy from photons), the sunlight is converted to electricity through the PV effect. 
     Thin film solar cells are typically formed in series on a large area substrate to form a solar module. The solar modules are formed by scribing trenches in the various thin film layers deposited on the large area substrate during the fabrication process to both isolate and electrically connect the solar cells in series. In order to maintain consistency and throughput, state of the art solar module production lines use different laser modules at various locations in the production line. This is in part due to the use of particular wavelength lasers used for scribing trenches through different film layers in the formation of the solar cell modules. As a result, state of the art solar cell production lines have lengthy, inflexible process routes that consume a considerable amount of costly fabrication facility space and have a higher production line cost-of-ownership due to the requirement to house multiple different spare parts. 
     Therefore, there is a need for a process and system for fabricating solar modules incorporating a common module of laser scribe tools to decrease cost and facility space requirements, while improving the various scribing processes, system flexibility, and overall system throughput. 
     SUMMARY OF THE INVENTION 
     In one embodiment of the present invention, a laser scribe module for scribing a series of trenches in multiple material layers, including at least a front contact layer, a photovoltaic layer, and a back contact layer, deposited on a substrate, comprises an automation device configured to receive and transport the substrate within the module, one or more reading devices configured to scan a unique reference designator assigned to the substrate, a plurality of laser scribing tools, each configured to emit radiation at substantially the same wavelength, and a system controller configured to receive information from the one or more reading devices, identify the material layer needing to be scribed, send commands to the automation device to transport the substrate to one of the plurality of laser scribing tools, and configure parameters of the laser scribing tool for scribing the identified material layer. 
     In another embodiment, a process for scribing lines in multiple layers of a solar cell device comprises receiving a substrate having one or more material layers disposed thereon into a laser scribe module, wherein the laser scribe has a plurality of laser scribe tools disposed therein, each laser scribe tool configured to emit radiation at substantially the same wavelength, transferring the substrate to an available laser scribe tool via an automation device and a system controller, setting parameters of the available laser scribe tool based on a top material layer disposed on the substrate via the system controller, wherein the top material layer is selected from the list consisting of a front contact layer, a photovoltaic layer, and a back contact layer, and scribing a series of lines into the top material layer via the available laser scribe tool and the system controller. 
     In another embodiment, a system for fabricating solar cell modules comprises a loading module configured to receive a substrate having a front contact layer disposed thereon, a first processing module configured to receive the substrate having the front contact layer disposed thereon with a series of trenches scribed through the front contact layer and deposit a photovoltaic layer over the scribed front contact layer, a second processing module configured to receive the substrate having the photovoltaic layer disposed thereon with a series of trenches scribed through the photovoltaic layer and deposit a back contact layer over the scribed photovoltaic layer, a common laser module having a plurality of laser tools for scribing the series of lines in each layer deposited on the substrate, wherein each laser tool is configured to emit radiation at substantially the same wavelength, and a system controller configured to set and control parameters of each of the laser tools based on the top layer deposited on the substrate needing to be scribed. 
     In yet another embodiment of the present invention, a process for fabricating solar cell modules comprises receiving a substrate having a transparent conducting oxide layer deposited thereon into a common laser module having a plurality of laser scribing tools, wherein each laser scribing tool is configured to emit radiation at substantially the same wavelength, transferring the substrate to a first available laser scribing tool via an automation device and a system controller, setting at least a laser pulse frequency of the first available laser scribing tool via the system controller, scribing a series of trenches through the transparent conducting oxide layer, transferring the substrate into a first processing module having at least one cluster tool with at least one chamber via the automation device, depositing one or more photovoltaic layers over the scribed transparent conducting oxide layer, transferring the substrate having the one or more photovoltaic layers disposed thereon to a second available laser scribing tool within the common laser module via the automation device, setting at least a laser pulse frequency of the second available laser scribing tool via the system controller, scribing a series of trenches through the one or more photovoltaic layers, transferring the substrate into a second processing module having at least one deposition chamber, depositing a back contact layer over the scribed photovoltaic layers, transferring the substrate having the back contact layer deposited thereon to a third available laser scribing tool within the common laser module via the automation device, setting at least a laser pulse frequency of the third available laser scribing tool via the system controller, and scribing a series of trenches through the back contact layer. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       So that the manner in which the above recited features of the present invention can be understood in detail, a more particular description of the invention, briefly summarized above, may be had by reference to embodiments, some of which are illustrated in the appended drawings. It is to be noted, however, that the appended drawings illustrate only typical embodiments of this invention and are therefore not to be considered limiting of its scope, for the invention may admit to other equally effective embodiments. 
         FIG. 1  is a simplified, schematic flow chart illustrating one embodiment of a process sequence including a plurality of processes used to form a solar module using a solar module production line. 
         FIG. 2  is a simplified, schematic plan view of one embodiment of the solar cell module production line illustrating process modules for use with the process sequence of  FIG. 1 . 
         FIG. 3  is a schematic plan view of a solar module having a plurality of solar cells formed on a substrate. 
         FIG. 4  is a schematic, cross-sectional view of a portion of the solar module along section line  4 - 4  shown in  FIG. 3 . 
         FIG. 5  is a schematic plan view of the common laser module according to one embodiment of the present invention. 
         FIG. 6A  is a schematic plan view of a laser scribe tool according to the present invention. 
         FIG. 6B  is a schematic, cross-sectional view of the laser scribe tool in  FIG. 6A . 
         FIG. 6C  is a schematic depiction of a laser device described herein. 
         FIG. 6D  is a schematic, cross-sectional view of an optical fiber from the laser device in  FIG. 6C . 
     
    
    
     For clarity, identical reference numerals have been used, where applicable, to designate identical elements that are common between figures. It is contemplated that features of one embodiment may be incorporated in other embodiments without further clarification. 
     DETAILED DESCRIPTION 
     Embodiments of the present invention generally relate to an automated production line using a common laser scribe module for providing consistent scribe lines in multiple layers during the formation of thin film photovoltaic modules. The common laser scribe module includes a plurality of identical, programmable laser tools configured to emit radiation at a common wavelength. Substrates flowing through the production line are tracked by a system controller, which identifies available laser tools within the common laser scribe module and routes substrates to available tools for scribing features in one or more layers disposed on the substrates. The system controller also sets and controls laser parameters, such as power, pulse frequency, pulse width, and laser pattern, in order to accurately and consistently produce scribed lines in the appropriate material layer of the substrate. 
       FIG. 1  is a simplified, schematic flow chart illustrating one embodiment of a process sequence  100  including a plurality of processes used to form a solar module  300  using a solar module production line  200 .  FIG. 2  is a simplified, schematic plan view of one embodiment of the production line  200  illustrating process modules and other aspects of the system design. 
     In general, a system controller  290  may be used to control one or more components found in the production line  200 . The system controller  290  generally facilitates the control and automation of the overall production line  200  and typically includes a central processing unit (CPU) (not shown), memory (not shown), and support circuits (or I/O) (not shown). The CPU may be one of any form of computer processors that are used in industrial settings for controlling various system functions, substrate movement, chamber processes, and support hardware (e.g., sensors, robots, motors, lamps, etc.), and monitor the processes (e.g., substrate support temperature, power supply variables, chamber process time, I/O signals, etc.). The memory is connected to the CPU, and may be one or more of a readily available memory, such as random access memory (RAM), read only memory (ROM), floppy disk, hard disk, or any other form of digital storage, local or remote. Software instructions and data can be coded and stored within the memory for instructing the CPU. The support circuits are also connected to the CPU for supporting the processor in a conventional manner. The support circuits may include cache, power supplies, clock circuits, input/output circuitry, subsystems, and the like. A program (or computer instructions) readable by the system controller  290  determines which tasks are performable on a substrate. Preferably, the program is software readable by the system controller  290  that includes code to perform tasks relating to monitoring, execution and control of the movement, support, and/or positioning of a substrate along with the various process recipe tasks and various chamber process recipe steps being performed in the production line  200 . In one embodiment, the system controller  290  also contains a plurality of programmable logic controllers (PLC&#39;s) that are used to locally control one or more modules in the solar cell production, and a material handling system controller (e.g., PLC or standard computer) that deals with the higher level strategic movement, scheduling and running of the complete production line  200 . 
       FIG. 3  is a schematic plan view of a solar module  300  having a plurality of solar cells  312  formed on a substrate  302 . The plurality of solar cells  312  are electrically connected in series and are electrically connected to side busses  314  located at opposing ends of the solar module  300 . A cross-buss  316  is electrically connected to each of the side busses  314  to collect the current and voltage generated by the solar cells  312 . A junction box  308  acts as an interface between leads (not shown) from the cross-busses  316  and external electrical components that will connect to the solar module  300 , such as other solar modules or a power grid. 
     In order to form a desired number and pattern of solar cells  312  on the substrate  302 , a plurality of scribing processes may be performed on material layers formed on the substrate  302  to achieve cell-to-cell and cell-to edge isolation.  FIG. 4  is a schematic cross-sectional view of a portion of the solar module  300  along section line  4 - 4  shown in  FIG. 3 . As shown, the solar module  300  includes the substrate  302 , such as a glass substrate, polymer substrate, metal substrate, or other suitable substrate, having a front surface  305  with thin films formed over the substrate  302  on a back surface  306  opposite the front surface  305  of the substrate  302 . In one embodiment, the substrate  302  is a glass substrate that is about 2200 mm×2600 mm×3 mm in size. The solar module  300  further includes a front contact layer  310  formed over back surface  306  of the substrate  302 . The front contact layer  310  may be any optically transparent and electrically conductive film, such as a transparent conducting oxide (TCO), formed to serve as a front contact electrode for the solar cells  312 . Examples of TCO include zinc oxide (ZnO), aluminum zinc oxide (AZO), and tin oxide (SnO). The solar module  300  further includes a photovoltaic (PV) layer  320  formed over the front contact layer  310  and a back contact layer  350  formed over the PV layer  320 . 
     The PV layer  320  may include a plurality of silicon film layers that includes one or more p-i-n junctions for converting energy from incident photons into electricity through the PV effect. In one configuration, the PV layer  320  comprises a first p-i-n junction having a p-type amorphous silicon layer, and intrinsic type amorphous silicon layer formed over the p-type amorphous silicon layer, and an n-type amorphous silicon layer formed over the intrinsic type amorphous silicon layer. In one example, the p-type amorphous silicon layer is formed to a thickness between about 60 Å and about 300 Å, the intrinsic type amorphous silicon layer is formed to a thickness between about 1500 Å and about 3500 Å, and the n-type amorphous semiconductor layer is formed to a thickness between about 100 Å and about 500 Å. In one embodiment, instead of the n-type amorphous silicon layer, an n-type microcrystalline semiconductor layer is formed to a thickness between about 100 Å and about 400 Å. 
     In another configuration, the PV layer  320  further comprises a second p-i-n junction over the first p-i-n junction. In one example, the second p-i-n junction comprises a p-type microcrystalline silicon layer formed to a thickness from about 100 Å and about 400 Å, an intrinsic type microcrystalline silicon layer formed to a thickness between about 10,000 Å and about 30,000 Å over the p-type microcrystalline silicon layer, and an n-type amorphous silicon layer formed over the intrinsic type microcrystalline silicon layer at a thickness between about 100 Å and about 500 Å. 
     The back contact layer  350 , which is formed over the PV layer  320 , may include one or more conductive layers adapted to serve as a back electrode for the solar cells  312 . In one embodiment, the back contact layer  350  may comprise a series of conductive layers that may include metals and/or conductive transparent oxide layers. Examples of materials that may comprise the back contact layer  350  include, but are not limited to aluminum (Al), silver (Ag), titanium (Ti), chromium (Cr), gold (Au), copper (Cu), platinum (Pt), alloys thereof, or combinations thereof. In one embodiment, the back contact layer  350  comprises a transparent conducting oxide (TCO) layer that is disposed over the PV layer  320  and one or more metal layers formed over the TCO layer. In one example, the TCO layer includes an aluminum zinc oxide (AZO) layer, and the one or more metal layers comprises an aluminum layer and a nickel vanadium alloy layer that has a thickness between about 1000 Å and about 3000 Å. In another example, the back contact layer  350  comprises an aluminum and nickel vanadium multilayer film that has a thickness between about 1000 Å and about 3000 Å. 
     Three scribing steps may be performed to produce trenches P 1 , P 2 , and P 3 , which are required to form a high efficiency solar cell device, such as the solar module  300 . Although formed together on the substrate  302 , the individual cells  312  are isolated from each other by the insulating trench P 3  formed in the back contact layer  350  and the PV layer  320 . In addition, the trench P 2  is formed in the PV layer  320  so that the back contact layer  350  is in electrical contact with the front contact layer  310 . In one embodiment, the insulating trench P 1  is formed by laser removal of a portion of the front contact layer  310  prior to the deposition of the PV layer  320  and the back contact layer  350 . Similarly, in on embodiment, the trench P 2  is formed in the PV layer  320  by the laser scribe removal of a portion of the PV layer  320  prior to the deposition of the back contact layer  350 . Finally, in one embodiment, the trench P 3  is formed by the laser removal of portions of the back contact layer  350  and the PV layer  320 . 
     The lines of trenches P 1 , P 2 , and P 3  are typically formed by a pulsed laser source capable of a frequency below about 80 kHz. The laser source is typically pulsed at a desired frequency as the substrate  302  is linearly translated, resulting in a series of overlapping regions or “spots” of ablated material in the desired layer on the substrate  302 . In conventional laser scribing of the P 1  trench, a 1064 nm laser source is pulsed at a frequency of about 60 kHz as the substrate  302  is linearly translated at a rate of about 1 m/s. In contrast, the formation of the P 2  and P 3  trenches are typically provided by pulsing a 532 nm laser at a frequency of about 20 kHz as the substrate  302  is linearly translated at a rate of about 1 m/s. Using conventional laser tools and laser pulsing techniques demands the use of a different wavelength laser for ablating the front contact layer material than the PV layer material or the back contact layer material to achieve reasonable throughput in the solar cell formation process. For instance, the use of a conventional 532 nm wavelength laser and conventional pulsing techniques on the front contact layer  310  does not result in fully ablated lines of trenches P 1  because the material (e.g., TCO) of which the front contact layer  310  is comprised, absorbs very little energy at wavelengths around 532 nm. In contrast, the use of a 1064 wavelength laser during the formation of the P 2  and P 3  trenches would result in unacceptable removal of the front contact layer  310 . 
     To avoid confusion relating to the actions specifically performed on the substrates  302  in the following description, a substrate  302  having one or more of the deposited layers (e.g., the front contact layer  310 , the PV layer  320 , or the back contact layer  350 ) and/or one or more internal electrical connections (e.g., side buss  314 , cross-buss  316 ) disposed thereon is referred to as a device substrate  303 . Similarly, a device substrate  303  that has been bonded to a back glass substrate using a bonding material is referred to as a composite solar cell structure  304 . 
     General Solar Module Formation 
     Referring to  FIGS. 1 and 2 , the process sequence  100  generally starts at step  102  in which a substrate  302  is loaded into a loading module  202  found in the solar module production line  200 . In one embodiment, the substrates  302  are received in a “raw” state where the edges, overall size, and/or cleanliness of the substrates  302  are not well controlled. Receiving “raw” substrates  302  reduces the cost to prepare and store substrates  302  prior to forming a solar device and thus reduces the solar cell device cost, facilities costs, and production costs of the finally formed solar cell device. However, typically, it is advantageous to receive “raw” substrates  302  that have a transparent conducting oxide (TCO) layer (e.g., front contact layer  310 ) already deposited on a surface of the substrate  302  before it is received into the system in step  102 . If a conductive layer is not deposited on the surface of the “raw” substrates then a front contact deposition step (step  107 ), which is discussed below, needs to be performed on a surface of the substrate  302 . 
     In one embodiment, each substrate  302  is received with a unique, reference designator formed thereon. In one embodiment, the reference designator comprises a unique, individual marking, such as a barcode or other identification marking, which is assigned to each substrate  302 . In one embodiment, the reference designator may be printed on or scribed into the substrate  302 . In one embodiment, the reference designator may be scribed into the front contact layer  310  already deposited on a surface of the substrate  302  before it is received into the production line  200 . In one embodiment, the reference designator may be located in an edge region of the substrate  302 / 303 . In one embodiment, the reference designator is read via a reading device (not shown), such as a barcode or other optical reading device, during or after loading the substrate  302 / 303  into the loading module  202 . The reference designator is then subsequently read at various locations throughout the production line  200 , and the identification information communicated to the system controller  290 , where it is correlated with other processing information and stored. The system controller  290  then uses the identification information provided on the reference designator to track the movement of each substrate  302 / 303 , control the movement and positioning of each substrate  302 / 303  in the production line  200 , and control the processes performed on each individual substrate  302 / 303 . 
     Referring to  FIGS. 1 and 2 , in one embodiment, prior to performing step  108  the substrate  302  is transported to a front end processing module (not illustrated in  FIG. 2 ) in which a front contact formation step  107  is performed on the substrate  302 . In one embodiment, the front end processing module is similar to the processing module  218  discussed below. In step  107 , one or more substrate front contact formation steps may include one or more preparation, etching and/or material deposition steps that are used to form the front contact regions on a bare solar cell substrate  302 . In one embodiment, step  107  generally comprises one or more physical vapor deposition (PVD) steps that are used to form the front contact region on a surface of the substrate  302 . In one embodiment, the front contact region contains a transparent conducting oxide (TCO) layer that may contain metal element selected from a group consisting of zinc (Zn), aluminum (Al), indium (In), and tin (Sn). In one example, a zinc oxide (ZnO) is used to form at least a portion of the front contact layer. In one embodiment, the front end processing module is an ATON™ PVD 5.7 tool available from Applied Materials in Santa Clara, Calif. in which one or more processing steps are performed to deposit the front contact formation steps. In another embodiment, one or more CVD steps are used to form the front contact region on a surface of the substrate  302 . 
     Next, the device substrate  303  is transported via the automation device  281  to a common scribe module  500 , which comprises a plurality of laser scribing tools  600 . In one embodiment, as the device substrate  303  enters the common scribe module  500 , its reference designator is read and communicated to the system controller  290 . The system controller  290  then controls the transport of the device substrate, on the automation device  281 , to one of the scribe tools  600  within the scribe module  500 . Since each of the scribe tools  600  is physically identical, the system controller  290  determines which of the scribe tools  600  is available and sends commands to the automation device  281  to transport the device substrate  303  to the available laser scribe tool  600 . The system controller  290  then sends commands to the specific scribe tool  600  to perform a front contact isolation step  108  on the device substrate  303  to electrically isolate different regions of the device substrate  303  surface from each other. 
     In the front contact isolation step  108 , the system controller  290  selects and controls process parameters of the scribe tool  600  to perform laser scribing of a series of lines of trenches P 1  into the front contact layer  310  of the device substrate  303 . In one embodiment, the system controller  290  determines the process parameters based on the location from which the device substrate  303  is received. In one embodiment, the laser scribe tool  600  comprises a fiber based pulsed amplifier laser configured to emit light at a wavelength from about 510 nm to about 560 nm, such as 532 nm. In one embodiment, the system controller  290  controls the laser pulse frequency of the fiber laser within the scribe tool  600  to at least about 300 kHz or greater. In one embodiment, the system controller  290  controls the laser power output between about 5 W and about 10 W. In one embodiment, the system controller  290  controls the laser pulse width between about 2 ns and about 30 ns. In one embodiment, the system controller  290  controls the laser pulse width to 4.2 ns. In one embodiment, the system controller  290  controls the scan speed between about 1 m/s and about 5 m/s, such as about 2.5 m/s. In one embodiment, the system controller  290  controls the laser spot size to about 50 μm or less. In one embodiment, the system controller sets and controls the spacing of the lines of trenches P 1 . The common scribe module  500  and the scribe tools  600  contained therein are described in more detail below with respect to FIGS.  5  and  6 A- 6 D. 
     Next, the device substrate  303  is transported out of the common scribe module  500  and into a processing module  212  in which step  112 , which comprises one or more photovoltaic deposition steps, is performed on the device substrate  303 . In step  112 , the one or more photovoltaic deposition steps may include one or more preparation, etching, and/or material deposition steps that are used to form the various regions of the solar cell device. Step  112  generally comprises a series of sub-processing steps that are used to form the PV layer  320  of the solar module  300 . In one embodiment, the PV layer  320  comprises one or more p-i-n junctions including amorphous silicon and/or microcrystalline silicon materials. In general, the one or more processing steps are performed in one or more cluster tools (e.g., cluster tools  212 A- 212 D) found in the processing module  212  to form one or more layers in the solar cell device formed on the device substrate  303 . 
     In one embodiment, each cluster tool  212 A- 212 D comprises a load lock chamber “A” and a plurality of processing chambers “B”-“H”. In one embodiment, one of the process chambers “B”-“H” is configured to deposit a p-type silicon layer(s) of a PV layer  320  of a solar cell device and the remaining processing chambers “B”-“H” are each configured to deposit both the intrinsic type silicon layer(s) and the n-type silicon layer(s) of the PV layer. In one embodiment, the intrinsic type silicon layer(s) and the n-type silicon layer(s) of the PV layer  320  may be deposited in the same chamber without performing a passivation process, which is used to minimize cross-contamination between the deposited layers, in between the deposition steps. 
     In one embodiment, in cases where the solar cell device is formed to include multiple p-i-n junctions, such as a tandem junction type of the solar cell, the cluster tool  212 A in the processing module  212  may be adapted to form the first p-i-n junction and at least one of the cluster tools  212 B- 212 D are configured to form the second p-i-n junction. 
     In one embodiment, the reference designator on the device substrate  303  is read prior to entering and/or within the processing module  212 , and identification information is communicated to the system controller  290 . In one embodiment, the identification information is used by the system controller  290  to track the device substrate  303  and control the processes performed thereon within the processing module  212 . 
     Next, the device substrate  303  is transported back to the common scribe module  500  via the automation device  281 . In one embodiment, as the device substrate  303  enters the common scribe module  500 , its reference designator is again read and communicated to the system controller  290 . The system controller  290  then controls the transport of the device substrate  303 , on the automation device  281 , to one of the scribe tools  600  within the scribe module  500 . Again, since each of the scribe tools  600  is physically identical, the system controller  290  determines which of the scribe tools  600  is available and sends commands to the automation device  281  to transport the device substrate  303  to the available laser scribe tool  600 . The system controller  290  then sends commands to the specific scribe tool  600  to perform an interconnect formation step  116  on the device substrate  303  to isolate different regions of the device substrate  303  surface from each other. In one embodiment, the device substrate  303  is transported via a crossover conveyor  281 A to allow the device substrate  303  to be transferred one of the scribe tools  600  for processing in the same direction as the previous and subsequent scribing processes. 
     In the interconnect formation step  116 , the system controller  290  selects and controls process parameters of the scribe tool  600  to perform laser scribing of a series of lines of trenches P 2  into the PV layer  320  of the device substrate  303 . In one embodiment, the system controller  290  determines the process parameters based on the location from which the device substrate  303  is received. In one embodiment, the laser scribe tool  600  comprises a fiber based pulsed amplifier laser configured to emit light at a wavelength from about 510 nm to about 560 nm, such as 532 nm. In one embodiment, the system controller  290  controls the laser pulse frequency of the fiber laser within the scribe tool  600  to between about 15 kHz and about 30 kHz, such as about 20 kHz. In one embodiment, the system controller  290  controls the laser power output from about 0.2 W to about 1 W. In one embodiment, the system controller  290  controls the laser pulse width between about 1 ns and about 30 ns. In one embodiment, the system controller  290  controls the laser pulse width to 4.2 ns. In one embodiment, the system controller  290  controls the scan speed between about 0.5 m/s and about 1.5 m/s, such as about 0.83 m/s. In one embodiment, the system controller  290  controls the laser spot size to about 50 μm or less. In one embodiment, the system controller sets and controls the spacing of the lines of trenches P 2 , such that they are appropriately spaced from the lines of trenches P 1 . The common scribe module  500  and the scribe tools  600  contained therein are described in more detail below with respect to FIGS.  5  and  6 A- 6 D. 
     Next, the device substrate  303  is transported to the processing module  218  in which a back contact formation step  118  is performed on the device substrate  303 . In step  118 , one or more substrate back contact formation steps are performed, which may include one or more preparation, etching, and/or material deposition steps that are used to form the back contact regions of the solar cell device. In one embodiment, step  118  generally comprises one or more PVD steps that are used to form the back contact layer  350  on the surface of the device substrate  303 . In one embodiment, the one or more PVD steps are used to form a back contact region that contains a metal layer selected from a group consisting of zinc (Zn), tin (Sn), aluminum (Al), copper (Cu), silver (Ag), nickel (Ni), and vanadium (V). In one example, a zinc oxide (ZnO) or nickel vanadium alloy (NiV) is used to form at least a portion of the back contact layer  350 . In one embodiment, the one or more processing steps are performed using an ATON™ PVD 5.7 tool available from Applied Materials in Santa Clara, Calif. In another embodiment, one or more CVD steps are used to form the back contact layer  350  on the surface of the device substrate  303 . In one embodiment, the reference designator on the device substrate  303  is read prior to entering and/or within the processing module  218 , and identification information is communicated to the system controller  290 . In one embodiment, the identification information is used by the system controller  290  to track the device substrate  303  and control the processes performed thereon within the processing module  218 . 
     Next, the device substrate  303  is transported back to the common scribe module  500  via the automation device  281 . In one embodiment, as the device substrate  303  enters the common scribe module  500 , its reference designator is again read and communicated to the system controller  290 . The system controller  290  then controls the transport of the device substrate  303 , on the automation device  281 , to one of the scribe tools  600  within the scribe module  500 . Again, since each of the scribe tools  600  is physically identical, the system controller  290  determines which of the scribe tools  600  is available and sends commands to the automation device  281  to transport the device substrate  303  to the available laser scribe tool  600 . The system controller  290  then sends commands to the specific scribe tool  600  to perform a back contact isolation step  120  on the device substrate  303  to isolate different regions of the device substrate  303  surface from each other. 
     In the back contact isolation step  120 , the system controller  290  selects and controls process parameters of the scribe tool  600  to perform laser scribing of a series of lines of trenches P 3  into the back contact layer  350  of the device substrate  303  to isolate regions of the plurality of solar cells  312  contained on the surface of the device substrate from each other. In one embodiment, the system controller  290  determines the process parameters based on the location from which the device substrate  303  is received. In one embodiment, the laser scribe tool  600  comprises a fiber based pulsed amplifier laser configured to emit light at a wavelength from about 510 nm to about 560 nm, such as 532 nm. In one embodiment, the system controller  290  controls the laser pulse frequency of the fiber laser within the scribe tool  600  to between about 15 kHz and about 30 kHz, such as about 20 kHz. In one embodiment, the system controller  290  controls the laser power output from about 0.2 W to about 1 W. In one embodiment, the system controller  290  controls the laser pulse width between about 1 ns and about 30 ns. In one embodiment, the system controller  290  controls the laser pulse width to 4.2 ns. In one embodiment, the system controller  290  controls the scan speed between about 0.5 m/s and about 1.5 m/s, such as about 0.83 m/s. In one embodiment, the system controller  290  controls the laser spot size to about 50 μm or less. In one embodiment, the system controller sets and controls the spacing of the lines of trenches P 3 , such that they are appropriately spaced from the lines of trenches P 1  and P 2 . The common scribe module  500  and the scribe tools  600  contained therein are described in more detail below with respect to FIGS.  5  and  6 A- 6 D. 
     The device substrate  303  is next transported to the seamer/edge deletion module  226  in which a substrate surface and edge preparation step  126  is used to prepare various surfaces of the device substrate  303  to prevent yield issues later on in the process. In one embodiment of step  126 , the device substrate  303  is inserted into seamer/edge deletion module  226  to prepare the edges of the device substrate  303  to shape and prepare the edges of the device substrate  303 . Damage to the device substrate  303  edge can affect the device yield and the cost to produce a usable solar cell device. In another embodiment, the seamer/edge deletion module  226  is used to remove deposited material from the edge of the device substrate  303  (e.g., 10-12 mm) to provide a region that can be used to form a reliable seal between the device substrate  303  and the backside glass (i.e., steps  134 - 136  discussed below). Material removal from the edge of the device substrate  303  may also be useful to prevent electrical shorts in the final formed solar module. 
     In one embodiment, a diamond impregnated belt is used to grind the deposited material from the edge regions of the device substrate  303 . In another embodiment, a grinding wheel is used to grind the deposited material from the edge regions of the device substrate  303 . In another embodiment, dual grinding wheels are used to remove the deposited material from the edge of the device substrate  303 . In yet another embodiment, a laser ablation technique is used to remove the deposited material from the edge of the device substrate  303 . In one example, a high power infrared wavelength ND:YAG laser having a spot size of about 1 mm is used to ablate a portion of the material from the edge regions of the device substrate  303 . In one aspect, the seamer/edge deletion module  226  is used to round or bevel the edges of the device substrate  303  by use of shaped grinding wheels, angled and aligned belt sanders, and/or abrasive wheels. 
     Next the device substrate  303  is transported to the pre-screen module  227  in which optional pre-screen steps  127  are performed on the device substrate  303  to assure that the devices formed on the substrate surface meet a desired quality standard. In step  127 , a light emitting source and probing device are used to measure the output of the formed solar cell device by use of one or more substrate contacting probes. If the module  227  detects a defect in the formed device it can take corrective actions or the solar cell can be scrapped. 
     Next the substrate  303  is transported to a bonding wire attach module  231  in which step  131 , or a bonding wire attach step, is performed on the substrate  303 . Step  131  is used to attach the various wires/leads required to connect the various external electrical components to the formed solar cell device. Typically, the bonding wire attach module  231  is an automated wire bonding tool that is advantageously used to reliably and quickly form the numerous interconnects that are often required to form the large solar cells formed in the production line  200 . In one embodiment, the bonding wire attach module  231  is used to form the side-buss  314  ( FIG. 3 ) and cross-buss  316  on the formed back contact layer  350  (step  118 ). In this configuration the side-buss  314  may be a conductive material that can be affixed, bonded, and/or fused to the back contact layer  350  found in the back contact region to form a good electrical contact. In one embodiment, the side-buss  314  and cross-buss  316  each comprise a metal strip, such as copper tape, a nickel coated silver ribbon, a silver coated nickel ribbon, a tin coated copper ribbon, a nickel coated copper ribbon, or other conductive material that can carry the current delivered by the solar cell and be reliably bonded to the metal layer in the back contact region. In one embodiment, the metal strip is between about 2 mm and about 10 mm wide and between about 1 mm and about 3 mm thick. The cross-buss  316 , which is electrically connected to the side-buss  314  at the junctions, can be electrically isolated from the back contact layer(s) of the solar cell by use of an insulating material, such as an insulating tape. The ends of each of the cross-busses  316  generally have one or more leads that are used to connect the side-buss  314  and the cross-buss  316  to the electrical connections found in a junction box  308 , which is used to connect the formed solar cell to the other external electrical components. 
     In the next step, step  132 , a bonding material and “back glass” substrate are prepared for delivery into the solar cell formation process (i.e., process sequence  100 ). The preparation process is generally performed in the glass lay-up module  232 , which generally comprises a material preparation module  232 A, a glass loading module  232 B, a glass cleaning module  232 C, and a glass inspection module  232 D. The back glass substrate is bonded onto the device substrate  303  formed in steps  102 - 131  above by use of a laminating process (step  134  discussed below). In general, step  132  requires the preparation of a polymeric material that is to be placed between the back glass substrate and the deposited layers on the device substrate  303  to form a hermetic seal to prevent the environment from attacking the solar cell during its life. Referring to  FIG. 2 , step  132  generally comprises a series of sub-steps in which a bonding material is prepared in the material preparation module  232 A, the bonding material is then placed over the device substrate  303 , and the back glass substrate is loaded into the loading module  232 B. The back glass substrate is washed by the cleaning module  232 C. The back glass substrate is then inspected by the inspection module  232 D, and the back glass substrate is placed over the bonding material and the device substrate  303 . 
     In the next sub-step of step  132 , the back glass substrate is transported to the cleaning module  232 C in which a substrate cleaning step, is performed on the substrate to remove any contaminants found on the surface of the substrate. Common contaminants may include materials deposited on the substrate during the substrate forming process (e.g., glass manufacturing process) and/or during shipping of the substrates. Typically, the cleaning module  232 C uses wet chemical scrubbing and rinsing steps to remove any undesirable contaminants as discussed above. 
     The prepared back glass substrate is then positioned over the bonding material and partially device substrate  303  by use of an automated robotic device. 
     Next the device substrate  303 , the back glass substrate, and the bonding material are transported to the bonding module  234  in which step  134 , or lamination steps are performed to bond the backside glass substrate to the device substrate formed in steps  102 - 132  discussed above. In step  134 , a bonding material, such as Polyvinyl Butyral (PVB) or Ethylene Vinyl Acetate (EVA), is sandwiched between the backside glass substrate and the device substrate  303 . Heat and pressure are applied to the structure to form a bonded and sealed device using various heating elements and other devices found in the bonding module  234 . The device substrate  303 , the back glass substrate and bonding material thus form a composite solar cell structure  304  that at least partially encapsulates the active regions of the solar cell device. In one embodiment, at least one hole formed in the back glass substrate remains at least partially uncovered by the bonding material to allow portions of the cross-buss  316  or the side buss  314  to remain exposed so that electrical connections can be made to these regions of the solar cell structure  304  in future steps (i.e., step  138 ). 
     Next the composite solar cell structure  304  is transported to the autoclave module  236  in which step  136 , or autoclave steps are performed on the composite solar cell structure  304  to remove trapped gases in the bonded structure and assure that a good bond is formed during step  136 . In step  136 , a bonded solar cell structure  304  is inserted in the processing region of the autoclave module where heat and high pressure gases are delivered to reduce the amount of trapped gas and improve the properties of the bond between the device substrate  303 , back glass substrate, and bonding material. The processes performed in the autoclave are also useful to assure that the stress in the glass and bonding layer (e.g., PVB layer) are more controlled to prevent future failures of the hermetic seal or failure of the glass due to the stress induced during the bonding/lamination process. In one embodiment, it may be desirable to heat the device substrate  303 , back glass substrate, and bonding material to a temperature that causes stress relaxation in one or more of the components in the formed solar cell structure  304 . 
     Next the solar cell structure  304  is transported to the junction box attachment module  238  in which junction box attachment steps  138  are performed on the formed solar cell structure  304 . The junction box attachment module  238 , used during step  138 , is used to install a junction box  308  ( FIG. 3 ) on a partially formed solar module. The installed junction box  308  acts as an interface between the external electrical components that will connect to the formed solar module, such as other solar modules or a power grid, and the internal electrical connections points, such as the leads, formed during step  131 . In one embodiment, the junction box  308  contains one or more connection points so that the formed solar module can be easily and systematically connected to other external devices to deliver the generated electrical power. 
     Next, the solar cell structure  304  is transported to the device testing module  240  in which device screening and analysis steps  140  are performed on the solar cell structure  304  to assure that the devices formed on the solar cell structure  304  surface meet desired quality standards. In one embodiment, the device testing module  240  is a solar simulator module that is used to qualify and test the output of the one or more formed solar cells. In step  140 , a light emitting source and probing device are used to measure the output of the formed solar cell device by use of one or more automated components that are adapted to make electrical contact with terminals in the junction box  308 . If the module detects a defect in the formed device it can take corrective actions or the solar cell can be scrapped. 
     Next the solar cell structure  304  is transported to the support structure module  241  in which support structure mounting steps  141  are performed on the solar cell structure  304  to provide a complete solar cell device that has one or more mounting elements attached to the solar cell structure  304  formed using steps  102 - 140  to a complete solar cell device that can easily be mounted and rapidly installed at a customer&#39;s site. 
     Next the solar cell structure  304  is transported to the unload module  242  in which step  142 , or device unload steps are performed on the substrate to remove the formed solar cells from the solar module production line  200 . 
     Common Laser Scribe Module and Laser Scribe Tools 
       FIG. 5  is a schematic plan view of the common scribe module  500  according to one embodiment of the present invention. The common scribe module  500  may include a plurality of reading devices  510  located at entry and exit points of the common scribe module  500 . In one embodiment, the reading devices  510  are bar code readers, or other optical reading devices, for reading the unique reference designator supplied on each device substrate  303  and communicating identification information associated with the reference designator to the system controller  290 . The common scribe module  500  also includes the automation device  281  for generally transporting the device substrate  303  through the common scribe module  500 . The automation device  281  may include a plurality of rollers (not shown), actuators (not shown), and other conventional conveyor components, which are all controlled by the system controller  290 . As previously set forth, the common scribe module  500  also includes a plurality of laser scribe tools  600 . Although  FIG. 5  depicts the common scribe module  500  having three laser scribe tools  600 , this is not intended to limit the scope of the invention. In other embodiments, the common scribe module  500  may contain more or fewer scribe tools  600  depending on the desired throughput of the production line  200 , such as depicted in  FIG. 2 , for instance. 
       FIG. 6A  is a schematic plan view and  FIG. 6B  is a schematic, cross-sectional view of a laser scribe tool  600  that may be used for laser scribing a series of trenches (i.e., P 1 , P 2 , or P 3 ) in one or more material layers (i.e., front contact layer  310 , PV layer  320 , or back contact layer  350 ) deposited on the solar cell substrate  302 . In one embodiment, the laser scribe tool  600  generally includes a substrate handling system  610 , one or more laser devices  620 , and an exhaust assembly  630 , all coordinated and controlled by the system controller  290 . 
     In general operation, a device substrate  303  is transferred into the laser scribe tool  600  following a path A. In one embodiment, the device substrate  303  is oriented with the surface having one or more layers (e.g., front contact layer  310 , PV layer  320 , back contact layer  350 ) facing upwardly. The device substrate  303  is then passed over the laser devices  620  one or more times while a series of trenches (i.e., P 1 , P 2 , or P 3 ) are scribed into the device substrate  303 . The device substrate  303  then exits the laser scribe tool  600  following path A o . Although  FIG. 6A  depicts the substrate  303  following the path A i  to A o , the substrate  303  may follow a path in the opposite direction A o  to A i , depending on commands received from the system controller  290 . 
       FIG. 6C  is a schematic depiction of the laser device  620 . In one embodiment, each laser device  620  comprises a laser radiation source  621  and a focusing optical module  623  disposed therein. The laser radiation source  621  includes a pumped laser source  622  that emits a light beam to an optical fiber  624  disposed in the focusing optical module  623 . The optical fiber  624  serves as a gain medium that is configured to receive a pulse of energy delivered from the pumped laser source  622  having an initial pulse wavelength and an initial pulse energy. When received by the optical fiber  624 , the pulse of energy from the pumped laser source  622  is amplified and emitted toward the desired region of the device substrate  303 . Suitable examples for the gain medium may be fiber doped with one or more rare earth metals (e.g., actinides, lanthanides), such as erbium, neodymium, ytterbium, thulium, praseodymium, holmium, dysprosium, samarium, or the like. Light emitting atoms, such as rare earth metals, are doped into a core of the optical fiber  624  that confines the light that the atoms emit. A pair of mirrors  625   a  and  625   b  may be disposed on each end of the optical fiber  624  to confine the pumped radiation inside the fiber gain medium and allow the emitted radiation to exit therefrom. 
     In one embodiment, the optical fiber  624  may include a core  626 , an internal cladding  627 , and an outer cladding  628  as depicted in the schematic, cross-sectional view shown in  FIG. 6D . The core  626  may be formed from a ceramic material that has the rare earth metals doped therein. Suitable ceramic containing materials may include silica, silicon containing material, silicon carbon, silicon oxide, and the like. In one embodiment, the rare earth metals selected to be doped into the core  626  are erbium or ytterbium. The internal cladding  627  may comprise a material having a first refractive index, and the outer cladding  628  may be made from a material having a second refractive index different from the first refractive index. A large refractive index contrast between the internal cladding  627  and the outer cladding  628  may enhance light reflection when transmitting through the optical fiber  624 , thereby amplifying the laser emitting efficiency. In one embodiment, the internal cladding  627  and the outer cladding  628  may be fabricated from suitable ceramic materials, such a silica glass, silicon carbide, or the like. 
     Referring back to  FIG. 6C , the focusing optical module  623  may also include one or more collimators to collimate radiation from the pumped laser source  622  into a substantially parallel beam. This collimated radiation beam is then focused by at least one lens  629  into a line of radiation directed at the desired region of the device substrate  303 . The lens  629  may be any suitable lens, or series of lenses, capable of focusing radiation into a line or spot. In one embodiment, the lens  629  is a cylindrical lens. Alternatively, the lens  629  may be one or more concave lenses, convex lenses, plane mirrors, concave mirrors, convex mirrors, refractive lenses, diffractive lenses, Fresnel lenses, gradient index lenses, or the like. 
     Referring back to  FIGS. 6A and 6B , the system controller  290  controls the power, energy, pulse width, and pulse frequency (among other parameters) of the delivery of energy used to scribe the desired trenches (e.g., P 1 , P 2 , or P 3 ) into the respective layer (e.g., front contact layer  310 , PV layer  320 , or back contact layer  350 ) in the device substrate  303 . In one embodiment, the one or more laser devices  620  are located below the device substrate  303 . In one embodiment, a portion of the exhaust assembly  630  is located above the device substrate  303 , in order to effectively exhaust material that is ablated or otherwise removed from the device substrate  303  via the respective laser device  620 . 
     In one embodiment, the substrate handling system  610  includes a support structure  605  that is positioned beneath the device substrate  303  and is adapted to support and retain the various components used to perform laser scribing processes on the device substrate  303 . In one embodiment, the substrate handling system  610  includes a conveyor system  612  that has a plurality of conventional, automated conveyor belts for positioning and transferring the device substrate  303  within the laser scribe tool  600  in a controlled and automated fashion. 
     In one embodiment, the substrate handling system  610  further includes one or more substrate grippers  614  for retaining, guiding, and moving the device substrate  303  during laser scribing processes. The substrate grippers  614  are used to grip the edges of the device substrate  303  and include an actuator, such as a linear motor, to translate the device substrate  303  in the Y and −Y directions while the laser devices  620  form the trenches (e.g., P 1 , P 2 , or P 3 ) into the desired layers of the device substrate  303 . 
     Referring to  FIG. 5 , as a device substrate  303  is received into the common scribe module  500 , the reference designator assigned to the device substrate  303  is read by the reading device  510 , and identification information associated with the reference designator, and thus the device substrate  303  is communicated to the system controller  290 . From this information, the system controller  290  may determine which processes the device substrate  303  has undergone, and which scribing process is needed. The system controller  290  may then determine which scribe tool  600  is available and send commands to the automation device  281  to transport the device substrate  303  to the available scribe tool  600 . The system controller  290  may also set and control the parameters (e.g., power, pulse frequency, pulse width, pattern of scribe lines) of the laser scribe tool  600  in order to scribe the appropriate lines of trenches (P 1 , P 2 , or P 3 ) in the appropriate layer ( 310 ,  320 ,  350 ) of the device substrate  303 . In one embodiment, the system controller  290  determines the process parameters based on the location from which the device substrate  303  is received. Once the laser scribing procedure ( 108 ,  116 ,  120 ) is completed, the device substrate  303  is transported out of the common scribe module  500  via the automation device  281  controlled by the system controller  290 . 
     As previously mentioned, current state of the art laser ablation techniques used for forming trenches in the front contact layer  310  (or TCO layer) of thin film solar cells require the use of a higher wavelength laser, such as 1064 nm, than that used for the PV layer  320  and back contact layer  350 . This is because the lower wavelength lasers, such as conventional 532 nm wavelength laser, are not capable of fully ablating a spot of the TCO material layer with a single pulse. In contrast, the configuration and processes described above with respect to the present invention allow the use of a 532 nm programmable fiber laser at significantly higher pulse frequencies to remove trenches P 1  of the TCO material in a single pass. This is possible because the higher pulse frequency capability provides multiple pulses of energy at the same “spot” on the substrate  302 , effectively “chipping away” at the TCO layer until the entire “spot” is ablated. Thus, the use of such apparatus and techniques allow the use of a plurality of identical lasers, such as 532 nm wavelength lasers, to scribe lines of the trenches P 1 , P 2 , and P 2  in the multiple layers of the device substrate  303  without sacrificing throughput of the overall system. 
     While the foregoing is directed to embodiments of the present 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.