Patent Application
20100273279
1. Field of the Invention
Embodiments of the present invention generally relate to a production line used to form multiple sized solar cell devices.
2. Description of the Related Art
Photovoltaic (PV) devices or solar cells are devices which convert sunlight into direct current (DC) electrical power. Typical thin film type PV devices, or thin film solar cells, have 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. Solar cells may be tiled into larger solar arrays. The solar arrays are created by connecting a number of solar cells and joining them into panels with specific frames and connectors.
Typically, a thin film solar cell includes active regions, or photoelectric conversion units, and a transparent conductive oxide (TCO) film disposed as a front electrode and/or as a back electrode. The photoelectric conversion unit includes a p-type silicon layer, an n-type silicon layer, and an intrinsic type (i-type) silicon layer sandwiched between the p-type and n-type silicon layers. Several types of silicon films including microcrystalline silicon film (μc-Si), amorphous silicon film (a-Si), polycrystalline silicon film (poly-Si), and the like may be utilized to form the p-type, n-type, and/or i-type layers of the photoelectric conversion unit. The backside electrode may contain one or more conductive layers. There is a need for an improved process of forming a solar cell that has good interfacial contact, low contact resistance and provides a high overall electrical device performance.
With traditional energy source prices on the rise, there is a need for a low cost method of producing electricity using a low cost solar cell device. Conventional solar cell manufacturing processes are highly labor intensive and have numerous interruptions that can affect the production line throughput, solar cell cost, and device yield. For instance, particular solar cell device sizes are needed for particular applications. Conventional solar cell lines are either capable of producing only a single sized solar cell device or require significant downtime to manually convert the solar cell production line processes to accommodate a different substrate size and produce a different sized solar cell device. Thus, there is a need for a production line that is able to perform all phases of the fabrication process for producing multiple sized solar cell devices from a single large substrate.
In one embodiment of the present invention, a system for fabricating solar cell devices comprises a substrate receiving module that is adapted to receive a front substrate, a cluster tool having a processing chamber that is adapted to deposit a silicon-containing layer on a surface of the front substrate, a back contact deposition chamber configured to deposit a back contact layer on the silicon-containing layer, a bonding module configured to encapsulate the silicon-containing layer and the back contact layer between the front substrate and a back substrate into a composite structure, a sectioning module configured to section the composite structure into two or more sections, and a system controller for controlling and coordinating functions of each of the substrate receiving module, the cluster tool, the processing chamber, the back contact deposition chamber, the bonding module, and the sectioning module.
In another embodiment of the present invention, a system for fabricating solar cell devices comprises a substrate receiving module that is adapted to receive a front substrate, a cluster tool having a processing chamber that is adapted to deposit a silicon-containing layer on a surface of the front substrate, a back contact deposition chamber configured to deposit a back contact layer on the silicon-containing containing layer, a bonding module configured to encapsulate the silicon-containing layer and the back contact layer between the front substrate and a back substrate into a composite structure, a testing module configured to test performance characteristics of the composite structure, a sectioning module configured to section the tested composite structure into two or more sections, wherein the sectioning module comprises a composite structure positioning mechanism and a composite structure sectioning mechanism, and a system controller for controlling and coordinating functions of each of the substrate receiving module, the cluster tool, the processing chamber, the back contact deposition chamber, the bonding module, the testing module, and the sectioning module.
In yet another embodiment of the present invention, a method of processing a solar cell device cleaning a substrate to remove one or more contaminants from a surface of the substrate, depositing a photoabsorbing layer on the surface of the substrate, removing at least a portion of the photoabsorbing layer from a region on the surface of the substrate, depositing a back contact layer over the photoabsorbing layer on the substrate, removing at least a portion of the back contact layer and the photoabsorbing layer from a region on the surface of the substrate, bonding a back glass substrate to the substrate to form a composite structure, wherein the back contact layer and the photoabsorbing layer are bonded between the back glass substrate and the substrate, attaching one or more junction boxes to the composite structure, testing performance characteristics of the composite structure, and sectioning the composite structure into two or more sections.
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.
Embodiments of the present invention generally relate to a system used to form solar cell devices using processing modules adapted to perform one or more processes in the formation of the solar cell devices. In one embodiment, the system is adapted to form thin film solar cell devices by accepting a large unprocessed substrate and performing multiple deposition, material removal, cleaning, bonding, testing, and sectioning processes to form multiple complete, functional, and tested solar cell devices that can then be shipped to an end user for installation in a desired location to generate electricity.
In one embodiment, the system is capable of accepting a single large unprocessed substrate and producing multiple smaller solar cell devices. In one embodiment, the system is capable of changing the sizes of the solar cell devices produced from the single large substrate without manually moving or altering any of the system modules. While the discussion below primarily describes the formation of silicon thin film solar cell devices, this configuration is not intended to limit the scope of the invention since the apparatus and methods disclosed herein can also be used to form, test, and analyze other types of solar cell devices, such as III-V type solar cells, thin film chalcogenide solar cells (e.g., CIGS, CdTe cells), amorphous or nanocrystalline silicon solar cells, photochemical type solar cells (e.g., dye sensitized), crystalline silicon solar cells, organic type solar cells, or other similar solar cell devices.
In one embodiment, the system is generally an arrangement of automated processing modules and automation equipment used to form solar cell devices that are interconnected by an automated material handling system. In one embodiment, the system is a fully automated solar cell device production line that reduces or removes the need for human interaction and/or labor intensive processing steps to improve the device reliability, process repeatability, and cost of ownership of the formation process.
In one configuration, the system is adapted to form multiple silicon thin film solar cell devices from a single large substrate and generally comprises a substrate receiving module that is adapted to accept an incoming substrate, one or more absorbing layer deposition cluster tools having at least one processing chamber that is adapted to deposit a silicon-containing layer on a processing surface of the substrate, one or more back contact deposition chambers that are adapted to deposit a back contact layer on the processing surface of the substrate, one or more material removal chambers that are adapted to remove material from the processing surface of the substrate, an encapsulation device that is adapted to form a composite solar cell structure from the substrate, an autoclave module that is adapted to heat and expose the composite solar cell structure to a pressure greater than atmospheric pressure, a junction box attaching region to attach a connection element that allows the solar cell device to be connected to external components, one or more quality assurance modules adapted to test and qualify the formed solar cell device, and one or more sectioning modules used to section the formed solar cell device into multiple smaller solar cell devices. The one or more quality assurance modules may include a solar simulator, a parametric testing module, and a shunt bust and qualification module.
In general, a system controller 290 may be used to control one or more components found in the solar cell production line 200. The system controller 290 is generally designed to facilitate the control and automation of the overall solar cell 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 solar cell production line 200. In one embodiment, the system controller 290 also contains a plurality of programmable logic controllers (PLC'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 solar cell production line.
Examples of a solar cell 300 that can be formed using the process sequence(s) illustrated in
To improve light absorption by enhancing light trapping, the substrate and/or one or more of the thin films formed thereover may be optionally textured by wet, plasma, ion, and/or mechanical processes. For example, in the embodiment shown in
In one configuration, the first p-i-n junction 320 may comprise a p-type amorphous silicon layer 322, an intrinsic type amorphous silicon layer 324 formed over the p-type amorphous silicon layer 322, and an n-type microcrystalline silicon layer 326 formed over the intrinsic type amorphous silicon layer 324. In one example, the p-type amorphous silicon layer 322 may be formed to a thickness between about 60 Å and about 300 Å, the intrinsic type amorphous silicon layer 324 may be formed to a thickness between about 1,500 Å and about 3,500 Å, and the n-type microcrystalline silicon layer 326 may be formed to a thickness between about 100 Å and about 400 Å. The back contact layer 350 may include, but is not limited to a material selected from Al, Ag, Ti, Cr, Au, Cu, Pt, alloys thereof, and combinations thereof.
The first p-i-n junction 320 may comprise a p-type amorphous silicon layer 322, an intrinsic type amorphous silicon layer 324 formed over the p-type amorphous silicon layer 322, and an n-type microcrystalline silicon layer 326 formed over the intrinsic type amorphous silicon layer 324. In one example, the p-type amorphous silicon layer 322 may be formed to a thickness between about 60 Å and about 300 Å, the intrinsic type amorphous silicon layer 324 may be formed to a thickness between about 1,500 Å and about 3,500 Å, and the n-type microcrystalline silicon layer 326 may be formed to a thickness between about 100 Å and about 400 Å.
The second p-i-n junction 330 may comprise a p-type microcrystalline silicon layer 332, an intrinsic type microcrystalline silicon layer 334 formed over the p-type microcrystalline silicon layer 332, and an n-type amorphous silicon layer 336 formed over the intrinsic type microcrystalline silicon layer 334. In one example, the p-type microcrystalline silicon layer 332 may be formed to a thickness between about 100 Å and about 400 Å, the intrinsic type microcrystalline silicon layer 334 may be formed to a thickness between about 10,000 Å and about 30,000 Å, and the n-type amorphous silicon layer 336 may be formed to a thickness between about 100 Å and about 500 Å. The back contact layer 350 may include, but is not limited to, a material selected from Al, Ag, Ti, Cr, Au, Cu, Pt, alloys thereof, and combinations thereof.
As shown in
To avoid confusion relating to the actions specifically performed on the substrates 302 in the discussion below, a substrate 302 having one or more of the deposited layers (e.g., reference numerals 310-350) and/or one or more internal electrical connections (e.g., side buss 355, cross-buss 356) disposed thereon is generally referred to as a device substrate 303. Similarly, a device substrate 303 that has been bonded to a back glass substrate 361 using a layer of bonding material 360 is referred to as a composite solar cell structure 304. In general, configurations in which a single solar cell is formed across the entire substrate 302 are specifically noted. Otherwise, it is intended that the phrase “solar cell 300” generally signifies one of the two or more smaller solar cells (e.g., reference numerals 300A-300D in
Referring to
In one embodiment, the substrates 302 or 303 are loaded into the solar cell production line 200 in a sequential fashion, and thus do not use a cassette or batch style substrate loading system. A cassette style and/or batch loading type system that requires the substrates to be un-loaded from the cassette, processed, and then returned to the cassette before moving to the next step in the process sequence can be time consuming and decrease the solar cell production line throughput. The use of batch processing does not facilitate certain embodiments of the present invention, such as fabricating multiple solar cell devices from a single substrate. Additionally, the use of a batch style process sequence generally prevents the use of an asynchronous flow of substrates through the production line, which is believed to provide improved substrate throughput during steady state processing and when one or more modules are brought down for maintenance or due to a fault condition. Generally, batch or cassette based schemes are not able to achieve the throughput of the production line described herein during normal operation, or more particularly, when one or more processing modules are brought down for maintenance, since the queuing and loading of substrates can require a significant amount of overhead time.
In step 104, the surfaces of the substrate 302 are prepared to prevent yield issues later on in the process. In one embodiment of step 104, the substrate is inserted into a front end seaming module 204 that is used to prepare the edges of the substrate 302 or 303 to reduce the likelihood of damage, such as chipping or particle generation from occurring during the subsequent processes. Damage to the substrate 302 or 303 can affect device yield and the cost to produce a usable solar cell device. In one embodiment, the front end seaming module 204 is used to round or bevel the edges of the substrate 302 or 303. In one embodiment, a diamond impregnated belt or disc is used to grind the material from the edges of the substrate 302 or 303. In another embodiment, a grinding wheel, grit blasting, or laser ablation technique is used to remove the material from the edges of the substrate 302 or 303.
Next the substrate 302 or 303 is transported to the cleaning module 206, in which step 106, or a substrate cleaning step, is performed on the substrate 302 or 303 to remove any contaminants found on the surface of thereof. Common contaminants may include materials deposited on the substrate 302 or 303 during the substrate forming process (e.g., glass manufacturing process) and/or during shipping or storing of the substrates 302 or 303. Typically, the cleaning module 206 uses wet chemical scrubbing and rinsing steps to remove any undesirable contaminants.
In one example, the process of cleaning the substrate 302 or 303 may occur as follows. First, the substrate 302 or 303 enters a contaminant removal section of the cleaning module 206 from either a transfer table or an automation device 281. In general, the system controller 290 establishes the timing for each substrate 302 or 303 that enters the cleaning module 206. The contaminant removal section may utilize dry cylindrical brushes in conjunction with a vacuum system to dislodge and extract contaminants from the surface of the substrate 302. Next, a conveyor within the cleaning module 206 transfers the substrate 302 or 303 to a pre-rinse section, where spray tubes dispense hot de-ionized (DI) water at a temperature, for example, of 50° C. from a DI water heater onto a surface of the substrate 302 or 303. Commonly, since the device substrate 303 has a TCO layer disposed thereon, and since TCO layers are generally electron absorbing materials, DI water is used to avoid any traces of possible contamination and ionizing of the TCO layer. Next, the rinsed substrate 302, 303 enters a wash section. In the wash section, the substrate 302 or 303 is wet-cleaned with a brush (e.g., perlon) and hot water. In some cases a detergent (e.g., AlconoX™, Citrajet™, Detojet™, Transene™, and Basic H™), surfactant, pH adjusting agent, and other cleaning chemistries are used to clean and remove unwanted contaminants and particles from the substrate surface. A water re-circulation system recycles the hot water flow. Next, in a final rinse section of the cleaning module 206, the substrate 302 or 303 is rinsed with water at ambient temperature to remove any traces of contaminants. Finally, in a drying section, an air blower is used to dry the substrate 302 or 303 with hot air. In one configuration, a deionization bar is used to remove the electrical charge from the substrate 302 or 303 at the completion of the drying process.
In one embodiment of step 108, the TCO layer 310 is scribed to form separate, electrically isolated cells on the surface of the substrate 302. Contamination particles on the surface of the TCO layer 310 and/or on the bare surface of the substrate 302 can interfere with the scribing procedure. In laser scribing, for example, if the laser beam runs across a particle, it may be unable to scribe a continuous line, and a short circuit between cells may result. In addition, any particulate debris present in the scribed pattern and/or on the TCO layer 310 after scribing can cause shunting and non-uniformities between layers. Therefore, a well-defined and well-maintained process is needed to ensure that contamination is removed throughout the production process. In one embodiment, the cleaning module 206 is available from the Energy and Environment Solutions division of Applied Materials in Santa Clara, Calif.
Referring to
Next the device substrate 303 is transported to the scribe module 208 in which step 108, or a front contact isolation step, is performed on the device substrate 303 to electrically isolate different regions of the device substrate 303 surface from each other. In step 108, material is removed from the device substrate 303 surface by use of a material removal step, such as a laser ablation process. The success criteria for step 108 are to achieve good cell-to-cell and cell-to-edge isolation while minimizing the scribe area. In one embodiment, a Nd:vanadate (Nd:YVO4) laser source is used ablate material from the device substrate 303 surface to form lines that electrically isolate one region of the device substrate 303 from the next. In one embodiment, the laser scribe process performed during step 108 uses a 1064 nm wavelength pulsed laser to pattern the material disposed on the substrate 302 to isolate each of the individual cells (e.g., individual cells 382A and 382B) that make up the solar cell 300. In one embodiment, a 5.7 m2 substrate laser scribe module available from Applied Materials, Inc. of Santa Clara, Calif. is used to provide simple reliable optics and substrate motion for accurate electrical isolation of regions of the device substrate 303 surface. In another embodiment, a water jet cutting tool or diamond scribe is used to isolate the various regions on the surface of the device substrate 303.
In one aspect, it is desirable to assure that the temperature of the device substrates 303 entering the scribe module 208 are at a temperature in a range between about 20° C. and about 26° C. by use of an active temperature control hardware assembly that may contain a resistive heater and/or chiller components (e.g., heat exchanger, thermoelectric device). In one embodiment, it is desirable to control the device substrate 303 temperature to about 25±0.5° C.
Next, the device substrate 303 is transported to the cleaning module 210 in which step 110, or a pre-deposition substrate cleaning step, is performed on the device substrate 303 to remove any contaminants found on the surface of the device substrate 303 after performing the front contact isolation step (step 108). Typically, the cleaning module 210 uses wet chemical scrubbing and rinsing steps to remove any undesirable contaminants found on the device substrate 303 surface after performing the cell isolation step. In one embodiment, a cleaning process, similar to the processes described in step 106 above, is performed on the device substrate 303 to remove any contaminants on the surface(s) of the device substrate 303.
Next, the device substrate 303 is transported to the processing module 212 in which step 112, which comprises one or more photoabsorber deposition steps, is performed on the device substrate 303. In step 112, the one or more photoabsorber deposition steps may include one or more preparation, etching, and/or material deposition steps that are used to form various regions of the solar cell device. Step 112 generally comprises a series of sub-processing steps that are used to form one or more p-i-n junctions, such as the first p-i-n junction 320 and the second p-i-n junction 330. In one embodiment, the one or more p-i-n junctions comprise 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 212A-212D) found in the processing module 212 to form one or more layers on the device substrate 303. In one embodiment, the device substrate 303 is transferred to an accumulator 211A prior to being transferred to one or more of the cluster tools 212A-212D. In one embodiment, in cases where the solar cell device is formed to include multiple junctions, such as the tandem junction solar cell 300 illustrated in
In one embodiment of the process sequence 100, a cool down step, or step 113, is performed after step 112 has been performed. The cool down step is generally used to stabilize the temperature of the device substrate 303 to assure that the processing conditions seen by each device substrate 303 in the subsequent processing steps are repeatable. Generally, the temperature of the device substrate 303 exiting the processing module 212 could vary by many degrees Celsius and exceed a temperature of 50° C., which can cause variability in the subsequent processing steps and solar cell performance.
In one embodiment, the cool down step 113 is performed in one or more of the substrate supporting positions found in one or more accumulators 211. In one configuration of the production line, as shown in
Next, the device substrate 303 is transported to the scribe module 214 in which an interconnect formation step, or step 114, is performed on the device substrate 303 to electrically isolate various regions of the device substrate 303 surface from each other. In step 114, material is removed from the device substrate 303 surface by use of a material removal step, such as a laser ablation process. In one embodiment, an Nd:vanadate (Nd:YVO4) laser source is used ablate material from the substrate surface to form lines that electrically isolate one individual cell from the next. In one embodiment, a 5.7 m2 substrate laser scribe module available from Applied Materials, Inc. is used to perform the accurate scribing process. In one embodiment, the laser scribe process performed during step 114 uses a 532 nm wavelength pulsed laser to pattern the material disposed on the device substrate 303 to isolate the individual cells that make up the solar cell 300. As shown in
In one aspect, it is desirable to assure that the temperature of the device substrates 303 entering the scribe module 214 are at a temperature in a range between about 20° C. and about 26° C. by use of an active temperature control hardware assembly that may contain a resistive heater and/or chiller components (e.g., heat exchanger, thermoelectric device). In one embodiment, it is desirable to control the substrate temperature to about 25±0.5° C.
In one embodiment, the solar cell production line 200 has at least one accumulator 211 positioned after the scribe module(s) 214. During production accumulators 211C may be used to provide a ready supply of device substrates 303 to a processing module 218, and/or provide a collection area where device substrates 303 coming from the processing module 212 can be stored if the processing module 218 goes down or cannot keep up with the throughput of the scribe module(s) 214.
In one embodiment, it is generally desirable to monitor and/or actively control the temperature of the device substrates 303 exiting the accumulators 211C to assure that the results of the back contact formation step 120 are repeatable. In one aspect, it is desirable to assure that the temperature of the device substrates 303 exiting the accumulators 211C or arriving at the processing module 218 are at a temperature in a range between about 20° C. and about 26° C. In one embodiment, it is desirable to control the substrate temperature to about 25±0.5° C. In one embodiment, it is desirable to position one or more accumulators 211C that are able to retain at least about 80 device substrates 303.
Next, the device substrate 303 is transported to the processing module 218 in which one or more back contact formation steps, or step 118, are performed on the device substrate 303. In step 118, the one or more back contact formation steps 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 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 solar cell production line 200 has at least one accumulator 211 positioned after the processing module 218. During production, the accumulators 211D may be used to provide a ready supply of device substrates 303 to the scribe modules 220, and/or provide a collection area where the device substrates 303 coming from the processing module 218 can be stored if the scribe modules 220 go down or can not keep up with the throughput of the processing module 218.
In one embodiment it is generally desirable to monitor and/or actively control the temperature of the device substrates 303 exiting the accumulators 211D to assure that the results of the back contact formation step 120 are repeatable. In one aspect, it is desirable to assure that the temperature of the device substrates 303 exiting the accumulators 211D or arriving at the scribe module 220 are at a temperature in a range between about 20° C. and about 26° C. In one embodiment, it is desirable to control the substrate temperature to about 25±0.5° C. In one embodiment, it is desirable to position one or more accumulators 211C that are able to retain at least about 80 device substrates 303.
Next, the device substrate 303 is transported to the scribe module 220 in which step 120, or a back contact isolation step, is performed on the device substrate 303 to electrically isolate the individual cells disposed on the substrate surface from each other. In step 120, material is removed from the substrate surface by use of a material removal step, such as a laser ablation process. In one embodiment, an Nd:vanadate (Nd:YVO4) laser source is used ablate material from the device substrate 303 surface to form lines that electrically isolate one individual cell from the next. In one embodiment, a 5.7 m2 substrate laser scribe module, available from Applied Materials, Inc., is used to accurately scribe the desired regions of the device substrate 303. In one embodiment, the laser scribe process performed during step 120 uses a 532 nm wavelength pulsed laser to pattern the material disposed on the device substrate 303 to isolate the individual cells that make up the solar cell 300. As shown in
In one aspect, it is desirable to assure that the temperature of the device substrates 303 entering the scribe module 220 are at a temperature in a range between about 20° C. and about 26° C. by use of an active temperature control hardware assembly that may contain a resistive heater and/or chiller components (e.g., heat exchanger, thermoelectric device). In one embodiment, it is desirable to control the substrate temperature to about 25±0.5° C.
Next, the device substrate 303 is transported to the solar cell device isolation module 222 in which device isolation steps, or step 122, are performed on the device substrate 303 to separate regions of the deposited layers to form multiple smaller solar cells 300 (e.g., reference numerals 300A-330D) on the substrate 302,as shown in
In one embodiment, an Nd:vanadate (Nd:YVO4) or Nd:YAG laser source is used to ablate material from the substrate 302 surface to form regions that electrically isolate one of the smaller solar cells 300A-300D from the other. In one embodiment, the laser ablation process performed during step 122 uses a 1064 nm wavelength pulsed laser to pattern the material disposed on the substrate 302 to isolate multiple smaller solar cells 300 formed on the substrate 302 from one another as well as isolate the edges of the individual smaller solar cells 300. As shown in
In one aspect, it is desirable to assure that the temperature of the device substrates 303 entering the solar cell device isolation module 222 are at a temperature in a range between about 20° C. and about 26° C. by use of an active temperature control hardware assembly that may contain a resistive heater and/or chiller components (e.g., heat exchanger, thermoelectric device). In one embodiment, it is desirable to control the substrate temperature to about 25±0.5° C.
Next, the device substrate 303 is transported to the quality assurance module 224 in which step 124, or quality assurance and/or shunt removal steps, are performed on regions of the device substrate 303 to assure that the devices formed on the substrate surface meet a desired quality standard and, in some cases, to correct defects in the formed device. In one embodiment, the analyzed and processed regions of the device substrate 303 include each of the individual cells (e.g., individual cells 382A-382B in
If the module detects a defect in the formed device, it can take corrective actions to correct the defects in the formed smaller solar cells 300 on the device substrate 303. In one embodiment, if a short or other similar defect is found, a reverse bias may be applied between regions on the substrate surface to control and or correct one or more of the defectively formed regions of the solar cell device. During the correction process the reverse bias generally delivers a voltage high enough to cause the defects in the solar cells to be corrected. In one example, if a short is found between supposedly isolated regions of the device substrate 303 the magnitude of the reverse bias may be raised to a level that causes the conductive elements in areas between the isolated regions to change phase, decompose, or become altered in some way to eliminate or reduce the magnitude of the electrical short.
In one embodiment of the process sequence 100, the quality assurance module 224 and factory automation system are used together to resolve quality issues found in a formed device substrate 303 during the quality assurance testing. In one case, a device substrate 303 may be sent back upstream in the processing sequence to allow one or more of the fabrication steps to be re-performed on the device substrate 303 (e.g., back contact isolation step (step 120)) to correct one or more quality issues with the processed device substrate 303.
Next, the device substrate 303 is transported to the cleaning module 226 in which step 126, or a pre-lamination cleaning step, is performed on the device substrate 303 to remove any contaminants found on the surface of the multiple smaller solar cells 300 formed on the device substrate 303. Typically, the cleaning module 226 uses wet chemical scrubbing and rinsing steps to remove any undesirable contaminants found on the substrate surface. In one embodiment, a cleaning process similar to the processes described in step 106 is performed on the substrate 303 to remove any contaminants on the surface(s) of the substrate 303, such as the edge region 385, sectioning regions 386, back contact layer 350, trenches 381C, and front surface and edges of the substrate 302. In one embodiment, optical inspection or electrical conductivity tests are performed on various portions of the edge region 385 or sectioning regions 386 after step 126 to assure that all of the desired material has been removed. In one embodiment of the processing sequence 100, step 126 is performed on the device substrate 303 prior to performing step 124.
Next, the substrate 303 is transported to a bonding wire attach module 228 in which step 128, or a bonding wire attach step, is performed on the device substrate 303. Step 128 is used to attach the various wires/leads required to connect the various external electrical components to the formed smaller solar cell devices formed on the substrate 302. Typically, the bonding wire attach module 228 is an automated wire bonding tool that is used to reliably and quickly form the numerous interconnects that are often required to form the solar cells 300 formed in the production line 200. In one embodiment, the bonding wire attach module 228 is used to form the side-buss 355 (
In one embodiment, the side-buss 355 and cross-buss 356 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 each 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 356, which is electrically connected to the side-buss 355 at the junctions, can be electrically isolated from the back contact layer 350 of each of the smaller solar cells 300 by use of an insulating material 357, such as an insulating tape, as shown in
In step 130, a bonding material 360 (
Referring to
In one embodiment, the material preparation module 230A is adapted to receive the bonding material 360 in a sheet form and perform one or more cutting operations to provide a bonding material, such as Polyvinyl Butyral (PVB) or Ethylene Vinyl Acetate (EVA) that is sized to cover the surface of the substrate 302 on which the deposited layers (e.g., reference numerals 310-350) are disposed. In general, when using bonding materials 360 that are polymeric, it is desirable to control the temperature (e.g., 16-18° C.) and relative humidity (e.g., RH 20-22%) of the solar cell production line 200 where the bonding material 360 is stored and integrated into the solar cell device to assure that the attributes of the bond formed in the bonding module 232 are repeatable and the dimensions of the polymeric material are stable. It is generally desirable to store the bonding material prior to use in temperature and humidity controlled area (e.g., T=6-8° C.; RH=20-22%). The tolerance stack up of the various components in the bonded device (Step 132) can be an issue when forming large solar cells. Therefore, accurate control of the bonding material properties and tolerances of the cutting process are required to assure that a reliable hermetic seal is formed. In one embodiment, PVB may be used to advantage due to its UV stability, moisture resistance, thermal cycling, good US fire rating, compliance with International Building Code, low cost, and reworkable thermo-plastic properties.
In one part of step 130, the bonding material 360 is transported and positioned over the back contact layer 350, the side-buss 355 (
In one embodiment, prior to positioning the back glass substrate 361 over the bonding material 360, one or more preparation steps are performed on the back glass substrate 361 to assure that subsequent sealing processes and final solar product are desirably formed. In one case, the back glass substrate 361 is received in a “raw” state where the edges, overall size, and/or cleanliness of the substrate 361 are not well controlled. Receiving “raw” substrates reduces the cost to prepare and store substrates 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. In one embodiment of step 130, the back glass substrate 361 surfaces and edges are prepared in a seaming module (e.g., front end seaming module 204) prior to performing the back glass substrate cleaning step. In the next sub-step of step 132, the back glass substrate 361 is transported to the glass cleaning module 230C in which a substrate cleaning step is performed on the substrate 361 to remove any contaminants on the surface of the substrate 361. Common contaminants may include materials deposited on the substrate 361 during the substrate forming process (e.g., glass manufacturing process) and/or during shipping of the substrates 361. Typically, the glass cleaning module 230C uses wet chemical scrubbing and rinsing steps to remove any undesirable contaminants as discussed above. The prepared back glass substrate 361 is then positioned over the bonding material 360 and the device substrate 303 by use of an automated robotic device.
Next, the device substrate 303, the back glass substrate 361, and the bonding material 360 are transported to the bonding module 232 in which lamination steps, or step 132, are performed to bond the back glass substrate 361 to the device substrate 303 formed in steps 102-130 discussed above. In step 132, the bonding material 360, such as Polyvinyl Butyral (PVB) or Ethylene Vinyl Acetate (EVA), is sandwiched between the back glass substrate 361 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 232.
The device substrate 303, the back glass substrate 361, and bonding material 360 thus form a composite solar cell structure 304 (
Next, the composite solar cell structure 304 is transported to the autoclave module 234 in which step 134, or autoclave steps are performed on the composite solar cell structure 304 to remove trapped gasses in the bonded structure and assure that a good bond is formed. In step 134, a composite solar cell structure 304 is inserted into the processing region of the autoclave module 234, 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 361, and the bonding material 360. The processes performed in the autoclave module 234 are also useful to assure that the stress in the glass and bonding layer (e.g., PVB layer) are controlled to prevent future failures of the hermetic seal or failure of the glass due to the stress induced during the bonding/lamination processes. In one embodiment, it may be desirable to heat the device substrate 303, back glass substrate 361, and bonding material 360 to a temperature that causes stress relaxation in one or more of the components in the composite solar cell structure 304.
Next, the composite solar cell structure 304 is transported to the junction box attachment module 236 in which junction box attachment steps 136 are performed on the composite solar cell structure 304. The junction box attachment module 236, used during step 136, is used to install a junction box 370 (
Next, the composite solar cell structure 304 is transported to the device testing module 238 in which device screening and analysis steps 138 are performed on the composite solar cell structure 304 to assure that the devices formed in the composite solar cell structure 304 meet desired quality standards. In one embodiment, the device testing module 238 is a solar simulator module that is used to qualify and test the output of the one or more formed smaller solar cells 300. In step 138, a light emitting source and probing device are used to measure the output of the formed smaller solar cells 300 by use of one or more automated components that are adapted to make electrical contact with terminals in the junction box 370. If the module detects a defect in the formed device, it can take corrective actions or the particular smaller solar cell 300 can be scrapped once sectioned from the other formed smaller solar cells in subsequent steps (i.e., step 140).
Next, the composite solar cell structure 304 is optionally transported to the sectioning module 240 in which a sectioning step 140 is used to section the composite solar cell structure 304 into a plurality of smaller solar cells 300 to form a plurality of smaller solar cell devices. In one embodiment, the composite solar cell structure 304 is sectioned along reference lines X-X and Y-Y, as shown in
In one embodiment, the solar cell production line 200 is adapted to accept (step 102) and process substrate 302 or device substrates 303 that are 5.7 m2 or larger. In one embodiment, these large area substrates 302 are fully processed and then sectioned into four 1.4 m2 device substrates 303 during step 142. In one embodiment, the system is designed to process large device substrates 303 (e.g., TCO coated 2200 mm×2600 mm×3 mm glass) and produce various sized solar cell devices without additional equipment or processing steps. Currently amorphous silicon (a-Si) thin film factories must have one product line for each different size solar cell device. In the present invention, the production line 200 is able to manufacture different solar cell device sizes with minimal or no conversion time. In one aspect of the invention, the manufacturing line is able to provide a high solar cell device throughput, which is typically measured in Mega-Watts per year, by forming solar cell devices on a single large substrate and then sectioning the substrate to form solar cells of a more preferable smaller size.
This flexibility in output with a single input is unique in the solar thin film industry and offers significant savings in capital expenditure and reduction in processing complexity. The material cost for the input glass is also lower since solar cell device manufacturers can purchase a larger quantity of a single glass size to produce the various size solar cell devices. A more detailed description of exemplary sectioning modules 240 are presented below in the section entitled, “Sectioning Module and Processes.”
Next, each composite solar cell structure 304 is optionally transported to a back end seaming module 242 in which a seaming step 142 is used to prepare the edges of each composite solar cell structure 304 to reduce the likelihood of damage, such as chipping or crack initiation from the edge of the composite solar cell structure 304. In one embodiment, the back end seaming module 242 is used to round or bevel the edges of each composite solar cell structure 304. In one embodiment, a diamond impregnated belt or disc is used to grind the material from the edges of the composite solar cell structure 304. In another embodiment, a grinding wheel, grit blasting, or laser ablation technique is used to remove the material from the edges of the composite solar cell structure 304.
Next, each composite solar cell structure 304 is transported to the support structure module 244 in which support structure mounting steps 144 are performed on each composite solar cell structure 304 to provide a complete solar cell device that has one or more mounting elements attached to the composite solar cell structure 304 formed using steps 102-142 to a complete solar cell device that can easily be mounted and rapidly installed at a customer's site.
Next, the composite solar cell structure 304 is transported to the unload module 246 in which step 146, or device unload steps are performed to remove the formed smaller solar cells 300 from the solar cell production line 200.
In one embodiment of the solar cell production line 200, one or more regions in the production line are positioned in a clean room environment to reduce or prevent contamination from affecting the solar cell device yield and useable lifetime. In one embodiment, as shown in
The sectioning module 240 and processing sequence performed during the sectioning step 140 are used to section a large processed and tested composite solar cell structure 304 into two or more smaller composite solar cell structures 304, each containing a smaller solar cell 300. In one embodiment, the sectioning module 240 receives a 2600 mm×2200 mm composite solar cell structure 304 and sections it into two 1300 mm×2200 mm processed and tested composite solar cell structures 304. In one embodiment, the sectioning module 240 receives a 2600 mm×2200 mm composite solar cell structure 304 and sections it into two 2600 mm×1100 mm processed and tested composite solar cell structures 304. In one embodiment, the sectioning module 240 receives a 2600 mm×2200 mm composite solar cell structure 304 and sections it into four 1300 mm×1100 mm processed and tested composite solar cell structures 304.
In one embodiment, the system controller 290 (
In one embodiment, the scoring mechanism 424 is a mechanical scoring mechanism, such as a mechanical scoring wheel. In one embodiment, the scoring mechanism 424 is an optical scoring mechanism, such a laser scoring mechanism.
The scored composite solar cell structure 304 is then transported via the scoring station conveyor 422 partially onto a cross transfer station 430 as shown in
In one embodiment, the rollers 426 and 427 are padded cylindrical rollers extending the length of the composite solar cell structure 304. The roller 426 is raised by an actuator 428, and the roller 427 is lowered by an actuator 429. In one embodiment, the actuator 428 and the actuator 429 may each be an electric, hydraulic, or pneumatic motor. In one embodiment, the actuator 428 and the actuator 429 may each be a hydraulic or pneumatic cylinder. In one embodiment, the actuator 428 and the actuator 429 are each controlled and coordinated by the system controller 290.
Next, shown in
In one embodiment, rather than the above described break operations, the composite solar cell structure 304 is sectioned via a laser cutting process.
In one embodiment, after performing each of the above described break operations, it is further desirable to cut the bonding material 360 disposed between the glass substrate 302 and back glass substrate 361 to assure that the sectioned smaller solar cells 300 can be physically separated. In one embodiment, the process of cutting the bonding material 360 is performed in the sectioning module 240 by use of a cutting device (not shown), such as a knife, saw, cutting wheel, laser, or other similar device. In one embodiment, an additional step of cutting the bonding material 360 is performed after all of the breaking operations are performed. In another embodiment, the substrate cutting process is performed after each interim break operation step, such as after the first break operation shown in
Although the above-described embodiment illustrates processes and apparatus for sectioning a single composite solar cell structure 304 into four smaller sections, it should be evident that the embodiment works equally well for sectioning a single composite solar cell structure 304 into two smaller sections by adjusting the scoring mechanism 424 to score only a single line on either the X-axis or the Y-axis and performing only a single break or cut process.
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.
This application is related to U.S. application Ser. No. 12/202,199, filed Aug. 29, 2008 (Attorney Docket No. APPM/11141) and U.S. application Ser. No. 12/201,840, filed Aug. 29, 2008 (Attorney Docket No. APPM/11141.02), each of which is incorporated by reference herein.
