Patent Application
20110053307
1. Field of the Invention
Embodiments of the present invention generally relate to a method of forming solar cell devices. In particular, embodiments of the invention relate to methods of processing encapsulant layers of a solar cell device and forming solar cell devices using processed encapsulant layers.
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.
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 backside 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 high overall performance.
With traditional energy source prices on the rise, there is a need for a low-cost way 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, a major challenge in encapsulation of large-sized solar cells is achieving bubble-free lamination results across locally stepped topography, such as from internal electrical connections, e.g., cross- and side-buss ribbons that collect power from individual solar cells on the front glass. The large size (2.2 m×2.6 m) of substrates and the cross- and side-buss wires on the glass make the lamination process particularly sensitive to bubble formation. Bubble formation during lamination may create paths from edge to center, causing delamination or environmental encroachment, such as rain, to seep into the area and damage the solar cell.
One method to prevent bubble formation is patterning the back glass to decrease air entrapment between the encapsulant material and the back glass. Chemical etchants may be used to pattern the back glass. However, patterning the glass tends to weaken the glass substrate. Another method to prevent bubble formation is to machine encapsulant material to form a pattern. The machining process typically uses a mill to cut the pattern in the encapsulant. However, machining encapsulant tends to be expensive, very difficult, and creates a gummy final product. Therefore, there is a need for a method of decreasing bubble formation during lamination of large-size substrates used in the manufacture of solar cells along a production line having a suite of modules and improve solar cell quality.
In one embodiment, a method of forming a composite solar cell structure includes preparing a device substrate, wherein the device substrate includes a glass substrate, a transparent conductive layer deposited over the glass substrate, one or more silicon layers deposited over the transparent conductive layer, a back contact layer deposited over the one or more silicon layers, and one or more internal electrical connections disposed on the back contact layer. The method also includes forming a mating pattern on a bonding material to match a topography of an exposed surface of the device substrate, the exposed surface comprising the back contact layer and the one or more internal electrical connections. The method also includes positioning the bonding material over the exposed surface, disposing a back glass substrate over the bonding material to form a composite structure, and compressing the composite structure.
In another embodiment, a method of preparing a pre-patterned bonding material for a solar cell assembly includes placing a bonding material over a work surface having an embossment, wherein at least a portion of the embossment corresponds to a topography of an exposed surface of a device substrate, heating the bonding material, and pressing the bonding material onto the embossment to form a mating pattern.
In another embodiment, a method of preparing a pre-patterned bonding material for a solar cell assembly, includes passing a bonding material between at least two rollers, wherein at least one roller has an embossment, at least a portion of the embossment corresponding to a topography of an exposed surface of a device substrate, heating the bonding material, and pressing the bonding material onto the embossment to form a mating pattern as the bonding material passes through the two rollers.
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 invention provide a method of pre-patterning a bonding material to match a topography of an exposed surface of the device substrate. In one embodiment, the bonding material is pre-patterned before use in the formation of a solar cell by embossing a pattern that matches the topography of an exposed surface comprising a back contact layer and one or more internal electrical connections. In one embodiment, the bonding material is pressed on a work surface having an embossment that corresponds to the topography of the exposed surface. In one embodiment, the bonding material is passed between at least two rollers where at least one roller has an embossment that corresponds to the topography of the exposed surface. In one embodiment of the present invention, a method for forming a composite solar cell structure is provided.
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, such as about 5.7 m2, and performing multiple deposition, material removal, cleaning, sectioning, bonding, and various inspection and testing 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.
While the discussion below primarily describes the formation of thin-film solar cell devices, this configuration is not intended to be limiting as to 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 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. 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
As shown in
The solar cell 300 further comprises a first transparent conducting oxide (TCO) layer 310 (e.g., zinc oxide (ZnO), tin oxide (SnO)) formed over the substrate 302, a first p-i-n junction 320 formed over the first TCO layer 310, a second TCO layer 340 formed over the first p-i-n junction 320, and a back contact layer 350 formed over the second TCO layer 340. 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 amorphous 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 amorphous silicon layer 326 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 the group consisting of Al, Ag, Ti, Cr, Au, Cu, Pt, alloys thereof, and combinations thereof.
In the embodiment shown in
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 the group consisting of Al, Ag, Ti, Cr, Au, Cu, Pt, alloys thereof, and combinations thereof.
As shown in
Three laser scribing steps may be performed to produce trenches 381A, 381B, and 381C, which are generally required to form a high-efficiency solar cell device. Although formed together on the substrate 302, the individual cells 382A and 382B are isolated from each other by the insulating trench 381C formed in the back contact layer 350 and the first p-i-n junction 320. In addition, the trench 381B is formed in the first p-i-n junction 320 so that the back contact layer 350 is in electrical contact with the first TCO layer 310.
In one embodiment, the insulating trench 381A is formed by the laser scribe removal of a portion of the first TCO layer 310 prior to the deposition of the first p-i-n junction 320 and the back contact layer 350. Similarly, in one embodiment, the trench 381B is formed in the first p-i-n junction 320 by the laser scribe removal of a portion of the first p-i-n junction 320 prior to the deposition of the back contact layer 350. While a single-junction-type solar cell is illustrated 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. In the next step, 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 substrate 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.
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 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 205 uses wet chemical scrubbing and rinsing steps to remove any undesirable contaminants.
In the next step, or step 108, separate cells are electrically isolated from one another via scribing processes. Contamination particles on the TCO surface and/or on the bare glass surface can interfere with the scribing procedure. In one embodiment, the cleaning module 205 is available from the Energy and Environment Solutions division of Applied Materials, Inc. of 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.
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 cell isolation 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 105 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 the 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. 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 in the solar cell device formed 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.
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 216 in which step 114, or the interconnect formation step, 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. As shown in
Next, the device substrate 303 is transported to the processing module 218 in which one or more substrate back contact formation steps, or step 118, are performed on the device substrate 303. In step 118, the one or more substrate 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 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 ATONTM PVD 5.7 tool available from Applied Materials, Inc. of 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 substrates to the scribe modules 220, and/or provide a collection area where substrates coming from the processing module 218 can be stored if the scribe modules 220 go down or cannot keep up with the throughput of the processing module 218.
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 plurality of solar cells contained 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. As shown in
Next, the device substrate 303 is optionally transported to the substrate sectioning module 224 in which a substrate sectioning step 124 is used to cut the device substrate 303 into a plurality of smaller device substrates 303 to form a plurality of smaller solar cell devices.
Referring back to
Next, the device substrate 303 is transported to the pre-screen module 228 in which optional pre-screen steps 128 are performed on the device substrate 303 to assure that the devices formed on the substrate surface meet a desired quality standard. Next, the device substrate 303 is transported to the cleaning module 230 in which step 130, or a pre-lamination substrate cleaning step, is performed on the device substrate 303 to remove any contaminants found on the surface of the substrates 303 after performing steps 122-127.
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 355 (
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(s) of the solar cell by use of an insulating material 357, such as an insulating tape. The ends of each of the cross-busses 356 generally have one or more leads that are used to connect the side-buss 355 and the cross-buss 356 to the electrical connections found in a junction box 370, which is used to connect the formed solar cell to the other external electrical components.
In the next step, step 132, a bonding material 360 (
Referring to
In one embodiment, the material preparation module 232A 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 form a reliable seal between the back glass substrate 361 and the solar cells formed on the device substrate 303. 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 234 (discussed below) are repeatable and the dimensions of the polymeric material is stable. It is generally desirable to store the bonding material prior to use in a 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 134) 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 example, a 30-gauge or a 45-gauge PVB material sheet is used to bond the back glass substrate 361 to the device substrate 303. In one part of step 132, the bonding material is transported and positioned over the back contact layer 350 and side-buss 355 (
In the next sub-step of step 132, the back glass substrate 361 is transported to the cleaning module 232C in which a substrate cleaning step is performed on the substrate 361 to remove any contaminants found on the surface of the substrate 361. The prepared back glass substrate 361 is then positioned over the bonding material and 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 234 in which step 134, or lamination steps, are performed to bond the backside glass substrate to the solar cell devices formed in steps 102-130 discussed above. In step 134, a bonding material 360, such as Polyvinyl Butyral (PVB) or Ethylene Vinyl Acetate (EVA), is sandwiched between the backside glass substrate 361 and the solar cells, and heat and pressure is applied to the structure to form a bonded and sealed device using various heating elements and other devices found in the bonding module 234, which are discussed below. 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 236 in which step 136, or autoclave steps are performed on the composite structure to remove trapped gases in the bonded structure and assure that a good bond is formed during step 134. In step 134, a bonded structure 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 substrate 302, back glass substrate, and bonding material 360. 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 substrate, back glass substrate 361, and bonding material 360 to a temperature that causes stress relaxation in the one or more of the components formed in the composite 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 370 (
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.
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'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 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
Referring to
As noted above, during step 134, or the lamination step, one or more process steps are performed to bond the backside glass substrate to the solar cell devices formed in steps 102-132 to form a bonded composite solar cell structure 304 (
The preheat module 411 generally contains a plurality of support rollers 421, a plurality of heating elements 401A, 401B, two or more temperature sensors (e.g., temperature sensors 402A, 402B), and one or more compression rollers 431A. The plurality of support rollers 421 are adapted to support the composite solar cell structure 304 while it is positioned within the processing region 415 of the preheat module 411 and are configured to withstand the temperatures created by the heating elements 401A, 401B during normal processing. In one embodiment, the preheat module 411 also contains a fluid delivery system 440A that is use to deliver a desired flow of a fluid, such as air or nitrogen (N2), through the processing region 415 during processing.
The plurality of heating elements 401A, 401B are typically lamps (e.g., IR lamps), resistive heating elements, or other heat generating devices that are controlled by the system controller 290 to deliver a desired amount of heat to desired regions of the composite solar cell structure 304 during processing. In one embodiment, a plurality of heating elements 401A are positioned above the composite solar cell structure 304, and a plurality of heating elements 401B are positioned below the composite solar cell structure 304. In one embodiment, the heating elements 401A, 401B are oriented substantially perpendicular to the direction of travel of the substrate, and the energy delivered by the lamps creates a uniform temperature profile across the substrate as it is continually moved through the processing region 415.
The compression rollers 431A are adapted to provide a desired amount of force F to the composite solar cell structure 304 to help remove the air bubbles found within the composite solar cell structure 304 and evenly distribute the bonding material within the composite solar cell structure 304 after performing the preheat process step. The compression rollers 431A are generally configured to receive the composite solar cell structure 304 after it has been sufficiently heated in the preheat module 411.
Referring to
In general, during the preheat process the composite solar cell structure 304 is controllably heated as it passes through the processing region 415 by use of the one more of the heating elements 401A, 401B disposed therein. In one embodiment, at least one of the top heating elements 401A and at least one of the bottom heating elements 401B are close loop controlled using the system controller 290 and at least one temperature sensor 402B positioned on the top of the substrate and at least one temperature sensor 402B positioned on the bottom of the substrate. After the substrate is preheated, a desired force is applied to one or more sides of the preheated substrate by use of the one or more compression rollers 431A using one or more controlled force generating elements. The applied force supplied by the one or more compression rollers 431A may be between about 200 [N/cm] and about 600 [N/cm].
The lamination module 410 generally contains a plurality of support rollers 421, a plurality of heating elements 401C, 401D, two or more temperature sensors (e.g., temperature sensors 402C, 402D), and one or more compression rollers 431B. The plurality of support rollers 421 are adapted to support the composite solar cell structure 304 while it is positioned within the processing region 416 of the lamination module 410 and are configured to withstand the temperatures achieved during normal thermal processing. In one embodiment, the lamination module 410 also contains a fluid delivery system 440B that is used to deliver a desired flow of a fluid through the processing region 416 during processing. In one embodiment, the fluid delivery system 440B is a fan assembly that is adapted to deliver a desired flow of air across one or more surfaces of the substrate disposed within the processing region 416 by use of commands sent from the system controller 290.
The plurality of heating elements 401C, 401D are typically lamps (e.g., IR lamps), resistive heating elements, or other heat-generating devices that are controlled by the system controller 290 to deliver a desired amount of heat to desired regions of the composite solar cell structure 304 during processing. In one embodiment, a plurality of heating elements 401C are positioned above the composite solar cell structure 304, and a plurality of heating elements 401D are positioned below the composite solar cell structure 304. In one embodiment, the heating elements 401C, 401D are oriented substantially perpendicular to the direction of travel of the substrate, and the energy delivered by the lamps creates a uniform temperature profile across the substrate as it is moved through the processing region.
The one or more compression rollers 431B are adapted to provide a desired amount of force F to the composite solar cell structure 304 (i.e., composite structure) to help remove the air bubbles found within the composite solar cell structure 304 and evenly distribute the bonding material within the composite solar cell structure 304. The compression rollers 431B are generally configured to receive the composite solar cell structure 304 after it has been sufficiently heated in the lamination module 410. In one embodiment, as shown in
Referring to
Therefore, after performing the preheat process, a lamination process is performed in the lamination module 410. During the lamination process, the composite solar cell structure 304 is controllably heated as it passes through the processing region 416 by use of the one more of the heating elements 401C, 401D disposed therein. In one embodiment, at least one of the top heating elements 401C and at least one of the bottom heating elements 401D are close loop controlled, using the system controller 290 and at least one temperature sensor 402C positioned on the top of the substrate and at least one temperature sensor 402D positioned on the bottom of the substrate. After the substrate is heated in the lamination module, a desired force is applied to one or more sides of the composite substrate by use of the one or more compression rollers 431B, using one or more controlled force generating elements. The applied force supplied by the one or more compression rollers 431B may be between about 200 [N/cm] and about 600 [N/cm].
As discussed above, in step 134, the composite solar cell structure is inserted in the processing region of the autoclave module, where heat and pressure is applied to the partially formed solar cells to reduce the amount of trapped gas disposed between bonding material 360 and the back glass substrate 361, substrate 302 or the back contact layer 350 to prevent environmental attack of portions of the solar cell device through the regions of trapped gas. Use of the autoclave process is also used to improve the properties of the bond between the substrate 302, back glass substrate and bonding material 360. 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.
To control the temperature of the composite solar cell structures 304 during the autoclave process, the system controller 290 and temperature sensor “T” are used in combination to control the amount of heat that is transferred to the composite solar cell structures 304 positioned in the processing region 517 by use of the components contained in the heating unit 513 and the cooling unit 514. The heating unit 513 generally contains a heater controller 513A and a plurality of heating elements 513B (e.g., thermally-controlled resistance heating elements) that are in thermal communication with the composite solar cell structures 304 disposed within the processing region 517. Similarly, the cooling unit 514 contains a cooling unit controller 514A and a plurality of cooling elements 514B that are in thermal communication with the composite solar cell structures 304 disposed within the processing region 517. The cooling elements 514B may comprise a series of fluid-containing channels, in which a fluid exchanging medium is provided from the cooling unit controller 514A, to cool the components contained in the processing region 517. In one example, the heating elements 513B and/or cooling elements 514B are disposed within the processing region 517 and are adapted to add and/or remove heat from the composite solar cell structures 304 by convective heat transfer supplied by movement of the high-pressure gas contained in the processing region 517 during processing by use of the fluid movement device 511 (e.g., mechanical fan). The fluid movement device 511 is configured to provide motion to the fluid contained in the processing region 517 during processing to also reduce the variation in temperature throughout the processing region 517. In one embodiment, the temperature in the processing region is maintained between about 140° C. and about 160° C. for a time between about 1 and about 4 hours. The autoclave processing temperatures, pressures, and times will vary by the type of bonding material that is used, and as one or more of the process variables are altered.
The loading system 530 is generally configured to deliver and remove one or more of the racks 520 to the processing region 517 of the vessel 515 prior to and after processing. The loading system 530 generally contains an automated material handling device 531, for example, a conveyor or a robotic device, which is used to transfer the racks 520 to and from the processing region 517 of the vessel 515 in an automated fashion.
The one or more substrate racks 520 generally include one or more regions of shelves 521 that are adapted to support the composite solar cell structures 304 during processing. In one embodiment, each substrate rack 520 contains wheels 521A that allows the racks to be easily moved and positioned within the production line 200. Each of the composite solar cell structures 304 are spaced a desired distance apart to assure that temperature uniformity and pressures applied to the composite solar cell structures 304 are uniform. In one embodiment, to assure that the substrates see the same processing conditions, one or more spacers 522 are disposed between and in contact with both adjacent composite solar cell structures 304 to assure that the spacing between the adjacent composite solar cell structures 304 is uniform. In one embodiment, three or more spacers are positioned between adjacent composite solar cell structures 304. In one example, the spacers 522 are adapted to space adjacent composite solar cell structures 304 between about 5 mm and about 15 mm apart.
In general, the autoclave module 236 may be transferrably connected to the automation device 281, positioned after the bonding module 234, to receive and perform an autoclave process on one or more of the formed composite solar cell structures 304. The autoclave module 236 may also be transferrably connected to the automation device 281 positioned before the junction box attachment module 238 so that the processed substrates can be transferred to the down stream processing modules.
In one embodiment, as shown in
As previously set forth, steps 131-136 of the processing sequence 100 may be used to form a composite solar cell structure 304 from the device substrate 303 using the bonding wire attach module 231, the bonding module 234, and the autoclave module 236.
Next, a bonding material 360 and backing glass substrate 361 are laminated together, forming a composite solar cell structure 304. As can be seen from the cross-sectional side view of
A central hole 815 corresponds to a hole in the back substrate glass 361 and bonding material 360 necessary to electrically connect the junction box with the cross-buss 356, as previously described in step 138. The bonding material may be pre-cut into sheets that match the size of the device substrate 303. Pre-cutting the bonding material may take place at material perpetration module 232A discussed above in connection with process steps 131-136.
After the bonding material 360 is placed on the work surface, the bonding material 360 is heated and then pressed onto the embossment 808 to form a mating pattern. The heating of the bonding material may include locally heating a portion of the bonding material corresponding to the topography of the exposed surface. In one embodiment, only the embossment 808 is heated to create the localized heating of the bonding material 360 along the areas of the mating pattern. Localized heating may be useful because heating up the entire bonding material 360 may cause shrinkage and negatively impact the ability of the bonding material 360 to sufficiently cover the exposed surface of the device substrate 303. The localized heating may heat portions of the bonding material to a temperature between 30 and 95° C. for imprinting the pattern on the bonding material.
In one embodiment a platen may be pressed down on the bonding material, creating a die to form the mating pattern. In other embodiments a roller may roll across the work surface to imprint the mating pattern on the bonding material 360. Additionally, various pressures may be used to press the bonding material 360 on the embossment 808 to form the mating pattern. The pressure and time of embossing are interrelated and can be adjusted to provide the desired mating pattern without negatively affecting the physical and chemical properties of the bonding material 360. Any of these disclosed methods of pre-patterning the bonding material 360 may be performed at material perpetration module 232A discussed above in connection with process steps 131-136.
A plurality of holes 805 may be used to inject air from the bottom of the work surface 800 to prevent sticking of the bonding layer 360 after embossing the mating pattern. The bonding material may easily stick to various surfaces, and injecting air through holes 805 can be used to remove the bonding material 360 from the work surface 800. In another embodiment, the embossment 808 and work surface 800 may have a coating that prevents sticking. These stick-prevention features may be particularly desirable for PVB, which tends to stick very well, especially when heated. Furthermore, local heating around the area so embossed will help minimize the overall heating instability of the bonding material 360, such as PVB.
In other embodiments of the invention, pre- and post-processing steps may be performed. One type of pre-processing step would be relaxing the bonding material 360 before placing the bonding material 360 over the work surface 800. Relaxing the bonding material, such as PVB, may help the PVB layer to flow when it passes though the rollers in the lamination step previously discussed, further helping to prevent bubble formation. Relaxing the bonding material may also prevent the edges from pulling away from the glass substrate during lamination and further increasing the chance of atmospheric contamination. Additionally, relaxed bonding material may not move as much, preventing inadvertent movement of the cross- and side-busses during lamination. Bonding material that moves too much may push and fight against the busses and increase the chance for bubble formation.
Relaxing the bonding material may be performed in two steps, a heating step, and a quick cooling step. One type of post-processing step may be chilling the bonding material 360 after pressing the bonding material 360 onto the embossment 808. Chilling also helps to prevent the edge problems. The bonding material may be chilled after embossment to between 18 and 25° C. Combined pre- and post-processing improves the physical characteristics of the bonding material and increases the likelihood of bubble prevention during lamination.
Once the bonding material has been embossed, the will need to know the orientation of the glass and bonding material so that the mating pattern formed in the bonding material will properly align, angularly and axially, with the device substrate 303. An automated vision system may match the bonding material 360 with the back glass substrate 361 prior to lamination.
The embossment 908 may have the same pattern as the busses 355, 356. For example, the embossment 908 includes a side-buss surface projection 910 corresponding in length and thickness to the side-buss 355. A cross-buss surface projection 912 roughly mirrors the length and thickness of the cross-buss 356. A central hole 915 corresponds to a hole in the back substrate glass 361 and bonding material 360 necessary to electrically connect the junction box with the cross-buss 356, as previously described in step 138. The bonding material may be pre-cut into sheets that match the size of the device substrate 303. Pre-cutting the bonding material may take place at material perpetration module 232A discussed above in connection with process steps 131-136.
The bonding material 360 is heated and passed through the rollers 900 to form a mating pattern. The heating of the bonding material may include locally heating the rollers or a portion of the bonding material corresponding to the topography of the exposed surface. In one embodiment, only the embossment 908 is heated to create the localized heating of the bonding material 360 along the areas of the mating pattern. The localized heating may heat portions of the bonding material to a temperature between 30 and 95° C. for imprinting the pattern on the bonding material.
Similar pre- and post-pattern processing steps may be performed to prepare the bonding material for lamination. In one embodiment, the bonding material 360 may continuously roll off a reel of the bonding material and pass between the rollers 900. In this method, the bonding material would not need to be pre-cut, but could come of another reel and cut to size just before placement over the exposed surface of the cross- and side-busses and the back contact layer prior to lamination. A separate embossment table or work surface would be unnecessary.
The above described embodiments can be readily implemented along an automated solar cell production line and help prevent bubble formation during lamination of large area solar cell substrates. Prevention of bubble formation improves efficiency due to decreased exposure to environmental conditions, such as heat and humidity. Large-sized solar cells present a challenge due to the locally stepped topography from cross- and side-busses, which embodiments of the invention help overcome.
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 claims benefit of U.S. Provisional Patent Application Ser. No. 61/239,376 (APPM/014180L), filed Sep. 2, 2009, which is herein incorporated by reference. This application is related to U.S. application Ser. No. 12/202,199, filed Aug. 29, 2008 (Attorney Docket No. APPM/11141), U.S. application Ser. No. 12/201,840, filed Aug. 29, 2008 (Attorney Docket No. APPM/11141.02), and U.S. Provisional Application Ser. No. 61/149,942, filed Feb. 4, 2009 (Attorney Docket No. APPM/13847L).
| Number | Date | Country | |
|---|---|---|---|
| 61239376 | Sep 2009 | US |
