Patent Application
20110139073
The subject matter disclosed herein relates generally to the field of thin film deposition systems wherein a thin film layer, such as a semiconductor material layer, is deposited on a substrate conveyed through the system. More particularly, the subject matter is related to a conveyor unit for use in a vapor deposition apparatus that is particularly suited for depositing a thin film layer of a photo-reactive material on a glass substrate in the formation of photovoltaic (PV) modules.
Thin film photovoltaic (PV) modules (also referred to as “solar panels”) based on cadmium telluride (CdTe) paired with cadmium sulfide (CdS) as the photo-reactive components are gaining wide acceptance and interest in the industry. CdTe is a semiconductor material having characteristics particularly suited for conversion of solar energy (sunlight) to electricity. For example, CdTe has an energy bandgap of 1.45 eV, which enables it to convert more energy from the solar spectrum as compared to lower bandgap (1.1 eV) semiconductor materials historically used in solar cell applications. Also, CdTe converts energy in lower or diffuse light conditions as compared to the lower bandgap materials and, thus, has a longer effective conversion time over the course of a day or in low-light (e.g., cloudy) conditions as compared to other conventional materials.
Solar energy systems using CdTe PV modules are generally recognized as the most cost efficient of the commercially available systems in terms of cost per watt of power generated. However, the advantages of CdTe not withstanding, sustainable commercial exploitation and acceptance of solar power as a supplemental or primary source of industrial or residential power depends on the ability to produce efficient PV modules on a large scale and in a cost effective manlier.
Certain factors greatly affect the efficiency of CdTe PV modules in terms of cost and power generation capacity. For example, CdTe is relatively expensive and, thus, efficient utilization (i.e., minimal waste) of the material is a primary cost factor. In addition, the energy conversion efficiency of the module is a factor of certain characteristics of the deposited CdTe film layer. Non-uniformity or defects in the film layer can significantly decrease the output of the module, thereby adding to the cost per unit of power. In addition, the ability to process relatively large substrates on an economically sensible commercial scale is a crucial consideration.
CSS (Close Space Sublimation) is a known commercial vapor deposition process for production of CdTe modules. Reference is made, for example, to U.S. Pat. No. 6,444,043 and U.S. Pat. No. 6,423,565. Within the vapor deposition chamber in a CSS process, the substrate is brought to an opposed position at a relatively small distance (i.e., about 2-3 mm) opposite to a CdTe source. The CdTe material sublimes and deposits onto the surface of the substrate. In the CSS system of U.S. Pat. No. 6,444,043 cited above, the CdTe material is in granular form and is held in a heated receptacle within the vapor deposition chamber. The sublimated material moves through holes in a cover placed over the receptacle and deposits onto the stationary glass surface, which is held at the smallest possible distance (1-2 mm) above the cover frame. The cover is heated to a temperature greater than the receptacle.
While there are advantages to known CSS processes, the systems are inherently a batch process wherein the glass substrate is indexed into a vapor deposition chamber, held in the chamber for a finite period of time in which the film layer is formed, and subsequently indexed out of the chamber. The system is more suited for batch processing of relatively small surface area substrates. The process must be periodically interrupted in order to replenish the CdTe source, which is detrimental to a large scale production process. In addition, the deposition process cannot readily be stopped and restarted in a controlled manner, resulting in significant non-utilization (i.e., waste) of the CdTe material during the indexing of the substrates into and out of the chamber, and during any steps needed to position the substrate within the chamber.
Accordingly, there exists an ongoing need in the industry for an improved vapor depositon apparatus for economically feasible large scale production of efficient PV modules, particularly CdTe modules. The present invention relates to a conveyor unit that serves this purpose.
Aspects and advantages of the invention will be set forth in part in the following description, or may be obvious from the description, or may be learned through practice of the invention.
In accordance with an embodiment of the invention, a conveyor assembly is provided that is particularly suited for use in a vapor deposition apparatus wherein a sublimated source material, such as CdTe, is deposited as a thin film layer on a photovoltaic (PV) module substrate. The conveyor assembly includes a housing that defines an enclosed interior volume. A conveyor is operably disposed within the housing and is driven in an endless loop path within the housing, for example between opposite sprockets, with at least one of the sprockets being a drive sprocket. The endless loop path of the conveyor includes an upper leg that moves in a conveyance direction of the substrates through the assembly, and a lower leg that moves in an opposite return direction. The housing includes a top member that defines an open vapor deposition area wherein the conveyor (and thus a substrate carried on the conveyor) is exposed to sublimated source material as the conveyor moves along the upper leg of the endless loop path. In a particular embodiment, the conveyor is formed from a plurality of interconnected slats, with each slat having a respective flat, planar, outer surface and transverse edge profiles such that, along at least the upper leg of the endless loop path, the outer surfaces of the slats lie in a common horizontal plane and define an uninterrupted flat support surface for a substrate conveyed through the assembly.
Variations and modifications to the embodiment of the conveyor assembly discussed above are within the scope and spirit of the invention and may be further described herein.
The present invention also encompasses a vapor deposition module that incorporates a conveyor assembly in accordance with aspects of the invention. For example, the invention provides a vapor deposition module for deposition of a sublimated source material, such as CdTe, as a thin film on a photovoltaic (PV) module substrate that is conveyed through the vapor deposition module. The module includes a casing, and a vapor deposition head operably configured within the casing to sublimate a source material. A conveyor assembly is operably configured within the casing below the vapor deposition head, and includes a housing that defines an enclosed interior volume. A conveyor is operably disposed within the housing and is drivable in an endless loop path within the housing. The endless loop path has an upper leg that moves in a conveyance direction of a substrate through the module, and a lower leg that moves in an opposite return direction. The housing further includes a top member that defines an open deposition area wherein the conveyor (and thus the upper surface of a substrate supported on the conveyor) is exposed to the vapor deposition head as the conveyor moves along the upper leg of the endless loop path.
The conveyor may include a plurality of interconnected slats, with each slat having a respective flat, planar, outer surface and transverse edge profiles such that, along the upper leg of the endless loop path, the outer surfaces of the slats lie in a common horizontal plane and define an uninterrupted flat support surface for a substrate conveyed through the module. The vapor deposition head is configured on the conveyor assembly housing such that sublimated source material from the vapor deposition head is directed to the open deposition area and onto the upper surface of a substrate supported by the conveyor.
Variations and modifications to the embodiment of the vapor deposition module discussed above are within the scope and spirit of the invention and may be further described herein.
These and other features, aspects and advantages of the present invention will become better understood with reference to the following description and appended claims.
A full and enabling disclosure of the present invention, including the best mode thereof, is set forth in the specification, which makes reference to the appended drawings, in which:
Reference now will be made in detail to embodiments of the invention, one or more examples of which are illustrated in the drawings. Each example is provided by way of explanation of the invention, not limitation of the invention. In fact, it will be apparent to those skilled in the art that various modifications and variations can be made in the present invention without departing from the scope or spirit of the invention. For instance, features illustrated or described as part of one embodiment, can be used with another embodiment to yield a still further embodiment. Thus, it is intended that the present invention encompass such modifications and variations as come within the scope of the appended claims and their equivalents.
For reference and an understanding of an environment in which the present conveyor assembly may be used, the system 10 of
Referring to
The vacuum chamber 12 also includes a plurality of interconnected cool-down modules 20 within the vacuum chamber 12 downstream of the vapor deposition apparatus 60. The cool-down modules 20 define a cool-down section within the vacuum chamber 12 in which the substrates 14 having the thin film of sublimed source material deposited thereon are allowed to cool at a controlled cool-down rate prior to the substrates 14 being removed from the system 10. Each of the modules 20 may include a forced cooling system wherein a cooling medium, such as chilled water, refrigerant, or other medium is pumped through cooling coils configured with the modules 20.
In the illustrated embodiment of system 10, at least one post-heat module 22 is located immediately downstream of the vapor deposition apparatus 60 and before the cool-down modules 20. The post-heat module 22 maintains a controlled heating profile of the substrate 14 until the entire substrate is moved out of the vapor deposition apparatus 60 to prevent damage to the substrate, such as warping or breaking caused by uncontrolled or drastic thermal stresses. If the leading section of the substrate 14 were allowed to cool at an excessive rate as it exited the apparatus 60, a potentially damaging temperature gradient would be generated longitudinally along the substrate 14. This condition could result in breaking, cracking, or warping of the substrate from thermal stress.
As diagrammatically illustrated in
Still referring to
An exit vacuum lock station is configured downstream of the last cool-down module 20, and operates essentially in reverse of the entry vacuum lock station described above. For example, the exit vacuum lock station may include an exit buffer module 42 and a downstream exit lock module 44. Sequentially operated slide valves 34 are disposed between the buffer module 42 and the last one of the cool-down modules 20, between the buffer module 42 and the exit lock module 44, and between the exit lock module 44 and an exit conveyor 46. A fine vacuum pump 38 is configured with the exit buffer module 42, and a rough vacuum pump 32 is configured with the exit lock module 44. The pumps 32, 38 and valves 34 are sequentially operated to move the substrates 14 out of the vacuum chamber 12 in a step-wise fashion without loss of vacuum condition within the vacuum chamber 12.
System 10 also includes a conveyor system configured to move the substrates 14 into, through, and out of the vacuum chamber 12. In the illustrated embodiment, this conveyor system includes a plurality of individually controlled conveyors 48, with each of the various modules including one of the conveyors 48. It should be appreciated that the type or configuration of the conveyors 48 in the various modules may vary. In the illustrated embodiment, the conveyors 48 are roller conveyors having driven rollers that are controlled so as to achieve a desired conveyance rate of the substrates 14 through the respective module and the system 10 overall.
As described, each of the various modules and respective conveyors in the system 10 are independently controlled to perform a particular function. For such control, each of the individual modules may have an associated independent controller 50 configured therewith to control the individual functions of the respective module. The plurality of controllers 50 may, in turn, be in communication with a central system controller 52, as illustrated in
Referring to
The vapor deposition apparatus 60 may take on various configurations and operating principles within the scope and spirit of the invention, and is generally configured for vapor deposition of a sublimated source material, such as CdTe, as a thin film on the PV module substrates 14. In the embodiment of the system 10 illustrated in
Referring to
In the illustrated embodiment, at least one thermocouple 74 is operationally disposed through the top wall of the deposition head 62 to monitor temperature within the head chamber adjacent or in the receptacle 66.
The receptacle 66 has a shape and configuration such that end walls 68 of the receptacle 66 are spaced from end walls 76 of the deposition head 62. The side walls of the receptacle 66 lie adjacent to and in close proximity to the side walls of the deposition head 62 (not visible in the view of
A heated distribution manifold 78 is disposed below the receptacle 66, and may have a clam-shell configuration that includes an upper shell member 80 and a lower shell member 82. The mated shell members 80, 82 define cavities in which heater elements 84 are disposed. The heater elements 84 heat the distribution manifold 78 to a degree sufficient for indirectly heating the source material within the receptacle 66 to cause sublimation of the source material. The heat generated by the distribution manifold 78 also aids in preventing the sublimated source material from plating out onto components of the deposition head 62. Additional heater elements 98 may also be disposed within the deposition head 62 for this purpose. Desirably, the coolest component within the deposition head 62 is the upper surface of the substrates 14 conveyed therethrough so that the sublimated source material is ensured to plate primarily on the substrates.
Still referring to
A distribution plate 88 is disposed below the manifold 78 at a defined distance above a horizontal plane of the upper surface of an underlying substrate 14, as depicted in
As previously mentioned, a significant portion of the sublimated source material will flow out of the receptacle 66 as transversely extending leading and trailing curtains of vapor. Although these curtains of vapor will diffuse to some extent in the longitudinal direction (direction of conveyance of the substrates) prior to passing through the distribution plate 88, it should be appreciated that it is unlikely that a uniform distribution of the sublimated source material in the longitudinal direction will be achieved. In other words, more of the sublimated source material will be distributed through the longitudinal end sections of the distribution plate 88 as compared to the middle portion of the distribution plate. However, as discussed above, because the system 10 conveys the substrates 14 through the vapor deposition apparatus 100 at a non-stop constant linear speed, the upper surfaces of the substrates 14 will be exposed to the same deposition environment regardless of any non-uniformity of the vapor distribution along the longitudinal aspect of the apparatus 60. The passages 86 in the distribution manifold 78 and the holes in the distribution plate 88 ensure a relatively uniform distribution of the sublimated source material in the transverse aspect of the vapor deposition apparatus 60. So long as the uniform transverse aspect of the vapor is maintained, a relatively uniform thin film layer is deposited onto the upper surface of the substrates 14.
As illustrated in
Still referring to
The embodiment of
Any suitable actuation mechanism 92 may be configured for moving the shutter plate 90 between the first and second operational positions. In the illustrated embodiment, the actuation mechanism 92 includes a rod 93 and any manner of suitable linkage that connects the rod 93 to the shutter plate 90. The rod 93 is externally rotated by any manner of mechanism located externally of the deposition head 62. The shutter plate 90 is particularly beneficial in that, for whatever reason, the sublimated source material can be quickly and easily contained within the deposition head 62 and prevented from passing through to the deposition area above the substrates 14 or conveyor assembly 100. This may be desired, for example, during start up of the system 10 while the concentration of vapors within the deposition head chamber builds to a sufficient degree to start the deposition process. Likewise, during shutdown of the system, it may be desired to maintain the sublimated source material within the deposition head 62 chamber to prevent the material from plating out on the conveyor or other components of the apparatus 60.
Referring to
Referring to
Conveyor 102 includes a plurality of interconnected slats 130. Each of the slats 130 has a respective flat planar outer surface 132 (
Referring again to the housing construction 104 depicted in
Referring particularly to
The housing 104, and conveyor 102 contained therein are configured for drop-in placement of the assembly 110 in the vapor deposition module 60. A plurality of braces 166 are attached to the side walls 106 and extend through slots in the top wall 110. These braces 166 define a plurality of lifting points for raising and lowering the assembly 100 into the casing 95 of the vapor deposition module 60. When maintenance is required, the entire conveyor assembly 100 is easily lifted from the module 60, and a spare assembly 100 is readily dropped in to replace the removed assembly 100. In this way, maintenance may be conducted on the removed assembly 100 while the processing line is returned to service. This keeps the vapor deposition line running in parallel with maintenance tasks. The conveyor assembly 100 sits on registration points within the casing 95 so that the different conveyor assemblies 100 are easily installed and removed.
Referring to
The top wall member 110 may also cooperate with the vapor deposition head 62 to add additional sealing. For example, the seals 96 discussed above at the longitudinal ends of the vapor deposition head 62 may engage against sealing surfaces 126 defined by the top wall 110. This sealing arrangement ensures that the sublimated source material that passes through the distribution plate 88 is maintained in the open deposition area 112 of the top member 110 and does not escape at the interface of the conveyor assembly 100 and vapor deposition head 62.
Referring again to
Tracks 144 are disposed along the upper leg of the conveyor 102 and provide a running surface for the conveyor rollers, as discussed in greater detail below. The tracks 144 may include tabs 145 that also extend through the side wall 106 and are engaged by pins 147.
The conveyor 102 may run in its endless loop path around sprockets 138 that are rotatably supported by the housing side walls 106. The sprockets 138 include teeth or cogs that engage with the conveyor rollers 142. At least one of the sprockets 138 is a driven sprocket, while the opposite sprocket is an idler sprocket. Typically, the upstream sprocket 138 serves as the idler sprocket.
In a particular embodiment, the conveyor slats 130 are interconnected by link assemblies 140. These link assemblies 140 may take on various configurations. A particularly unique configuration in accordance with aspects of the invention is illustrated in
Referring to
This written description uses examples to disclose the invention, including the best mode, and also to enable any person skilled in the art to practice the invention, including making and using any devices or systems and performing any incorporated methods. The patentable scope of the invention is defined by the claims, and may include other examples that occur to those skilled in the art. Such other examples are intended to be within the scope of the claims if they include structural elements that do not differ from the literal language of the claims, or if they include equivalent structural elements with insubstantial differences from the literal languages of the claims.
