Patent Application
20120234388
This invention relates to using a photovoltaic device with electrical breakdown protection.
A central challenge in cost-effectively providing breakdown protection in a photovoltaic device relates in part to the assembly processes used for photovoltaic cell manufacturing and the high cost associated with traditional diode devices being appropriately packaged for use in the solar industry. The size of the traditional packaging of diodes or other protection devices make them cumbersome to incorporate into the module at the cell level, and furthermore, such packaging introduces a variety of complexities for integrating such protection devices into traditional solar cells.
Furthermore, thin-film solar cells such as those comprised of CIGS or other IB-IIIA-VIA material have often not needed diodes as these cells when made on metal foil and were able to withstand hot spots without comprising the entire module. However, even with these cells, some issues remain that may be addressed by having breakdown protection.
Thus, there is a need for improved methods and devices for incorporating electrical breakdown protection device into photovoltaic cells.
The disadvantages associated with the prior art are overcome by embodiments of the present invention.
In one embodiment, a thin film solar cell with electrical breakdown protection.
Optionally, the device comprises a non-elongated, non-silicon thin-film solar cell using an electrically conductive foil substrate wherein the foil substrate carries current when the cell is forward biased, the substrate having a ratio of width to length greater than about 0.5 along an axis of current flow, and when exposed to light at AM 1.5G, the solar cell has an Impp greater than about 4 amps; an avalanche breakdown protection assembly to prevent the avalanche breakdown at the one or more locations by directing current through the protection unit.
Optionally, the device comprises an in-solar cell diode
Optionally, the device comprises packaging with top and bottom heat sink connectors, wherein the heat sinks are different layers of the same cell.
Optionally, the device comprises packaging with top and bottom heat sink connectors, wherein the heat sinks are different layers of different cells.
Optionally, the device comprises a total vertical height is about 180 to 500 microns or less
Optionally, the device comprises stack height is about 300 to 400 microns or less
Optionally, the device comprises a first area that is provided with a first material and a second area that is provided with a second material, wherein the first and second materials are different from one another, and wherein the first and second materials are selected from (a) materials that are electrically conductive, (b) materials that do not bond well to each other, (c) an interface material therebetween
said composition at least partially filling a cavity on the tab
Optionally, the device comprises a device for implantation in a solar cell comprising a diode, a first heat sink attachment having a triggerable adhesive property that allows the implantable device to adhere when exposed to a stimulus.
Optionally, the device comprises a tab having a bulk sub-region beneath the surface is activated to be become a solderable joint forming area and another area that is not substantially coated and not solderable when activated.
In another aspect, a method of breakdown protection assembly comprising:
providing a single reel of material which is pre-cut in a pattern so that a first portion of the material can be overlapped to a second portion of material to sandwich a breakdown protection device therebetween.
In one aspect, a solar module is described comprising: a solar cell string including a plurality of solar cells including a first solar cell and a second solar cell, each solar cell having a light receiving side and a back side, wherein the back side comprises a conductive substrate and wherein the plurality of solar cells are electrically interconnected in series using conductive leads which connect the light receiving side of one solar cell to the back side of an adjacent solar cell; a bypass diode device attached to the solar cell string, the bypass diode device including a bypass diode having a first and second leads, and first and second conductive strips each electrically connected at one end to one of the first and second leads respectively and each electrically connected at another end to a first conductive substrate of the first solar cell and a second conductive substrate of the second solar cell, respectively; an encapsulant having a frontside and a backside that encapsulates the solar cell string and the bypass diode device; and a protective shell sealing the encapsulated string, the protective shell including a transparent front protective layer, a back protective layer and a moisture barrier seal extending between and sealing edges of the transparent front protective layer and the back protective layer, wherein the transparent front protective sheet is placed over the light receiving side of the plurality solar cells and the frontside of the encapsulant and the back protective sheet is placed under the first and second conductive substrates, the by pass diode device and the backside of the encapsulant such that the bypass diode is located between the back protective sheet and housed in openings of conductive substrates of the plurality of solar cells.
In another aspect, a method of manufacturing a solar module is described comprising: providing a front protective layer having a front surface and a back surface, wherein the front protective layer is transparent; placing a first encapsulant layer over the back surface of the front protective layer; placing a solar cell string over the first encapsulant layer, wherein the solar cell string includes a plurality of solar cells, each solar cell having a light receiving side and a back side, wherein the back side comprises a conductive substrate and wherein the plurality of solar cells are electrically interconnected in series using conductive leads which connect the light receiving side of one solar cell to the back side of an adjacent solar cell, and wherein the light receiving side of the solar cells face the first encapsulant layer; attaching a bypass diode device to the solar cell string, the bypass diode device including a first conductive strip and a second conductive strip each attached at one end to respective first and second leads of a bypass diode, wherein the bypass diode is electrically connected to a first conductive substrate of a first solar cell and a second conductive substrate of a second solar cell of the plurality of solar cells by the first conductive strip and the second conductive strip, respectively; placing a second encapsulant layer over the bypass diode device and the conductive substrates of the plurality of solar cells; placing a back protective sheet over the second encapsulant layer and sealing a peripheral gap between the periphery of the front protective sheet and the back protective sheet with a moisture barrier edge sealant, and thereby forming a pre-module structure; and subjecting the pre-module structure to heat and pressure to form the solar module.
In one embodiment, the present invention, due to its use of a flexible structure that utilizes solar cells that are made on a metallic foil substrate, allows use of the metallic foil substrate as the heat sink for the bypass diodes. Thus, bypass diodes placed over the back surface of the metallic substrates of the solar cells may be thermally coupled to the solar cell substrates and any heat generated by the bypass diode can easily be dissipated to the large area solar cell and eventually to outside of the module. This also allows usage of bypass diodes that are sized to correspond to the module current rating, or some small percentage greater than the module current rating for reliability reasons, such as 10% or 20% larger. It should be noted that the typical size of the solar cells made on flexible substrates as described herein are larger than about 100 cm.sup.2, whereas the typical size of the bypass diodes that correspond to the module current rating is less than 1 cm.sup.2. Therefore, the cell provides excellent heat sink properties to the bypass diode. This increases the long term reliability of the module.
A further understanding of the nature and advantages of the invention will become apparent by reference to the remaining portions of the specification and drawings.
It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the invention, as claimed. It may be noted that, as used in the specification and the appended claims, the singular forms “a”, “an” and “the” include plural referents unless the context clearly dictates otherwise. Thus, for example, reference to “a material” may include mixtures of materials, reference to “a compound” may include multiple compounds, and the like. References cited herein are hereby incorporated by reference in their entirety, except to the extent that they conflict with teachings explicitly set forth in this specification.
In this specification and in the claims which follow, reference will be made to a number of terms which shall be defined to have the following meanings:
“Optional” or “optionally” means that the subsequently described circumstance may or may not occur, so that the description includes instances where the circumstance occurs and instances where it does not. For example, if a device optionally contains a feature for a barrier film, this means that the barrier film feature may or may not be present, and, thus, the description includes both structures wherein a device possesses the barrier film feature and structures wherein the barrier film feature is not present.
Referring now to
Referring to
The packaging in one embodiment, creates an ultra-low profile assembly without the bulk of traditional die packaging and without encapsulant, as the entire module or panel will have an encapsulant layer when the module is laminated.
Referring now to
By way of nonlimiting example, the tabs 110 and 120 in this embodiment are configured wider than the diode since it is desirable for handling purposes and to have space for the welds or attachment areas 120. The present design is offset to allow for wide strips or tabs 110 and 120, but also not have the tabs 110 and 120 overlap each other when sandwiching the breakdown protection device 130 therebetween. In one embodiment, the tab 110 is a wide enough strip to weld or attach it to the cell, but other than the area occupied by the breakdown protection device 130, one does not want excess overlap with the tab 120, as there may be a risk of electrical shorting. This is due in part to the relatively small height separation such as 0.1 mm between the two tabs 110 and 120. There is a risk that during lamination, soldering, or assembly, the tabs 110 and 120 may press together if there are overhanging areas. In one embodiment, the tabs may be about 1-3 mm wide and about 2-10 mm long. Optionally, some embodiments may have tabs about 1-10 mm wide and about 2-50 mm long. Optionally, some embodiments may have tabs about 1-30 mm wide and about 2 mm to maximum length of the cell long. In one embodiment, the ratio of the thickness of the simultaneously thermal and electrical connectors 110 to the thickness of the bare die is about 1:10 to about 1:5. Optionally, the ratio of the thickness of the simultaneously thermal and electrical connectors 110 to the thickness of the bare die is about 1:12 to about 1:6. This allows for the strain or stress from thermal cycling and CTE to be absorbed by the tab 110 and/or 120. Thus the yield strength of the tab 110 in one embodiment, can be configured to be less than the yield strength of the solder joint between the die and the tab. Optionally, the yield strength of the tab in one embodiment, can be configured to be less than the yield strength of the bare die. Optionally, the yield strength of the tab in one embodiment, can be configured to be less than the fatigue limit of bare die after temperature cycling 500 cycles from −40 to 85 C. Optionally, the yield strength of the tab in one embodiment, can be configured to be less than the fatigue limit of solder joint between the tab and a surface of the die after temperature cycling 500 cycles from −40 to 85 C. This allows the tab to be a strain relief for the solder joint. In one embodiment, this strain relief is achieved by the thinness of the material of the tab. Thus, stress yields occur in the tab, not the die or the solder joint. In one embodiment, the thickness of the tabs may be in the range of about 0.100 mm to about 0.070 mm thick. Optionally, the thickness of the tabs may be in the range of about 0.120 mm to 0.050 mm thick. Optionally, the thickness of the tabs may be in the range of about 0.050 mm to 0.075 mm thick. Optionally, the thickness of the tabs may be in the range of about 0.040 mm to 0.060 mm thick. Optionally, the thickness of the tabs may be in the range of about 0.010 mm to 0.060 mm thick. Total stack height with all layers and the die can be about 0.200 mm to about 0.500 mm in vertical height.
In one embodiment, the tabs 110 and 120 is typically selected to be material this compatible with the material used for the cell. In one example, the material for the tabs may have a coefficient of thermal expansion that is the same or similar to the cell material. By way of nonlimiting example, the tab may be made of steel, carbon steel, stainless steel, aluminum, copper, molybdenum, their alloys, metallized polymers or plastics, single or multiple combinations of the foregoing, or the like. In one embodiment, if the heat sink layers in the cell are made of aluminum, the tabs 110 and 120 can also be made of aluminum such as but not limited to 1000 series aluminum.
It should be understood that in many embodiments, the tabs 110 and 120 are at least partially cladded, plated, mechanically pressed, or otherwise provided with an electrically conductive material on one side. In one embodiment, this treated area is typically shaped to match the area where the breakdown protection device 130 will be placed or sandwiched between the tabs 110 and 120. Optionally, a greater area or only select areas are cladded or treated within the area where the breakdown protection device 130 will be placed. In one embodiment, the tabs 110 and 120 are cladded directly with solder. Optionally, they may be cladded with a material that is not solder, but can be soldered to or has good electrical conductivity. In one embodiment, the system may comprise of a copper layer that is an interface layer between an aluminum tab and a solder layer. Some embodiments may optionally recess a portion of the tab 110 so that the interface layer and the solder layer remain within the shape of the original tab (which may be a rectangular profile).
For example, if the tabs 110 and 120 comprise of aluminum, a cladded/plated different metal is plated or otherwise attached to the aluminum foil. Then aluminum is welded to cell. For an aluminum foil tab, the aluminum is cleaned first and then the cladding or plated material is applied before a native oxide of aluminum can form. The cladding using a different material from that of the tab, creates an interface surface to facilitate the transition from the material of the tab to that of the die, which would otherwise be incompatible. In one embodiment, this interface surface is a non-solder, electrically conductive material.
Preferably, but not necessarily, the tabs 110 and 120 can come presoldered or with solder material thereon. One non-limiting example will put down nickel, then copper, then tin-silver solder or some combination thereof. Of course, it should be understood that any of a variety of types of solders may be used and the present embodiment is not limited to any particular one. For example, some embodiments may use tin, copper, silver, bismuth, indium, zinc, antimony, or other metal based solders. The solder may include flux or it may be flux free. The assembly of the tabs 110, 120 and the breakdown protection device 130 occurs when the assembly is pressed together, heated and thus soldered to form a breakdown protection assembly.
Optionally, for attachment of the tabs to the solar cell, some embodiments may use soldering in addition with or in combination with welding to attach the tabs 110 and 120 to the cell. It should be understood that the cell is such a heat sink that to quickly solder to cell requires a minimum tack time that will typically take several seconds. Using methods such as spot welding, 0.1 to 0.3 seconds tact time can be achieved. The large heat sink effect of the cells, while desirable once the die is attached, presents a challenge to achieving that attachment during assembly.
Referring to
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a through 10v show a variety of other configurations wherein the breakdown protection device 130 is sandwiched between tabs of various shapes, orientations, cutouts, or the like. For example,
Referring now to
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As see in
This overlap (by one or both tabs) results in a “zipper” action wherein the center areas are brought together. Into the overlap one can squeeze in the diode or device 130. Or, as previously mentioned, some may put the diode on first, then overlap and press together.
Referring now to
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It should be understood that a variety of post assembly processing such as but not limiting testing, further heating to improve solder contact, or the like may be used after the breakdown protection device is placed into the assembly.
Referring to
Referring to
Optionally, the total thickness of the tabs 110 and 120 is minimized to allow for CTE mismatch between tabs, solder and die without over-stressing the die or solder and preventing the creation of cracks in the die or solder during manufacture and operation of the butterfly diode assembly. The tab thicknesses and material properties can be selected to exert low force on the solder joint and die with or without the tabs reaching stresses above the tab material yield stress. In one case, the tabs 110 and 120 have material thickness (with or without solder) in the range of 0.001 mm to 0.100 mm, depending on tab, solder and die materials.
Optionally, the solar cell acts as a heat sink during the diode operation. In this assembly, this embodiment has created a power diode which high current capability (10 amps or more) that has heat sinks on both sides (top and bottom) which is also unusual. Optionally, some embodiments may have at least 5 amp rating on the diode.
Referring to
The device layers 302, 312 are preferably of a type that can be manufactured on a large scale, e.g., in a roll-to-roll processing system. There are a large number of different types of device architectures that may be used in the device layers 302, 312. By way of example, and without loss of generality, the inset in
Some embodiments can use diodes selected from one or more the following:
Typical lamination temperatures of 150-170 C and lamination times of 1-15 minutes are adequate to laminate the module as well as cure the conductive adhesives to achieve the proper electrical integration of the bypass diode devices into the module. It should be noted that this approach of applying the conductive adhesive first and curing it during.
Linearly placed bypass diode devices may be placed at any location over the back or bottom surface of the solar cells, including right over the conductive ribbons. Some embodiments may use thermally conductive adhesives include but are not limited to products sold by Resinlab (such as product No. EP 1121, which forms a flexible layer as desired in this application) and Dow Corning (such as product Nos. SE4450, 1-4173, and 3-6752). Thermally conductive transfer tapes provided by 3M company are also appropriate for this application
Some embodiments may have by-pass diodes for every three cells, every two cells or even every cell for safe and efficient operation. As used herein, the term “substantially congruent” means that the shape and size of a complementary cutout is about the same, within manufacturing tolerances for fabricating the complementary cutout, as the shape and size of a gap region when the complementary cutout is superimposed on the gap region. In cell architecture through an opening, wherein base of diode is not directly connected to the cell, but to a tab and then to a cell so that the surface tab directly beneath the die and facing the cell layer is free floating and thus can minimizing stress concentration.
The typical thickness of the active diode region 501 may be in the range of 0.05-0.3 mm, which thickness includes both the p-type semiconductor layer and the n-type semiconductor layer. The width of the leads may be in the range of 1-10 mm depending on the current rating of the module within which the bypass diode devices D would be employed. The typical width of the leads may be in the range of 2-6 mm. Since the bypass diode devices D are placed on the bottom or back, un-illuminated side of the solar cells or the circuit, wide leads do not contribute to any power loss from the module.
Thus, bypass diodes placed over the back surface of the metallic substrates of the solar cells may be thermally coupled to the solar cell substrates and any heat generated by the bypass diode can easily be dissipated to the large area solar cell and eventually to outside of the module. This also allows usage of bypass diodes that are sized to correspond to the module current rating, or some small percentage greater than the module current rating for reliability reasons, such as 10% or 20% larger. It should be noted that the typical size of the solar cells made on flexible substrates as described herein are larger than about 100 cm2, whereas the typical size of the bypass diodes that correspond to the module current rating is less than 0.5 cm2. Therefore, the cell provides excellent heat sink properties to the bypass diode. This increases the long term reliability of the module.
While the invention has been described and illustrated with reference to certain particular embodiments thereof, those skilled in the art will appreciate that various adaptations, changes, modifications, substitutions, deletions, or additions of procedures and protocols may be made without departing from the spirit and scope of the invention. For example, with any of the above embodiments, it should be understood that they are not limited to incorporation only on the backside of the solar. Some may incorporate the diode or breakdown protection device on the side or the front of the solar cell. In one embodiment, a group IB-IIIA-VIA or other material maybe used as the voltage breakdown protection device. This device maybe used with a photovoltaic material made of the same material (in the same or different molar percentages). Optionally, thin-film material may be used as breakdown protection for silicon or other types of photovoltaic devices. Some embodiments may use just a single tab embodiment, not a dual tab. Some may use a corner placement of diode. Optionally, stress is absorbed by the tab, not the welds (based on but not limited to thickness reduction and CTE matching material to the heat sink layer(s)). Optionally, creating a multi layer assembly with a bare die having a yield member that is also an electrical connector and thermal connector. Optionally, using a void prevention element in the tab architecture. As used herein, the term “substantially rectangular shape” means that the shape is that of a rectangle within manufacturing tolerances for fabricating a rectangular shape. Some embodiment can use tabs with one or more the following layers: copper strip, Cu, plated with tin, Sn, or nickel, Ni. Optionally, non-height, non lateral space taking configuration is sued for the die placement.
Furthermore, those of skill in the art will recognize that any of the embodiments of the present invention can be applied to almost any type of solar cell material and/or architecture. For example, the absorber layer in solar cell 10 may be an absorber layer comprised of silicon, amorphous silicon, copper-indium-gallium-selenium (for CIGS solar cells), CdSe, CdTe, ZnTe, CdZnTe, Cu(In,Ga)(S,Se)2, Cu(In,Ga,Al)(S,Se,Te)2, other absorber materials, IB-IIB-IVA-VIA absorbers, or other alloys and/or combinations of the above, where the active materials are present in any of several forms including but not limited to bulk materials, micro-particles, nano-particles, or quantum dots. The CIGS cells may be formed by vacuum or non-vacuum processes. The processes may be one stage, two stage, or multi-stage CIGS processing techniques. Additionally, other possible absorber layers may be based on amorphous silicon (doped or undoped), a nanostructured layer having an inorganic porous semiconductor template with pores filled by an organic semiconductor material (see e.g., US Patent Application Publication US 2005-0121068 A1, which is incorporated herein by reference), a polymer/blend cell architecture, organic dyes, and/or C60 molecules, and/or other small molecules, micro-crystalline silicon cell architecture, randomly placed nanorods and/or tetrapods of inorganic materials dispersed in an organic matrix, quantum dot-based cells, or combinations of the above. Many of these types of cells can be fabricated on flexible substrates.
Additionally, concentrations, amounts, and other numerical data may be presented herein in a range format. It is to be understood that such range format is used merely for convenience and brevity and should be interpreted flexibly to include not only the numerical values explicitly recited as the limits of the range, but also to include all the individual numerical values or sub-ranges encompassed within that range as if each numerical value and sub-range is explicitly recited. For example, a size range of about 1 nm to about 200 nm should be interpreted to include not only the explicitly recited limits of about 1 nm and about 200 nm, but also to include individual sizes such as 2 nm, 3 nm, 4 nm, and sub-ranges such as 10 nm to 50 nm, 20 nm to 100 nm, etc. . . . .
The publications discussed or cited herein are provided solely for their disclosure prior to the filing date of the present application. Nothing herein is to be construed as an admission that the present invention is not entitled to antedate such publication by virtue of prior invention. Further, the dates of publication provided may be different from the actual publication dates which may need to be independently confirmed. All publications mentioned herein are incorporated herein by reference to disclose and describe the structures and/or methods in connection with which the publications are cited. For example, U.S. patent application Ser. Nos. 11/207,157 filed Aug. 16, 2005 and 12/064,031 filed Aug. 16, 2006 are fully incorporated herein by reference for all purposes.
While the above is a complete description of the preferred embodiment of the present invention, it is possible to use various alternatives, modifications and equivalents. Therefore, the scope of the present invention should be determined not with reference to the above description but should, instead, be determined with reference to the appended claims, along with their full scope of equivalents. Any feature, whether preferred or not, may be combined with any other feature, whether preferred or not. In the claims that follow, the indefinite article “A”, or “An” refers to a quantity of one or more of the item following the article, except where expressly stated otherwise. The appended claims are not to be interpreted as including means-plus-function limitations, unless such a limitation is explicitly recited in a given claim using the phrase “means for.”
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/US2010/046877 | 8/26/2010 | WO | 00 | 6/6/2012 |
| Number | Date | Country | |
|---|---|---|---|
| 61237295 | Aug 2009 | US | |
| 61247526 | Sep 2009 | US |
