Solar modules with back-contact photovoltaic cells interconnected by metal foils.

Abstract

The photovoltaic module includes a metal foil defining a number of electrical contacts, each electrically isolated from the other electrical contacts, and a number of back-contact photovoltaic cells overlaid on the metal foil and electrically connected via the number of electrical contacts. Each photovoltaic cell includes a first side configured to absorb light and a second side including a first conductive protrusion and a second conductive protrusion. The first conductive protrusion of a first one of the photovoltaic cells is in direct electrical communication with a first one of the number of electrical contacts, and the second conductive protrusion of the first one of the photovoltaic cells is in direct electrical communication with a second one of the electrical contacts.

Description

[Technical Field]

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS This application claims the benefit of U.S. Patent Application No. 62 / 861,973, filed June 14, 2019, which is incorporated herein by reference in its entirety.

[0002] Government Statement of Interest This invention was made with government support under DE-EE0007538 awarded by the U.S. Department of Energy. The government has certain rights in this invention.

[0003] The present invention relates to photovoltaic modules incorporating back-contact photovoltaic cells, metal foil electrical contacts, and methods for connecting the electrical contacts to the cells, and in particular to the architecture (materials and layer sequence) and fabrication (manufacturing methods and procedures) of the photovoltaic modules. [Background technology]

[0004] Photovoltaic cells in photovoltaic modules typically use metal, for example in the form of fingers and bus bars, to collect and transport photogenerated charge carriers with minimal resistive losses. However, metal on the front, or sun-facing, side of a photovoltaic cell reduces the cell's efficiency by reflecting incident light. Back-contact photovoltaic cells have most or all of their metal on their back (ground-facing) side, but can include cells with negative and positive polarity semiconductor regions on the backside, as well as cells with one or the other polarity region on the frontside, where the metal contacting this region wraps around through the cell's vias and reaches the backside.

[0005] There are several architectures and methods by which back-contact photovoltaic cells can be interconnected to form series and parallel electrical connections between adjacent cells in a module. In one example, a metal tabbing ribbon may be soldered to a bus bar on the photovoltaic cell, which may extend the length of the photovoltaic cell, for example. In another example, the metal on the back of each photovoltaic cell is made thick enough to conduct current across the width of the solar cell with minimal resistive losses, and the soldering of the metal tabbing ribbon only needs to be done at the edge of the cell. In yet another example, a metal foil is attached to the photovoltaic cell with a conductive adhesive. However, these architectures have disadvantages that increase cost and reduce efficiency, reliability, and energy yield. Summary of the Invention [Means for solving the problem]

[0006] The present disclosure relates to the design and manufacture of photovoltaic modules with back-contact photovoltaic cells, including material arrangements and methods of fabricating the arrangements, resulting in inexpensive, highly efficient and reliable photovoltaic modules.

[0007] The photovoltaic modules described herein include a metal foil that transports current with minimal resistance. This metal foil avoids the need for soldering tabbing ribbons or thick metal coatings on the photovoltaic cells, both of which have been used in back-contact photovoltaic modules to perform the same current-transporting function. The metal foil interconnects adjacent photovoltaic cells to form series and parallel electrical connections. The foil may be separated into segments so that only selected photovoltaic cells are interconnected, while others are electrically isolated by openings between sections of the foil. The metal foil makes low-resistance contact to metal areas on the photovoltaic cells, facilitated by laser welding, thin adhesives (without metal particles or flakes), or some combination. Attachment by laser welding or thin adhesives contributes to highly efficient and reliable metal foil-equipped modules.

[0008] The photovoltaic module architecture described herein facilitates attachment by laser welding or thin adhesive, both of which require areas of the metal foil to be in close proximity to or in direct contact with metal areas on the photovoltaic cell. In particular, embossing can make the areas of the metal foil that contact the photovoltaic cell stand out relative to the rest of the foil. Embossing is particularly useful when there is a sealing layer between the metal foil and the photovoltaic cell, which may have a thickness of between 10 μm and 800 μm, because the sealant can have openings that allow the embossed areas of the foil to pass through the sealing layer and make mechanical contact with the photovoltaic cell. Embossing can thus avoid the need for additional conductive material, such as a conductive adhesive, in the perforations of the sealing layer.

[0009] The methods described herein for fabricating back-contact photovoltaic modules involve stacking or piling up module materials and laminating the resulting stack. Some implementations include embossing a metal foil, applying a thin adhesive during stacking before placing the photovoltaic cells in the module stack, and laser welding the foil to the cells after module lamination.

[0010] In a first general aspect, a photovoltaic module includes a metal foil defining a number of electrical contacts, each electrically isolated from the other electrical contacts, and a number of back-contact photovoltaic cells overlaid on the metal foil and electrically connected via the number of electrical contacts. Each photovoltaic cell includes a first side configured to absorb light and a second side including a first conductive protrusion and a second conductive protrusion. The first conductive protrusion of a first one of the photovoltaic cells is in direct electrical communication with a first one of the number of electrical contacts, and the second conductive protrusion of the first one of the photovoltaic cells is in direct electrical communication with a second one of the electrical contacts.

[0011] Implementations of the first general aspect include one or more of the following features.

[0012] The plurality of electrical contacts includes pairs of adjacent electrical contacts, each separated by an opening through the metal foil. In some cases, the first conductive protrusion of the first one of the photovoltaic cells is laser welded to the first one of the plurality of electrical contacts. In some cases, the first conductive protrusion of the first one of the photovoltaic cells is adhered to the first one of the plurality of electrical contacts with a non-conductive adhesive.

[0013] In some cases, the metal foil is a metal foil layer. Each of the multiple electrical contacts is embossed such that an embossed portion of each of the multiple electrical contacts extends from the plane of the metal foil toward the multiple photovoltaic cells. Each embossed portion typically extends from the plane of the metal foil by a distance between 10 μm and 800 μm. A first conductive protrusion of a first one of the photovoltaic cells is in direct electrical communication with the embossed portion of a first one of the multiple electrical contacts, and a second conductive protrusion of the first one of the photovoltaic cells is in direct electrical communication with the embossed portion of a second one of the electrical contacts.

[0014] In some cases, an encapsulating layer is disposed between the metal foil and the plurality of photovoltaic cells, and each of the plurality of electrical contacts is embossed such that an embossed portion of each of the plurality of electrical contacts extends from the plane of the metal foil and through an opening in the encapsulating layer toward the plurality of photovoltaic cells, and the thickness of the encapsulating layer and the distance that each embossed portion extends from the plane of the metal foil are substantially the same.

[0015] The photovoltaic module may include a first outer layer and a second outer layer, where the metal foil and the plurality of photovoltaic cells are disposed between the first outer layer and the second outer layer. The photovoltaic module may include a first encapsulation layer between the first outer layer and the plurality of photovoltaic cells and a second encapsulation layer between the metal foil and the second outer layer.

[0016] In a second general aspect, manufacturing a photovoltaic module includes separating a metal foil into a plurality of electrically isolated electrical contacts; superimposing a plurality of photovoltaic cells over the plurality of electrical contacts, each photovoltaic cell comprising a first conductive protrusion and a second conductive protrusion; and forming a direct electrical coupling between the first conductive protrusion of a first one of the photovoltaic cells and a first one of the electrical contacts and between the second conductive protrusion of the first one of the photovoltaic cells and a second one of the electrical contacts.

[0017] Implementations of the second general aspect may include one or more of the following features.

[0018] Separating the metal foil may include removing portions of the metal foil (e.g., forming openings, such as elongated openings, in the metal foil). Removing portions of the metal foil may include laser ablation or mechanical milling of portions of the metal foil. The metal foil may be embossed prior to separating the metal foil into the plurality of electrical contacts. Embossing the metal foil creates an embossed portion for each of the multiple electrical contacts extending from the plane of the metal foil.

[0019] A second general aspect may further include forming an opening in an intermediate layer (e.g., a sealing layer) before embossing the metal foil, overlapping the metal foil and the intermediate layer, and embossing the metal foil through the opening in the intermediate layer. In some cases, the first conductive protrusion of the first one of the photovoltaic cells is laser welded to the first one of the electrical contacts. Forming a direct electrical coupling between the first conductive protrusion of the first one of the photovoltaic cells and the first one of the electrical contacts may include adhering the first conductive protrusion of the first one of the photovoltaic cells and the first one of the electrical contacts with a non-conductive adhesive. [Effects of the Invention]

[0020] The photovoltaic modules described herein with multiple back-contact photovoltaic cells can be interconnected with inexpensive metal foils, such as aluminum. As the spacing between the electrical connection points between the photovoltaic cells and the metal foil decreases, the amount of metal required on the photovoltaic cells to provide maximum resistance to charge carrier transport decreases, and current is carried in the foil instead of the metal on the photovoltaic cells. Metals applied directly to photovoltaic cells are typically more expensive than metals used as metal foils, potentially reducing the cost of the disclosed photovoltaic modules. A further advantage is the provision of low-resistance electrical interconnections between multiple back-contact photovoltaic cells and the metal foil with laser welding or thin adhesives, where electrical conduction occurs.

[0021] The details of one or more embodiments of the subject matter of this disclosure are set forth in the accompanying drawings and description. Other features, aspects, and advantages of the subject matter will become apparent from the description, drawings, and claims. [Brief explanation of the drawings]

[0022] [Figure 1] 1 is a cross-sectional view of a portion of a photovoltaic module. [Figure 2] 1 is a cross-sectional view of a portion of a photovoltaic module. [Figure 3] 1 is a cross-sectional view of a portion of a photovoltaic module. [Figure 4] FIG. 1 is an exploded view of a portion of a photovoltaic module. [Figure 5] FIG. 2 is an exploded cutaway view of a portion of a photovoltaic module. [Figure 6] FIG. 2 is an exploded cutaway view of a portion of a photovoltaic module. [Figure 7] FIG. 2 is a top view of a metal foil having a first arrangement of apertures and embossed portions. [Figure 8] FIG. 8 is a top view of the metal foil of FIG. 7 aligned and connected with a photovoltaic cell. [Figure 9] FIG. 9 is a top view of the photovoltaic cell of FIG. 8. [Figure 10]FIG. 10 is a top view of a metal foil having a second arrangement of apertures and embossed portions. [Figure 11] FIG. 11 is a top view of the metal foil of FIG. 10 aligned and connected with a photovoltaic cell. [Figure 12] FIG. 12 is a top view of the photovoltaic cell of FIG. [Figure 13] 1 illustrates the operation of a manufacturing sequence for a photovoltaic module. [Figure 14] 1 illustrates the current density-voltage characteristics of a photovoltaic module. [Figure 15] 1 illustrates the relative performance of photovoltaic modules as a function of time of moist heat exposure. [Figure 16] 1 illustrates the relative performance of a photovoltaic module as a function of the number of thermal cycles. [Figure 17] 1 illustrates the relative performance of photovoltaic modules as a function of the number of humidity-freeze cycles. DETAILED DESCRIPTION OF THE INVENTION

[0023] The present disclosure relates to a photovoltaic module comprising, from its first (front or sun-facing side) to its second (back or ground-facing side), a first outer layer, a first encapsulant, a plurality of back-contact photovoltaic cells, an intermediate layer, a metal foil separated into a plurality of electrically isolated electrical contacts, a second encapsulant, and a second outer layer. Each of these layers or elements may be separate prior to lamination and may be combined collectively or at an intermediate stage to form a cohesive module or laminate.

[0024] The first outer layer is formed from an optically transparent material, such as glass or plastic, that, when used in conjunction with other layers in a module, withstands the hail and wind-loading test specified in the Solar Module Product Qualification Test (e.g., IEC 61215). One example of a suitable glass is heat-strengthened, low-Fe, soda-lime glass. The thickness of the first outer layer is typically in the range of 1 mm to 5 mm or 2 mm to 4 mm (e.g., 3 mm). The first outer layer may have an anti-reflective coating. In one example, the anti-reflective coating includes silica particles deposited by a sol-gel or vacuum deposition process.

[0025] The first (or front) encapsulant typically includes one or more layers, such as an ethylene vinyl acetate (EVA) layer, a polyolefin (POE) layer, or both. Other suitable materials for the first encapsulant include materials capable of forming an optically transparent layer with a refractive index of approximately 1.5 during the lamination cycle (heat and pressure application). The first encapsulant may be between 10 μm and 800 μm thick and exhibit sufficient adhesion to the first outer layer and the photovoltaic cell to prevent delamination after ultraviolet (UV), thermal, and moisture content tests specified in solar module product qualification tests (e.g., IEC 61215).

[0026] A back-contact photovoltaic cell has positive and negative semiconductor regions that terminate in metal regions (cell metallization or conductive protrusions) on the second face (back or rear-facing side) of the cell. The cell metallization may comprise a metal such as silver, aluminum, or copper, screen-printed, vacuum-deposited, or plated. The positive and negative metallization regions may be distributed in a pattern on the second face of the cell. Examples of suitable patterns include an array of dots, interdigitated lines, and radial spokes. A dielectric layer may be applied in a pattern (e.g., by screen printing) over the positive and negative metallization regions, allowing groups of these regions to be connected together by a second layer of screen-printed or vacuum-deposited metal, by metal foil, or a combination thereof.

[0027] The interlayer typically comprises one or more polymeric materials positioned between the second side (or back) of the photovoltaic cell and the metal foil. The interlayer may be continuous or discontinuous. A first example of a suitable interlayer comprises one or more layers of encapsulant or adhesive, such as ethylene vinyl acetate (EVA) or polyolefin (POE) (e.g., between 10 μm and 800 μm thick). A second example of a suitable interlayer comprises a three-layer encapsulant stack (e.g., 10 μm to 100 μm thick) of a solid polymer sheet that does not melt at the lamination temperature, such as polyethylene terephthalate (PET), polyvinylidene fluoride (PVDF), or polytetrafluoroethylene (PTFE), sandwiched between two encapsulant layers (e.g., each 10 μm to 100 μm thick). A third example of a suitable intermediate layer includes a layer (e.g., 1 μm to 50 μm thick) of polymeric material that is liquid at room temperature and hardens at the lamination temperature (e.g., 130°C to 160°C) that is applied to the cell or foil electrical contacts by screen printing, jet dispensing, blade coating, etc.

[0028] The intermediate layer may be patterned. In one example, a suitable pattern includes perforations or openings in areas where electrical communication or direct contact is to be made between the conductive protrusions from the photovoltaic cell (e.g., metal coating, fingers, bus bars) and the metal foil. Patterning the intermediate layer to form perforations or openings may be achieved using a laser, a die, or other subtractive process. In some cases, the intermediate layer includes openings through which the metal foil is electrically coupled with the conductive protrusions of the photovoltaic cell during the lamination process.

[0029] The metal foil is separated into multiple electrical contacts. Each electrical contact is configured to be in direct electrical communication or coupling with a conductive protrusion of a back-contact photovoltaic cell in a photovoltaic module. As used herein, "direct electrical communication" or "direct electrical coupling" means that charge flows directly between the conductive protrusion of the photovoltaic cell and the metal foil in the absence of any intervening conductive material (e.g., in the absence of a conductive adhesive containing metal particles). Suitable thicknesses of the metal foil are typically in the range of 20 μm to 100 μm (e.g., 40 μm to 70 μm). Examples of suitable metals for the metal foil include copper, aluminum, or any combination thereof (e.g., copper-coated aluminum, copper or aluminum coated with an antioxidant or adhesion-promoting layer).

[0030] In some cases, the metal foil is embossed or otherwise deformed into a three-dimensional shape so that the portions of the metal foil intended to contact the conductive protrusions of the photovoltaic cell extend beyond (are not in the same plane as) the portions of the metal foil intended to be isolated from the metal areas on the photovoltaic cell. In particular, the embossed portions may protrude through perforations in the interlayer, such that the embossed portions of the metal foil are in direct electrical communication (e.g., in direct contact) with the conductive protrusions of the photovoltaic cell. The flat (non-embossed) portions of the metal foil may be isolated from the photovoltaic cell by the interlayer. The embossed portions of the metal foil may have the same or similar spatial pattern as some or all of the conductive protrusions on the photovoltaic cell, or they may have a different pattern. In other cases, the metal foil, particularly when used in conjunction with an interlayer that is liquid at room temperature and hardens during the lamination cycle, is flat (e.g., planar) and in direct electrical communication with the photovoltaic cell throughout, with no dielectric isolation layer over the cell.

[0031] Three-dimensional shaping of metal foils can be achieved by several methods. The first method involves embossing a free-standing foil using a mandrel or a single- or double-sided embossing die before attaching (by lamination or otherwise) the foil to an intermediate layer or second encapsulant. The second method involves attaching (by lamination or otherwise) the free-standing foil to an intermediate layer before molding, patterning the intermediate layer, and embossing the metal foil through the perforated areas of the intermediate layer using a mandrel or a single- or double-sided embossing die. The third method involves patterning the intermediate layer, embossing a free-standing metal foil through the perforated areas of the intermediate layer using a mandrel or a single-sided embossing die, and attaching (by lamination or otherwise) the shaped metal foil to the patterned intermediate layer.

[0032] Embossed or flat (e.g., planar) metal foils may be separated into multiple electrical contacts at one of several stages in the module manufacturing process. The separation achieves sufficient spacing between the electrical contacts so that they are electrically isolated from one another. In one example, after the metal foil is attached to the interlayer, ribbons having widths of about 1 mm to about 5 mm are removed from the metal foil by laser ablation, mechanical milling, or another means, resulting in the electrically isolated electrical contacts of the coplanar foil forming electrical contacts with 1 mm to 5 mm openings between their edges.

[0033] The separation may be performed so that the metal foil is separated into multiple electrical contacts having any desired shape, although a suitable shape facilitates interconnection of photovoltaic cells within a module. In particular, after the metal foil is connected to the photovoltaic cells, the separation of the metal foil provides a first electrical contact that electrically connects the negative polarity regions of the cells and is electrically isolated from the positive polarity regions of the cells, and a second electrical contact that electrically connects the positive polarity regions of the cells and is electrically isolated from the negative polarity regions of the cells. Additionally, to form a series interconnection, the separation of the foil may provide for the positive polarity region of a photovoltaic cell to be electrically connected to the negative polarity region of the next cell in the string. The separation of the metal foil electrical contacts provides electrical isolation from other adjacent cells. The separation of the metal foil electrical contacts provides electrical isolation of adjacent strings, and the string ends are oriented to allow connections that bypass the diodes in the junction box.

[0034] The second (or back) encapsulant typically includes one or more layers, such as an EVA layer, a POE layer, or both. The thickness of the second encapsulant typically ranges between 10 μm and 800 μm. The second encapsulant adheres to the metal foil and the second outer layer. The adhesion is sufficient to prevent delamination after UV, thermal, and moisture testing as specified in solar module product qualification tests (e.g., IEC 61215). The second outer layer may be optically transparent or optically opaque (e.g., white, black, or transparent), depending, at least in part, on the foil-to-photovoltaic cell interconnection method used. The second outer layer may define one or more openings. A junction box may be positioned adjacent each of the one or more openings. Each junction box provides an electrical connection point between the metal foil electrical contacts, the bypass diode, and the external lead in accordance with the photovoltaic module interconnection code. The transition between the external cable and the electrical contacts can be achieved in several ways, such as by soldering a copper bushing wire at one end to a component inside the junction box and connecting the other end to the end electrical contact of the metal foil (e.g., by the same method used to connect the foil to the cell or by another method such as resistance welding).

[0035] The photovoltaic module may be assembled in a manner similar to that used to assemble other types of photovoltaic modules, particularly those with conductive backsheets or metal foil electrical contacts. The second outer layer, second encapsulant, metal foil, and intermediate may be stacked or applied as appropriate, with their edges aligned. According to the method described above in which the metal foil may be embossed and separated, the metal foil may already be attached to the second encapsulant and second outer layer, or may be attached to a patterned intermediate layer, or a combination thereof. The photovoltaic cells may be placed on the intermediate layer in the appropriate position for their interconnection, for example, by a pick-and-place robot or another suitable means.

[0036] FIG. 1 is a cross-sectional view of a photovoltaic module 100. The photovoltaic module 100 has a first outer layer 102, a first encapsulant 104, a back-contact photovoltaic cell 106, an intermediate layer 108, a metal foil 110, a second encapsulant 112, and a second outer layer 114. The intermediate layer 108 is patterned and defines perforations. The metal foil 110 is embossed through the perforations in the intermediate layer. The second outer layer 114 is optically transparent.

[0037] The photovoltaic cells 106 can be disposed on the intermediate layer 108, and the first encapsulant 104 and first outer layer 102 are stacked on top of the photovoltaic cells. The stack of materials is heated and pressurized to form a laminate. Alternatively, any other suitable process can be used to remove air bubbles from the photovoltaic module 100, melt and crosslink or cure the encapsulant or adhesive layer, and bring the embossed areas of the metal foil 110 into closer contact with the conductive protrusions 116 of the photovoltaic cells 106. Direct electrical communication between the metal foil 110 and the conductive protrusions 116 on the photovoltaic cells 106 is achieved (e.g., after lamination) using a laser that welds the two metals together through the second outer layer 114 of the photovoltaic module 100, forming a laser weld 118. The laser can have any wavelength that is not significantly absorbed by the second outer layer 114 and the second encapsulant 112. Examples of suitable lasers include millisecond Nd:YAG lasers capable of delivering 30 mJ to 150 mJ per pulse, fiber optic lasers operating at frequencies between 10 kHz and 4 MHz, or any other laser that allows the metal of the foil electrical contacts to alloy with the metal on the cell.

[0038] The photovoltaic module 100 may include an edge seal around at least one edge of the module, a frame attached around at least one edge of the module, a mounting rail attached adjacent to a second outer layer of the module, a junction box attached to the second outer layer, or any combination thereof.

[0039] FIG. 2 is a cross-sectional view of a photovoltaic module 200. The photovoltaic module 200 includes a first outer layer 202, a first encapsulant 204, a photovoltaic cell 206, an intermediate layer 208, a metal foil 210, a second encapsulant 212, and a second outer layer 214. The intermediate layer 208 is a patterned encapsulant layer that defines perforations. The metal foil 210 is embossed through the perforations in the intermediate layer 208. The intermediate layer 208 also includes a layer of adhesive between the embossed areas of the metal foil 210 and the conductive protrusions 216 on the photovoltaic cell 206 to which the embossed metal foil 210 connects. The adhesive may be a room-temperature liquid that cures at lamination temperatures (130°C to 160°C), and it may be applied to either the embossed areas of the metal foil 210 or the conductive protrusions 216 on the photovoltaic cell 206. The adhesive may be applied to the metal foil 210 or to the photovoltaic cell 206 by any suitable means, such as screen printing and jet dispensing. The adhesive may be any material that is capable of bonding to the metal foil 210 and the conductive protrusions 216 of the photovoltaic cell 206.

[0040] Suitable adhesives are typically electrical insulators and are typically thin enough in at least some areas so that direct electrical communication (e.g., low-resistance electrical conduction) can occur between the conductive protrusions 216 of the photovoltaic cells 206 and the metal foil 210. In some cases, there is direct contact between the conductive protrusions 216 and the metal foil 210. The adhesive may be, for example, an epoxy, acrylate, or silicone, or any other suitable material. The surface morphology of the metal foil 210 may be modified by chemical or physical abrasion, or by the application of particles (e.g., by sintering), according to a pattern or over the entire surface, to create porous surface areas that promote bonding of the adhesive layer.

[0041] After the adhesive is applied to the desired areas and the photovoltaic cells 206 are disposed on the intermediate layer 208, the first encapsulant 204 and first outer layer 202 may be stacked onto the photovoltaic cells 206. The stack of materials may then be heated and pressurized to form a laminate. Alternatively, any other suitable process may be used to remove air bubbles from the photovoltaic module 200, melt and crosslink or cure the encapsulant or adhesive layers, and bring the embossed areas of the metal foil 210 into closer contact with the conductive protrusions 216 of the photovoltaic cells 206.

[0042] The photovoltaic module 200 may include an edge seal around at least one edge of the module, a frame attached around at least one edge of the module, a mounting rail attached adjacent to a second outer layer of the module, a junction box attached to the second outer layer, or any combination thereof.

[0043] FIG. 3 shows a cross-sectional view of a photovoltaic module 300. The photovoltaic module 300 includes a first outer layer 302, a first encapsulant 304, a photovoltaic cell 306, an intermediate layer 308, a metal foil 310, a second encapsulant 312, and a second outer layer 314. The intermediate layer 308 includes a layer of adhesive. The metal foil 310 is flat (i.e., not embossed). The photovoltaic cell 306 includes a dielectric layer that covers areas of a given polarity that are not intended for direct or electrical connection to the metal foil 310. The adhesive may be a room-temperature liquid that cures at lamination temperatures (130°C to 160°C) and may be applied to the metal foil 310 or the second side of the photovoltaic cell 306, covering some or all of the surface to which it is applied. The adhesive may be applied by, for example, screen printing, blade application, jet dispensing, or any other suitable method. The adhesive can be any material that is capable of bonding to the metal foil 310 and the conductive protrusions 316 of the photovoltaic cells 306 .

[0044] Although suitable adhesives are typically insulators, the adhesive layer can be thin enough in at least some areas so that low-resistance electrical conduction (direct electrical communication) can occur between the conductive protrusions 316 of the photovoltaic cells 306 and the metal foil 310. The adhesive can be, for example, an epoxy, acrylate, or silicone, or any other suitable material. The surface morphology of the metal foil 310 can be modified by following a pattern, across the surface, by chemical or physical abrasion, or by the application of particles (e.g., by sintering) to create a porous surface area that promotes bonding of the adhesive layer.

[0045] After the adhesive is applied and the photovoltaic cells 306 are disposed on the intermediate layer 308, the first encapsulant 304 and first outer layer 302 may be stacked on top of the photovoltaic cells 306. The stack of materials may then be heated and pressurized to form a laminate. Alternatively, any other suitable process may be used to remove air bubbles from the photovoltaic module 300, melt and crosslink or cure the encapsulant or adhesive layers, and bring the metal foil 310 into closer contact with the conductive protrusions 316 of the photovoltaic cells 306.

[0046] If, after lamination, the second outer layer 314 of the photovoltaic module 300 is optically transparent, a robust electrical connection between the metal foil electrical contacts and the conductive protrusions of the photovoltaic cells may optionally be formed using a laser that welds the two metals together through the transparent second outer layer of the module. The laser may have any wavelength that is not significantly absorbed by the second outer layer 314 and the second encapsulant 312. Examples of suitable lasers include millisecond Nd:YAG lasers capable of delivering 30 mJ to 150 mJ per pulse, fiber optic lasers operating at frequencies between 10 kHz and 4 MHz, or any other laser that allows the metal of the electrical contacts to alloy with the metal on the cells.

[0047] Figure 4 is an exploded view of a portion of a photovoltaic module 400. The photovoltaic module 400 includes a first outer layer 402, a first encapsulant 404, a back-contact photovoltaic cell 406, an intermediate layer 408, a metal foil 410, a second encapsulant 412, and a second outer layer 414. The metal foil 410 is separated along openings 416 into electrically isolated electrical contacts 418. Figure 4 depicts a portion of the photovoltaic module 400 during stacking, prior to lamination. After lamination, the encapsulant is compressed to bond adjacent layers together.

[0048] 5 is an exploded cutaway view of a portion of a photovoltaic module 500 with a back-contact photovoltaic cell 506, an intermediate layer 508, and a metal foil 510. The metal foil 510 is separated along openings 516 to electrically isolated planar electrical contacts 518. Extending from the electrical contacts 518 are embossed portions 520. The intermediate layer 508 includes perforations or openings 522 configured to allow the embossed portions 520 to form direct electrical communication (e.g., direct contact) with conductive protrusions extending from the photovoltaic cell 506.

[0049] 6 is an exploded cutaway view of a portion of a photovoltaic module 600 with a back-contact photovoltaic cell 606, an intermediate layer 608, and a metal foil 610. The metal foil 610 is separated along openings 616 into electrically isolated planar electrical contacts 618. Extending from the electrical contacts 618 are embossed portions 620. The intermediate layer 608 includes perforations or openings 622 configured to allow the embossed portions 620 to form direct electrical communication with conductive protrusions extending from the photovoltaic cell 606 through a non-conductive adhesive 624.

[0050] Figure 7 is a top view of a metal foil 710 having a first arrangement of openings 716, electrical contacts 718, and embossed portions 720. Figure 8 is a top view of the metal foil 710 of Figure 7 aligned and connected with four photovoltaic cells 806. Figure 9 is a top view of the photovoltaic cells 806 of Figure 8. An enlarged portion illustrates the bus bars 900, fingers 902, and dielectric regions 904.

[0051] Figure 10 is a top view of a metal foil 1010 having a second arrangement of openings 1016 and embossed portions 1020. Figure 11 is a top view of the metal foil 1010 of Figure 10 aligned and connected with four photovoltaic cells 1106. Figure 12 is a top view of the photovoltaic cells 1106 of Figure 11 illustrating conductive protrusions 1200.

[0052] Figure 13 depicts the operations of a manufacturing sequence for a photovoltaic module. At 1302, perforations are formed in the intermediate (encapsulating) layer. At 1304, a metal foil is embossed through the encapsulating layer, and the metal foil and encapsulating layer are bonded (e.g., glued). At 1306, the metal foil is separated to form electrical contacts, each electrically isolated from the other electrical contacts. At 1308, a second encapsulant and a second outer layer are overlaid on the metal foil and intermediate layer. At 1310, a photovoltaic cell is disposed on the intermediate layer. A bushing ribbon is threaded through the openings in the foil, second encapsulant, and second outer layer. At 1312, a first encapsulating layer and a first outer layer are overlaid on the photovoltaic cell. At 1314, the assembly (or stack) formed at 1312 is laminated. At 1314, direct electrical communication is achieved between the conductive protrusions of the photovoltaic cell and the metal foil by laser welding. Additional operations include trimming the edges of the laminate, framing the trimmed laminate, and applying a sealant. A junction box is bonded to the photovoltaic module, and the photovoltaic module may be tested.

[0053] Figure 14 illustrates the current density-voltage characteristics of a photovoltaic module. Figure 15 illustrates the relative performance of a photovoltaic module as a function of time of moist heat exposure. Figure 16 illustrates the relative performance of a photovoltaic module as a function of the number of thermal cycles. Figure 17 illustrates the relative performance of a photovoltaic module as a function of the number of humidity-freeze cycles.

[0054] While the present disclosure includes details of many specific embodiments, these should not be construed as limitations on the scope of the subject matter or on the scope that may be claimed, but rather as descriptions of features that may be inherent in particular embodiments. Certain features described in this disclosure in the context of separate embodiments may also be implemented in combination in a single embodiment. Conversely, various features described in the context of a single embodiment may also be implemented separately in multiple embodiments or in any suitable subcombination. Moreover, while the features described above may be described as acting in a certain combination and may initially be claimed as such, one or more features from a claimed combination may, in some cases, be deleted from the combination, and the claimed combination may be a subcombination or a variation of the subcombination.

[0055] Specific embodiments of the subject matter have been described. Other embodiments, modifications, and permutations of the described embodiments are within the scope of the following claims, as will be apparent to those skilled in the art. Although acts are depicted in figures or in the claims in a particular order, this should not be understood as requiring such acts to be performed in the particular order or sequence shown, or that all illustrated acts be performed (although some acts may be considered optional), to achieve desirable results.

[0056] Therefore, the above-described example embodiments do not limit or restrict the disclosure, and other variations, substitutions, and alterations are also possible without departing from the spirit and scope of the disclosure. [Explanation of symbols]

[0057] 100 Photovoltaic Modules 102 First Outer Layer 104 First sealant 106 Back-contact photovoltaic cells 108 Middle Class 110 Metal foil 112 Second sealant 114 Second Outer Layer 116 Conductive protrusion 118 Laser Welding 200 Photovoltaic Modules 202 First Outer Layer 204 First sealant 206 Photovoltaic Cells 208 Middle Class 210 Metal foil 212 Second sealant 214 Second Outer Layer 216 Conductive protrusion 300 Photovoltaic Modules 302 First Outer Layer 304 First sealant 306 Photovoltaic Cell 308 Middle Class 310 Metal foil 312 Second sealant 314 Second Outer Layer 316 Conductive protrusion 400 Photovoltaic Modules 402 First Outer Layer 404 First sealant 406 Back-contact photovoltaic cells 408 Middle Class 410 Metal foil 412 Second sealant 414 Second Outer Layer 416 Aperture 418 Electrical Contacts 500 Photovoltaic Modules 506 Back-contact Photovoltaic Cell 508 Middle Class 510 Metal foil 516 Aperture 518 Planar Electrical Contacts 520 Embossed part 522 Perforation, opening 600 Photovoltaic Modules 606 Back-contact photovoltaic cell 608 Middle Class 610 Metal foil 616 Aperture 618 Planar Electrical Contacts 620 Embossed part 622 Perforation, opening 624 Non-conductive adhesive 710 Metal foil 716 Aperture 718 Electrical Contacts 720 Embossed part 806 Photovoltaic Cell 900 Busbar 902 Finger 904 Dielectric Region 1010 Metal foil 1016 Aperture 1020 Embossed part 1106 Photovoltaic Cell 1200 Conductive protrusion

Claims

1. 1. A method of manufacturing a photovoltaic module, comprising: forming apertures in the intermediate layer before embossing the metal foil; superposing the metal foil and the intermediate layer; embossing the metal foil through the openings in the intermediate layer; separating the metal foil into a plurality of electrical contacts, each electrical contact being electrically isolated from each of the other electrical contacts; superimposing a plurality of photovoltaic cells over the plurality of electrical contacts, each photovoltaic cell comprising a first conductive protrusion and a second conductive protrusion; forming a direct electrical coupling between the first conductive protrusion of a first photovoltaic cell of the photovoltaic cells and a first electrical contact of the electrical contacts, and between the second conductive protrusion of the first photovoltaic cell of the photovoltaic cells and a second electrical contact of the electrical contacts.

2. The method of claim 1 , wherein the step of separating the metal foil comprises removing a portion of the metal foil.

3. The method of claim 2 , wherein removing the portion of the metal foil comprises laser ablation or mechanical milling the portion of the metal foil.

4. The method of claim 1 , further comprising the step of embossing the metal foil prior to separating the metal foil into the plurality of electrical contacts.

5. The method of claim 1 , wherein embossing the metal foil produces an embossed portion of each of the plurality of electrical contacts extending from a plane of the metal foil.

6. The method of claim 1 , further comprising laser welding the first conductive protrusion of the first photovoltaic cell of the photovoltaic cells to the first electrical contact of the electrical contacts.

7. 2. The method of claim 1, wherein the step of forming the direct electrical coupling between the first conductive protrusion of the first photovoltaic cell of the photovoltaic cells and the first electrical contact of the electrical contacts comprises adhering the first conductive protrusion of the first photovoltaic cell of the photovoltaic cells and the first electrical contact of the electrical contacts with a non-conductive adhesive.

8. The method of claim 1 , wherein the metal foil comprises aluminum.

9. The method of claim 1, wherein the thickness of the metal foil is in the range of 20 μm to 100 μm.

10. The method of claim 1, wherein the thickness of the metal foil is in the range of 40 μm to 70 μm.

11. The method of claim 1 , wherein the metal foil connects a positive polarity region of the first photovoltaic cell of the plurality of photovoltaic cells to a negative polarity region of a second photovoltaic cell of the plurality of photovoltaic cells.

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