Patent Publication Number: US-2019181294-A1

Title: Wire network for interconnecting photovoltaic cells

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of and claims priority to U.S. patent application Ser. No. 14/822,712, titled “WIRE NETWORK FOR INTERCONNECTING PHOTOVOLTAIC CELLS” filed on Aug. 10, 2015, which is a divisional of U.S. patent application Ser. No. 13/087,724 (now abandoned), titled “WIRE NETWORK FOR INTERCONNECTING PHOTOVOLTAIC CELLS,” filed Apr. 15, 2011, which is a continuation-in-part of U.S. patent application Ser. No. 12/566,555 (now abandoned), titled “INTERCONNECT ASSEMBLY,” filed Sep. 24, 2009, which is a continuation-in-part of U.S. patent application Ser. No. 12/052,476 (issued as U.S. Pat. No. 8,912,429), titled “INTERCONNECT ASSEMBLY,” filed Mar. 20, 2008, each of which is incorporated herein by reference in its entirety and for all purposes. 
    
    
     BACKGROUND 
     In the drive for renewable sources of energy, photovoltaic technology has assumed a preeminent position as a cheap and renewable source of clean energy. For example, photovoltaic cells using a Copper Indium Gallium Diselenide (CIGS) absorber layer offer great promise for thin-film photovoltaic cells having high efficiency and low cost. Of comparable importance to the technology used to fabricate thin-film cells themselves is the technology used to collect electrical current from the cells and to interconnect one photovoltaic cell to another to form a photovoltaic module. 
     Just as the efficiency of thin-film photovoltaic cells is affected by parasitic series resistances, photovoltaic modules fabricated from multiple cells are also impacted by parasitic series resistances and other factors caused by electrical connections to the absorber layer and other electrical connections within the modules. A significant challenge is the development of current collection and interconnection structures that improve overall performance of the module. Moreover, the reliability of photovoltaic modules is equally important as it determines their useful life, cost effectiveness, and viability as reliable alternative sources of energy. 
     SUMMARY 
     Provided are novel interconnect wire network assemblies and methods of fabricating thereof. An assembly may include conductive portions/individual wires that, in certain embodiments, are substantially parallel to each other. The assembly also includes two or more carrier films (i.e., the front side and back side films) attached to opposite sides of the wires. The films are typically attached along the wire ends. The films are made from electrically insulating materials and at least the front side film is substantially transparent. The front side film is used to attach the wires to a photovoltaic surface of one cell, while the back side film is used for attachment to a substrate surface of another cell. These attachments electrically interconnect the two cells in series. In certain embodiments, one or both carrier films extend beyond two end wires and form insulated portions that allow much closer arrangements of the cells in a module. 
     In certain embodiments, an interconnect wire network assembly includes a plurality of conductive portions extending substantially parallel to each other, a first carrier film having a first substantially transparent electrically insulating layer, and a second carrier film having a second substantially transparent electrically insulating layer. The plurality of conductive portions having a first set of ends defining a first edge and a second set of ends defining a second edge. The plurality of conductive portions is configured for current collection from a front side surface of a first photovoltaic cell and electrical connection with a back side surface of a second photovoltaic cell. The first carrier film is coupled to the plurality of conductive portions along the first edge and configured to attach the plurality of conductive portions to the front side surface of the first photovoltaic cell to form a first electrical connection between the front side surface and the plurality of conductive portions. The second carrier film is coupled to the plurality of conductive portions along the second edge and configured to attach the plurality of conductive portions to the back side surface of the second photovoltaic cell to form a second electrical connection between the back side surface and the plurality of conductive portions. 
     In certain embodiments, a first carrier film is positioned on another side of the conductive portions with respect to the second carrier film. The two films may overlap. In other embodiments, the two films may be positioned at a predetermined distance from the second carrier film. An outside edge of the first carrier film may substantially coincide with the first edge of the plurality of conductive portions. In other embodiments, the first carrier film extends past the first edge of the conductive portions. In certain embodiments, conductive portions extend past two edges of the first carrier film. 
     One or both carrier films may be made from one or more of the following materials: polyethylene terephthalate, polyethylene co-methacrylic acid, polyamide, and polyetheretherketone. In the same or other embodiments, conductive portions may be made from one or more of the following materials: copper, aluminum, nickel, and chrome. Conductive portions may include multiple individual wires. These individual wires may be between 24 gauge and 56 gauge. The individual wires may be spaced apart by between about 2 millimeters and about 5 millimeters. Each wire may be electrically insulated from other wires prior to attaching the interconnect wire network assembly to the first photovoltaic cell or the second photovoltaic cell. In certain embodiments, multiple individual wires have a strip of foil attached to the second edge and electrically interconnecting the multiple individual wires. 
     In certain embodiments, the first carrier film extends past two end wires of the plurality of conductive portions forming two side insulating regions. The first carrier film may extend past and folds over two end conductive portions of the plurality of conductive portions, forming insulating shells around the two end conductive portions. 
     Provided also a method of fabricating an interconnect wire network assembly. The method involves unwinding multiple individual wires from corresponding multiple wire rolls, extending the wires along an unwinding direction substantially parallel to each other at a predetermined distance from each other, applying a first carrier film onto the first surface of the wires, and applying a second carrier film onto the second surface of the wires. The two first carrier films may be applied substantially perpendicular to the unwinding direction. Applying the first carrier film may involve passing an electric current through a portion of the multiple individual wires that is in contact with the first carrier film in order to heat this portion. 
     The method may also involve forming a roll of interconnect wire network subassemblies, unwinding the roll of interconnect wire network subassemblies, and cutting the multiple individual wires substantially perpendicular to the multiple individual wires to form the interconnect wire network assembly. In certain embodiments, the method involves cutting the multiple individual wires substantially perpendicular to the multiple individual wires to form the interconnect wire network assembly. Such cutting may also involve cutting the first carrier film or the second carrier film. 
     Provided also a photovoltaic module that includes a first photovoltaic cell having a front side surface, a second photovoltaic cell having a back side surface, and an interconnect wire network assembly. The assembly may include a plurality of conductive portions extending substantially parallel to each other and in electrical communication with the front side of the first photovoltaic cell and the back side of the second photovoltaic cell. The assembly also includes a first carrier film coupled to the plurality of conductive portions along the first edge and attaching the plurality of conductive portions to the front side surface of the first photovoltaic cell. Furthermore, the assembly includes a second carrier film coupled to the plurality of conductive portions along the second edge and attaching the plurality of conductive portions to the back side surface of the second photovoltaic cell. The conductive portions include a first set of ends defining the first edge and a second set of ends defining the second edge. The first carrier film is made from a first substantially transparent electrically insulating layer, while the second carrier film is made from a second substantially transparent electrically insulating layer. 
     These and other embodiments are described further below with reference to the figures. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic representation of a photovoltaic module having multiple photovoltaic cells electrically interconnected with each other using interconnect wire network assemblies, in accordance with certain embodiments. 
         FIG. 2  is a schematic top view of an interconnect wire network assembly, in accordance with certain embodiments. 
         FIG. 3A  is a schematic side view of an interconnect wire network assembly depicted in  FIG. 2 , in accordance with certain embodiments. 
         FIG. 3B  is a schematic side view of another interconnect wire network assembly, in accordance with different embodiments. 
         FIG. 3C  is a schematic side view of yet another interconnect wire network assembly, in accordance with different embodiments. 
         FIG. 4  illustrates a process flowchart corresponding to a method of fabricating an interconnect wire network assembly, in accordance with certain embodiments. 
         FIG. 5  illustrates a schematic view of an apparatus for fabricating an interconnect wire network assembly, in accordance with certain embodiments. 
         FIG. 6A  is a schematic representation of a technique for cutting a subassembly to form an interconnect wire network assembly, in accordance with certain embodiments. 
         FIG. 6B  is a schematic representation of another technique for cutting a subassembly to form an interconnect wire network assembly, in accordance with different embodiments. 
         FIG. 7  illustrates a schematic side view of two photovoltaic cells electrically interconnected using an interconnect wire network assembly, in accordance with certain embodiments. 
     
    
    
     DETAILED DESCRIPTION OF EXAMPLE EMBODIMENTS 
     In the following description, numerous specific details are set forth in order to provide a thorough understanding of the present invention. The present invention may be practiced without some or all of these specific details. In other instances, well known process operations have not been described in detail so as to not unnecessarily obscure the present invention. While the invention will be described in conjunction with the specific embodiments, it will be understood that it is not intended to limit the invention to the embodiments. 
     To provide a better understanding and context for the description of various features of interconnect wire network assemblies, an example of a photovoltaic module will now be described.  FIG. 1  is a schematic representation of a photovoltaic module  100  having multiple photovoltaic cells  104 , in accordance with certain embodiments. Photovoltaic cells  104  are electrically interconnected in series using multiple interconnect wire network assemblies  106 . Specifically, each pair of cells  104  is interconnected using one assembly  106 .  FIG. 1  shows eight photovoltaic cells interconnected with seven assemblies; however, it will be understood that any number of cells may be used in a module. In certain embodiments, a module includes at least 10 cells or, more specifically, at least 15 cells interconnected in series. In particular embodiments, a module includes 22 cells interconnected in series. Furthermore, one set of cells interconnected using wire network assemblies may be further connected to one or more similar sets in the same module. For example, a module may include two sets, each set including 22 interconnected cells. The connections between the sets may be provided by wire network assemblies or other components. 
     Multiple cells may be interconnected in series when individual cells do not provide an adequate output voltage. The output voltage requirement may be driven by electrical current transmission and other factors. For example, a typical voltage output of an individual CIGS cell is between 0.4V and 0.7V. A module built from CIGS cells is often designed to provide a voltage output of at least about 20V or even higher. In addition to interconnecting multiple cells in series, a module may include one or more module-integrated inverters. Interconnect wire network assemblies  106  may be also used to provide uniform current distribution and collection from one or both contact layers, as further explained below. It should be understood that these assemblies may also be used to provide parallel electrical connections or a combination of in-series and parallel connections. 
     As shown in  FIG. 1 , each interconnect wire network assembly  106  (with the exception of the bottom assembly, which is further described above) extends over a front side of one cell and under a back side of another cell. One or both cells in this pair may be connected to other cells and so on. As such, most cells may have one interconnect wire network assembly extending over its front side and another interconnect wire network assembly extending under its back side. An end cell in the set (e.g., the top-most cell in  FIG. 1 ) may have only one interconnect wire network assembly extending over one of its surfaces, typically over the front side. In this embodiment, a bus bar  108  may be connected directly to the cell (i.e., to its back side). In some embodiments, an end cell (e.g., the bottom-most cell in  FIG. 1 ) may still have two interconnect wire network assemblies. A bus bar  110  may be attached to one of these assemblies. Specifically, bus bar  110  may be attached to a portion of the interconnect wire network assembly extending outside of the cell perimeter. Such attachment may involve welding, soldering, and other forms of attachments, which are generally not suitable for attachment directly to the cells. 
     When an interconnect wire network assembly extends over a front side of the photovoltaic cell, it makes an electrical connection with that side or, more specifically, with a top layer arranged on that side. In certain embodiments, a photovoltaic cell includes one or more transparent conductive oxides (TCO), such as zinc oxide, aluminum-doped zinc oxide (AZO), indium tin oxide (ITO), and gallium doped zinc oxide, disposed over the front side of the photovoltaic cell. A typical thickness of a top conductive layer is between about 100 nanometers to 1,000 nanometers (for example between about 200 nanometers and 800 nanometers), with other thicknesses within the scope. The TCO provides an electrical connection between the entire photovoltaic layer and a portion of the interconnect wire network assembly extending over the front side of the cell. Due to the limited conductivity of the TCO layer, the interconnect wire network assembly typically extends uniformly over the entire front side surface of the cell and provides uniform current distribution and collection from this surface. As such, an interconnect wire network assembly is sometimes referred to as a current collector. Various characteristics of interconnect wire network assemblies allowing uniform current distribution and collection are described below in the context of  FIG. 2 . 
     An interconnect wire network assembly extending under a back side of the cell makes an electrical connection with that side or more specifically with a conductive substrate supporting the photovoltaic stack. Some examples of photovoltaic stacks include CIGS cells, cadmium-telluride (Cd—Te) cells, amorphous silicon (a-Si) cells, micro-crystalline silicon cells, crystalline silicon (c-Si) cells, gallium arsenide multi-junction cells, light adsorbing dye cells, and organic polymer cells. Some examples of conductive substrates include stainless steel foil, titanium foil, copper foil, aluminum foil, beryllium foil, a conductive oxide deposited over a polymer film (e.g., polyamide), a metal layer deposited over a polymer film, and other conductive structures and materials. In certain embodiments, a conductive substrate has a thickness of between about 2 mils and 50 mils (e.g., about 10 mils), with other thicknesses also within the scope. Generally, a substrate is sufficiently conductive such that a uniform and extensive distribution of interconnect wire network assembly wires is not needed for uniform current collection on this side. As such, a portion of the wire network assembly extending under the back side of one cell may be smaller than a corresponding portion extending over a front side of an adjacent cell. 
     As shown in  FIG. 1  and further explained below with reference to  FIG. 2 , interconnect wire network assemblies may include conductive portions, such as multiple individual wires, extending substantially parallel to each other. When installed into the module, conductive portions extend under photovoltaic cells and are illustrated with dashed line in  FIG. 1 . The other part of the conductive portions extends over front sides of adjacent cells and is shown with solid lines. When cells are spaced apart as shown in  FIG. 1 , a part of the conductive portions extends between the cells. In other embodiments, cells in the module may be adjacent to each other (e.g., have a minimal or no gap) or even overlap (sometimes referred to as a “shingle” arrangement). Interconnect wire network assemblies also have insulating carrier films, which allow various insulation schemes that in turn allow these various cell arrangements, as will be now described in more detail. 
       FIG. 2  is a schematic top view of an interconnect wire network assembly  200 , in accordance with certain embodiments. Assembly  200  includes conductive portions  202  and two carrier films (i.e., a first carrier film  204  and a second carrier film  206 ). Since these films  204 ,  206  are cut to a predetermined length, these films  204 ,  206  may be also referred to as carrier strips or decals. A portion of conductive portions  202  extends under first carrier film  204  from the top view perspective presented in  FIG. 2 . As such, this portion is shown with dashed lines. In certain embodiments, conductive portions  202  include multiple individual wires continuously extending between two edges (i.e., the first edge and the second edge) defined by ends of the wires along direction X. In certain embodiments, these wires extend substantially parallel to each other. Specifically, an angle between any pair of adjacent wires may be less than about 5° or, more specifically, less than about 1°. However, wires may extend in other directions and/or cross-over. 
     Substantially parallel wires are shown in  FIG. 2  and may be arranged and spaced apart along the length of assembly  200 , or direction Y. This arrangement may be characterized by a pitch  209 , which, for purposes of this document, is defined as a distance between the centers of two adjacent wires. The pitch determines the distance an electrical current travels through the conductive top layer of the cell prior to reaching more conductive wires of the interconnect wire network assembly  200 . Reducing the pitch increases the current collection characteristics of assembly  200 . However, a smaller pitch also decreases the useful surface area of the cell by covering the photovoltaic layer with non-transparent wires. In certain embodiments, pitch  209  is between about 2 millimeters and 5 millimeters (e.g., about 3.25 millimeters), although other distances may be used, as appropriate. 
     Conductive portions  202  are typically made from thin, highly conductive metal stock and may have round, flat, and other shapes. As mentioned above, conductive portions  202  are generally more conductive than the TCO layer and are used to improve current collection from the front surface of the cell. Examples of wire materials include copper, aluminum, nickel, chrome, or alloys thereof. In some embodiments, a nickel coated copper wire is used. In certain embodiments, the wire is 24 to 56 gauge, or in particular embodiments, 32 to 56 gauge (for example, 40 to 50 gauge). In specific embodiments, the wire has a gauge of 34, 36, 40, 42, 44, or 46. Additional wire examples are described in U.S. patent application Ser. No. 12/843,648, entitled “TEMPERATURE RESISTANT CURRENT COLLECTORS FOR THIN FILM PHOTOVOLTAIC CELLS,” filed Jul. 26, 2010, (Attorney Docket MSOLP039/IDF156), which is incorporated herein by reference in its entirety for purposes of describing additional wire examples. 
     Carrier films  204  and  206  are coupled to conductive portions  202  along two edges defined by the ends of conductive portions  202 , such as ends of wires shown in  FIG. 2 . These edges extend along the length of the assembly in direction Y and may be generally parallel to each other. Various positions of carrier films  204  and  206  with respect to these edges are explained below with reference to  FIGS. 3A, 3B, and 3C . As noted, during fabrication of a module, one carrier film is configured to attach wires  202  to a photovoltaic surface of one photovoltaic cell and may be referred to as a top carrier film or a top decal. Another carrier film is configured to attach wires  202  to a substrate surface of another photovoltaic cell and may be referred to as a bottom carrier film or a bottom decal. Either one of carrier films  204  and  206  can be a top carrier film, while another one can be a bottom carrier film. These designations are explained in more detail with reference to  FIG. 7 , which shows two photovoltaic cells interconnected using an interconnect wire network assembly. The attachments provided by the carrier films form electrical connections between conductive portions  202  and the photovoltaic and substrate surfaces of two cells. 
     Both top and bottom carrier films are made from electrically insulating materials. The top carrier film should also be substantially transparent so as to allow the sunlight to reach the photovoltaic layer. In certain embodiments, both carrier films are substantially transparent electrically insulating layers. Some examples of suitable carrier film materials include thermoplastic materials, such as polyethylene terephthalate (PET), ionomer resins (e.g., poly(ethylene-co-methacrylic acid)), polyamide, polyetheretherketone (PEEK), or combinations of these. One particular example is SURLYN®, available from E. I. du Pont de Nemours and Company in Wilmington, Del. In certain embodiments, one or both carrier films have a layered structure. For example, a carrier film may have three polymers layers, such as a co-extruded stack containing SURLYN®, PET, and another layer of SURLYN® (with the PET layer positioned in between the two SURLYN® layers). In certain embodiments, a suitable carrier may be a thermoplastic material or materials curable using ultra violet (UV) or other techniques. 
       FIG. 3A  is a schematic side view of the interconnect wire network assembly  200  depicted in  FIG. 2 , in accordance with certain embodiments. This side view further illustrates various arrangements of the assembly that may not be easily appreciated from the top view in  FIG. 2 . Specifically,  FIG. 3A  shows carrier films  204  and  206  attached to opposite sides of conductive portions  202 . With reference to direction Z, carrier film  204  is positioned on the top side of conductive portions  202 , while carrier film  206  is positioned on the bottom side of conductive portions  202 . This orientation does not necessarily correspond to carrier film  204  being a top carrier film in the module assembly. In this orientation and reference, the bottom surface of carrier film  204  may be an adhesive surface and used for securing carrier film  204  to conductive portions  202 . Furthermore, the same adhesive surface is used to secure carrier film  204  to the cell (e.g., to a photovoltaic surface if carrier film  204  is a top carrier film) after integration of assembly  200  into the module. Correspondingly, carrier film  206  has a top adhesive surface for securing carrier film  206  to conductive portions  202  and, after installation, to the cell (e.g., to a substrate surface if carrier film  206  is a bottom carrier film). Adhesion between the carrier films and conductive portions, during fabrication of the assembly, may be achieved by applying pressure between these components and/or heat to one or both components. These features are further described below with reference to  FIG. 4 . 
       FIG. 3A  illustrates carrier films  204  and  206  forming an overlap  208  in the middle portion of assembly  200 . This overlap may be used, in part, to prevent electrical shorts in the assembled module and for other purposes. At overlap  208 , carrier films  204  and  206  may be adhered to each other in the areas between adjacent conductive portions and outside of end conductive portions to provide additional structural integrity to assembly  200 . Further, conductive portions  202  are shown to extend past the outside edges of carrier films  204  and  206  (in direction X) and have exposed ends  205  and  207 . 
     Other arrangements of wires and carrier films in interconnect wire network assemblies are possible.  FIG. 3B  is a schematic side view of another assembly  300 , in accordance with different embodiments. Carrier films  304  and  306  extend past the wire ends (in direction X) and form insulating regions or flaps  305  and  307 . There may be a need to protect the ends of the wires to prevent their sharp corners from causing electrical shorts. Furthermore, carrier films  304  and  306  do not overlap in the middle portion of assembly  300 . Instead carrier films  304  and  306  form a gap  308  in that portion and expose a portion of wires  302 . This gap  308  may help to improve the flexibility of assembly  300  around this portion and may reduce the overall thickness of assembly  300 . 
       FIG. 3C  is a schematic side view of interconnect wire network assembly  310 , in accordance with different embodiments. Outside edges of carrier films  314  and  316  of this assembly coincide with the ends of wires  312 . This type of arrangement may be formed by cutting wires  312  together with carrier films  314  and  316  during fabrication of the assembly, as described below with reference to  FIG. 6B . Furthermore, carrier films  314  and  316  do not overlap in the middle portion of the assembly. Instead, the inside edges of carrier films  314  and  316  coincide. 
     In general, respective positions of the carrier films&#39; outside edges relative to the wires&#39; ends are independent from respective positions of the inside edges. Various combinations of these respective positions are not limited to the examples presented in  FIGS. 3A, 3B, and 3C  and described above. Other combinations are possible (e.g., extended outside edges (as shown in  FIG. 3B ) combined with overlapped inner edges (as shown in  FIG. 3A ), a middle gap (as shown in  FIG. 3B ) combined with exposed wire ends (as shown in  FIG. 3A ), and so on). 
     Returning to  FIG. 2 , carrier films  204  and  206  are shown to extend beyond end wires  202   a  and  202   b  in Y direction. These extensions form two side insulating regions  211   a  and  211   b , which may be referred to as insulating flaps. Insulating regions  211   a  and  211   b  do not have any conductive materials and may include only one or both carrier films. As such, insulating regions  211   a  and  211   b  can be used to insulate the edges of corresponding photovoltaic cells after fabrication of the module. For example, this insulation allows a closer arrangement of cells within a module along Y direction. It should be noted that only one carrier film may extend beyond end wires  202   a  and  202   b  to form insulating regions  211   a  and  211   b . In certain embodiments, there is not gap between two adjacent cells (not accounting portions of the interconnect assemblies attached to these cells) in this direction. The cells may even overlap in certain embodiments. Carrier films of the interconnect assemblies may be used to insulate edges of the two adjacent cells. For example, one portion of the carrier film may be attached to the front light incident side of the first cell, while another portion may extend outside of the first cell boundary and under the back side of the adjacent cell. This extension insulated the two adjacent edges of the cells with respect to each other. 
     In certain embodiments, conductive portions include individual wires such that each wire is electrically insulated from other wires. For example, the wires may extend substantially parallel to each other and/or do not touch each other. One having ordinary skills in the art would understand that such wires remain electrically insulated only until attachment of the assembly to a photovoltaic cell, during which the wires become interconnected by a front side, back side, or both. In other embodiments, wires may be interconnected by a strip of foil or other wires. The interconnection may be provided along one set of wires&#39; ends, similar to an example presented in  FIG. 1 . The interconnecting element (e.g., a foil strip) may then be used for connection to bus bars and/or other electrical components of the module. In certain embodiments, an interconnecting element may be used to enhance an electrical connection to a back side of the photovoltaic module. 
       FIG. 4  illustrates a flowchart corresponding to a process  400  of fabricating an interconnect wire network assembly, in accordance with certain embodiments. Process  400  may start with unwinding multiple individual wires from wire rolls or spools in operation  402 . In certain embodiments, multiple wires provided in operation  402  may be interconnected and provided as a woven mesh. However, it would be understood by one having ordinary skills in the art that other types of conductive portions may be used in addition or instead of individual wires. Various examples of wires are described above. The number of wires depends on a size of the assembly (and a photovoltaic cell) and a pitch between the wires. The wires may have different profiles (e.g., a round profile or a flat profile). 
     Process  400  may proceed with extending the wires along the same direction (i.e., “an unwinding direction”) in operation  404 . The wires may be substantially parallel during this operation and positioned at a predetermined distance from each other. In other embodiments, wires may be arranged in other configurations and may even overlap. During this operation, the wires may be arranged within substantially the same plane by, for example, applying a tension to the wires. In general, the multiple wires extended in this operation may be characterized as having a first surface and a second surface regardless of whether these surfaces are planar or not. These two surfaces are spaced apart by a cross-sectional dimension of the wires, such as wire diameters for round wires or wire thicknesses for flat wires. 
       FIG. 5  illustrates a schematic view of an apparatus  500  for fabricating an interconnect wire network assembly, in accordance with certain embodiments. Apparatus  500  includes multiple spools  502  providing multiple wires  504 . Wires  504  remain under tension provided by a rewind roller  508 , which is used for the winding of sub-assemblies. The pitch between wires  504  may be specific to the positioning of spools  502  and/or a guiding mechanism (not shown). 
     Returning to  FIG. 4 , process  400  then continues with applying one carrier film onto the first surface of the wires in operation  406  and applying another carrier film onto the second surface of the wires in operation  408 . These operations may be performed in parallel or in series. For example, one carrier film may be initially attached to the wires followed by a separate operation in which another carrier film is attached to the wires. In another example, both films are applied in the same operation. Edges of the two films can be aligned during this part of the process. Furthermore, in certain embodiments, one or both films are applied substantially perpendicular to the unwinding direction. Finally, this part of the process may also involve cutting the carrier films, if the films are supplied from continuous rolls. Overall, in certain embodiments, a product of this part of the process is a set of continuous wires with two strips of carrier film attached to the opposite sides of this set of wires. It should be noted that the operation of applying carrier film strips continues as wires are being unrolled and fed through the application area. 
     As shown in  FIG. 5 , apparatus  500  also includes two carrier film rolls  506   a  and  506   b , which supply the two films onto the two surfaces of the extended wires  504 . A mechanism (not shown) may be employed for grabbing free ends  507   a  and  507   b  of the carrier films to extend these films from rolls  506   a  and  506   b  and into position with respect to wires  504 . A cutting mechanism (not shown) may be employed for cutting the carrier films from the rolls  506   a  and  506   b  along a cutting line  509 . A roll-type or guillotine-type cutter can be used for these purposes. Cutting forms carrier film strips  510   a  and  510   b , which are carried by wires  504  to sub-assembly roll  508 . 
     In certain embodiments, applying a carrier film to the wires involves passing an electric current through at least a portion of the wires that is in contact with the carrier films. The electrical current heats this portion of the wires, which may help to adhere the carrier film to the wires. For example, two metal rollers may be put in temporary contact with wires in the post-application zone  512 . A predetermined voltage may be applied to the rollers at least during the contact period to drive current through the wires and heat the wires. Further, a pressure may be applied between wires  504  and carrier film strips  510   a  and  510   b  by, for example, passing a subassembly through nip rollers (e.g., heated rollers) in the post-application zone. 
     Returning to  FIG. 4 , process  400  may proceed with an optional operation  410 , during which continuous wires with carrier film films may be formed into a roll as, for example, shown in  FIG. 5 . This roll is considered to be a sub-assembly and may be stored prior to further processing, which involves unwinding the toll and cutting the wires to form interconnect wire network assemblies. Process  400  may then proceed with cutting wires across their length (e.g., in a direction substantially perpendicular to the wires) to form the interconnect wire network assembly in operation  412 . It should be noted that operation  412  may proceed without forming an intermediate subassembly (i.e., without an intermediate optional operation  410 ). A guillotine-type of cutter may be used for this purpose. Operation  412  may involve cutting only the wires in the areas free of the carrier films. An example of such an operation is shown in  FIG. 6A . Cutting lines  602  are depicted with heavy dashed lines (thin dashed lines correspond to the hidden edge of one carrier film strip). Cutting lines  602  pass through wires  504  but not through either one of carrier films  510   a  and  510   b . In other embodiments, operation  412  may involve cutting both the wires and one or more carrier films. An example of such an operation is shown in  FIG. 6B  where cut lines  604  go through both wires and initial carrier film strips  610   a  and  610   b . After cutting, carrier strip  610   a  is divided into new carrier strips  612   a  and  614   a , while carrier strip  610   b  is divided into new carrier strips  612   b  and  614   b . New carrier strips  612   a  and  612   b  together with a portion of wires  606  attached to these strips form an interconnect wire network assembly. 
       FIG. 7  illustrates a schematic side view of two photovoltaic cells  702  and  706  and an interconnect wire network assembly  710  electrically connecting these two cells, in accordance with certain embodiments. Assembly  710  includes wires  712  and two carrier films (i.e., top carrier film  714  and bottom carrier film  716 ). In certain embodiments, top carrier film  714  and bottom carrier film  716  are the same type of films (in terms of thickness and composition). The dimensions of top carrier film  714  and bottom carrier film  716  may be the same or different. Top carrier film  714  and bottom carrier film  716  are shown to overlap in the area  718 . However, other embodiments described above with reference to  FIGS. 3A, 3B, and 3C  are possible. Photovoltaic cell  702  includes a substrate  703  and a photovoltaic layer  704  positioned on a front surface of a substrate. Similarly, photovoltaic cell  706  includes a substrate  707  and a photovoltaic layer  708  positioned on a front surface of a substrate. A portion of bottom carrier film  716  extends beyond the edge of photovoltaic cell  702  and over photovoltaic layer  704  of this cell. This feature may be used to prevent short circuits between photovoltaic layer  704  and substrate  703  and caused by wires  712 . 
     Although the foregoing invention has been described in some detail for purposes of clarity of understanding, it will be apparent that certain changes and modifications may be practiced within the scope of the appended claims. It should be noted that there are many alternative ways of implementing the processes, systems and apparatus of the present invention. Accordingly, the present embodiments are to be considered as illustrative and not restrictive, and the invention is not to be limited to the details given herein.