WO2011011855A1

WO2011011855A1 - Method for interconnecting back contact solar cells and photovoltaic module employing same

Info

Publication number: WO2011011855A1
Application number: PCT/CA2009/001089
Authority: WO
Inventors: Leonid B. Rubin; Bram Sadlik
Original assignee: Day4 Energy Inc.
Priority date: 2009-07-31
Filing date: 2009-07-31
Publication date: 2011-02-03

Abstract

A back side contact photovoltaic (PV) cell apparatus including a crystalline silicon substrate having a front side for receiving light, a back side opposite said front side and one or more semiconductor junctions defined by one or more junction-forming regions of a first polarity and one or more junction-forming regions of a second polarity. The apparatus further includes a first plurality of exposed metal contact portions on said back side and spaced apart in two orthogonal directions. Furthermore, the apparatus includes a second plurality of exposed metal contact portions spaced apart in said two orthogonal directions, wherein substantially all of said columns of said second set are between adjacent columns of said first set, and whereby said adjacent columns of said exposed metal contact portions on said back side are of opposite polarity to facilitate connection of parallel spaced apart electrical conductors on an electrode on said back side.

Description

METHOD FOR INTERCONNECTING BACK CONTACT SOLAR CELLS AND PHOTOVOLTAIC MODULE EMPLOYING SAME

BACKGROUND OF THE INVENTION

1. Field of Invention

The present invention relates to photovoltaic cells and more particularly, to high-efficiency back contact photovoltaic cells.

2. Description of Related Art

A crystalline silicon photovoltaic (PV) cell typically has a front side surface that is operable to receive light and a back side surface opposite the front side surface. An emitter of the cell is normally just beneath the front side surface and is designed to receive as much light as possible. Normally, there are special electrical contacts on the front and back sides of the PV cell for connecting the PV cell to an external electrical circuit.

The electrical contacts on the front side surface are typically arranged as a plurality of parallel, spaced apart "fingers" or grid lines that extend across the entire front side surface. The fingers are typically formed by screen-printing a metal paste in a desired pattern on the front side surface and causing it to diffuse into the front side surface and leave a portion of the solidified paste on the surface, which acts as the fingers. Additional metal paste can be used to create bus bars perpendicular to the fingers and in contact therewith to collect electric current from the fingers. Bus bars are usually wider than the fingers in order to carry electric current from each of the fingers.

The electrical contacts and bus bars are opaque and thus, shade the emitter, from light. As a result, the effective emitter area that is available for light gathering is reduced. Since the fingers and bus bars shade the emitter, the area on the front side surface occupied by the fingers and bus bars is known as the "shading area". The shading area reduces the current-producing capacity of the PV cell. In modern solar cells, shading areas occupy about 6 to 10% of the available light-receiving surface area of the cell. Although silicon crystalline cells are produced in large volumes, there is an ongoing need to increase efficiency and to decrease production costs so that the use of photovoltaic energy can become more competitive. One method to increase efficiency is to decrease the shading area through the reduction of the metallization on the front side surface. By reducing the amount of metallization, the shading area is reduced, and the amount of metal paste diffused into the front side surface is reduced. The reduction of shading area results in an increase in area for reception of solar radiation, which increases the electric current and voltage of the PV cell. The reduction of the amount of metal diffused into the front side surface is advantageous since diffusion generally has a detrimental effect on the process of charge recombination in the PV cell. U.S. Patent No. 4,927,770, entitled "Method of Fabricating Back Surface Point

Contact Solar Cells", to Swanson, describes a back side contact PV cell without any conventional front side contact metallization. The Swanson patent describes several features of an interdigitated back side contact PV cell that are of interest, including an interdigitated emitter structure that is located on the back side of the PV cell and the use of the current-collecting contacts of both polarities on the back side of the PV cell, which removes the need for current-collecting metal contacts on the front side surface of the PV cell, and thus, minimizes recombination on the front side surface. The Swanson patent also describes the optimization of light trapping through the elimination of conventional shading and the introduction of efficient texturing.

The back side contact PV cell described in the Swanson patent is produced from high purity float-zone mono-crystalline n-type silicon material with a charge carrier lifetime greater than 1 ms. The minority carriers can thus approach the junction and current-collecting contacts of both polarities on the back side by diffusing from the illuminated front side surface through the entire thickness of the PV cell. The process of recombination on the front side surface is further reduced by the introduction of n+-doped and SiO₂ passivating layers on the front side surface.

The back side surface of the back side contact PV cell described in the Swanson patent includes interdigitated n+ and p+ parallel and narrow non- overlapping strips that lie between the opposing edges of the back side surface and are produced by sequential diffusion processes. An efficient electrical insulation is built between these strips to ensure high shunt resistance. The entire back side surface of the cell is covered by a SiO₂ layer to provide efficient back side passivation. Contacting holes are produced by way of precision alignment through the SiO₂ layer on the back side surface to the corresponding n+ and p+ strips. Another set of narrow metal contacts is printed by precision alignment along the corresponding contacting holes to provide the underlying n+ and p+ strips with current-collecting metal contacts. Two terminal bus bars are screen-printed on either edge of the back side surface so that one is connected to all n+ fingers and the other to all p+ fingers. These terminal bus bars can be used in the testing of the PV cells and also, to connect PV cells, in series, by means of special tabbing during the production of PV modules.

Using an interdigitated back-contact crystalline silicon PV cell a conversion efficiency of 23.4% has been achieved. Although this technology provides outstanding results, it suffers from several constraints. For example, the technology still requires special current-collecting fingers with high width to height aspect ratio to provide sufficiently high conductivity and relatively low power losses. In spite of this high aspect ratio, the length of the fingers is limited to about 125 mm. As well, the fingers are produced with expensive silver paste, which would substantially impacts production costs. Another type of back side contact solar cell is an Emitter Wrap-Through

(EWT) device. An EWT solar cell is similar to the above-mentioned back side contact solar cell and is described in US Patent No. 7,144,751 to Gee et al. However, the electrical connection between the emitter and the back side -A- surface involves electrically insulated holes that drive electric current from the front side surface to back side surface contacts connected to screen-printed fingers or grid lines. This technology allows the use of conventional solar grade silicon for PV cell production but still requires special current-collecting fingers, on the back side of the PV cell, having a high ratio of height to width in order to obtain a sufficiently high conductivity and relatively low power losses. In spite of this high aspect ratio, the length of the fingers is limited to 125 mm in highly efficient PV cells made from high quality crystalline silicon material. As well, the fingers are made from expensive silver paste, which can substantially impact production costs.

SUMMARY OF THE INVENTION

In accordance with one aspect of the invention, there is provided a back side contact photovoltaic (PV) cell apparatus including a crystalline silicon substrate having a front side for receiving light, a back side opposite the front side and one or more semiconductor junctions defined by one or more junction-forming regions of a first polarity and one or more junction-forming regions of a second polarity. The apparatus further includes a first plurality of exposed metal contact portions on the back side and spaced apart in two orthogonal directions across the back side to lie in a first set of rows and columns on the back side. The exposed metal contact portions of the first plurality are electrically connected on the substrate to the one or more junction-forming regions of the first polarity to associate the columns of the first set with the first polarity. The apparatus further includes a second plurality of exposed metal contact portions spaced apart in two orthogonal directions across the back side to lie in a second set of rows and columns on the back side and such that substantially all of the columns of the second set are between adjacent columns of the first set. The exposed metal contact portions of the second plurality are electrically connected on the substrate to the one or more junction-forming regions of the second polarity, such that the second set of columns of the exposed metal contact portions is associated with the second polarity, whereby the adjacent columns of the exposed metal contact portions on the back side are of opposite polarity to facilitate connection of parallel spaced apart electrical conductors on an electrode on the back side to respective columns to connect the PV cell to an electrical circuit. Substantially all of the rows of the second set are between adjacent rows of the first set such that the exposed metal contact portions of the second plurality are staggered in the two orthogonal directions, relative to the exposed metal contact portions of the first plurality. The first plurality of exposed metal contact portions may include portions of a first plurality of parallel spaced apart grid lines extending across the back side.

The second plurality of exposed metal contact portions may include portions of a second plurality of parallel spaced apart grid lines extending across the back side, the grid lines of the second plurality generally being between the grid lines of the first plurality.

The grid lines of the first and second pluralities of grid lines each may have a width of between about 50 microns to about 150 microns and a height of about 2 microns to about 15 microns.

The apparatus may further include a mask on the grid lines of the first and second pluralities of grid lines, the mask defining covered areas and uncovered areas of the grid lines of the first and second pluralities, the uncovered areas of the mask defining the rows and columns of the first and second sets, locations of the exposed metal contact portions being defined by locations of the uncovered areas of the mask.

The mask may include at least one of lacquer and epoxy.

The first plurality of exposed metal contact portions may include a first plurality of physically separate elongate-shaped metal segments arranged in a first plurality of parallel spaced apart lines extending across the back side, the lines of the first plurality defining the rows of the first set of rows and columns.

The second plurality of exposed metal contact portions may include a second plurality of physically separate elongate-shaped metal segments arranged in a second plurality of parallel spaced apart lines extending across the back side, the lines of the second plurality being generally between the lines of the first plurality and defining the rows of the second set of rows and columns. Each of the elongate-shaped metal segments of the first and second pluralities of lines may have a length of between about 1 mm to about 3 mm, a width of between about 50 microns to about 150 microns, a height of about 2 microns to about 15 microns, a spacing along the lines approximately equal to the length of the segments and a separation distance to an adjacent line of about 0.5mm to about 3mm.

The apparatus may include an electrode extending across the back side of the first PV cell. The electrode may comprise an electrically insulating film having a surface and an adhesive layer on the surface. The apparatus may further include a first set of electrical conductors embedded into the adhesive layer in parallel spaced apart relation, wherein the electrical conductors of the first set are spaced apart and are physically and electrically connected to the exposed metal contact portions in respective the columns associated with the first polarity on the first PV cell. The apparatus may further include a second set of electrical conductors embedded into the adhesive layer in parallel spaced apart relation, the conductors of the second set being generally interdigitated with the conductors of the first set and wherein the conductors of the second set are spaced apart and are physically and electrically connected to the exposed metal contact portions in respective the columns associated with the second polarity on the first PV cell. The first set of electrical conductors may act as a first terminal for the first PV cell and the second set of conductors acts as a second terminal for the first PV cell. In accordance with another aspect of the invention, there is provided an apparatus including the first and second PV cells of the type described above and further including an electrode extending across the back side of the first and second PV cells. The electrode may include an electrically insulating film having a surface and an adhesive layer on the surface. The electrode may further include a first set of electrical conductors embedded into the adhesive layer in parallel spaced apart relation. The electrical conductors may be spaced apart and may be physically and electrically connected to the exposed metal contact portions in respective the columns associated with the first polarity on the first PV cell. The electrode may further include a second set of electrical conductors embedded into the adhesive layer in parallel spaced apart relation, the conductors of the second set being generally interdigitated with the conductors of the first set. The conductors of the second set may be spaced apart and may be physically and electrically connected to the exposed metal contact portions in respective columns associated with the second polarity on the first PV cell and the electrical conductors of the second set may be further physically and electrically connected to the exposed metal contact portions in respective columns associated with the first polarity on the second PV cell to connect the first and second PV cells in series. The electrode may further include a final set of electrical conductors embedded into the adhesive layer in parallel spaced apart relation, the electrical conductors of the final set being physically and electrically connected to the exposed metal contact portions in respective columns associated with the second polarity on the second PV cell. The first and final sets of electrical conductors may act as positive and negative terminals of the string.

In accordance with another aspect of the invention, there is provided an apparatus including first, second and third PV cells of the type described above and further including an electrode extending across the back side of the first, second and third PV cells. The electrode may include an electrically insulating film having a surface, an adhesive layer on the surface and a first set of electrical conductors embedded into the adhesive layer in parallel spaced apart relation. The electrical conductors may be spaced apart and may be physically and electrically connected to the exposed metal contact portions in respective columns associated with the first polarity on the first PV cell. The electrode may further include a second set of electrical conductors embedded into the adhesive layer in parallel spaced apart relation, the conductors of the second set being generally interdigitated with the conductors of the first set. The conductors of the second set may be spaced apart and may be physically and electrically connected to the exposed metal contact portions in respective columns associated with the second polarity on the first PV cell and the electrical conductors of the second set may be further physically and electrically connected to the exposed metal contact portions in respective columns associated with the first polarity on the second PV cell to connect the first and second PV cells in series. The electrode may further include a third set of electrical conductors embedded into the adhesive layer in parallel spaced apart relation, the electrical conductors of the third set being physically and electrically connected to the exposed metal contact portions in respective columns associated with the second polarity on the second PV cell and the third set of electrical conductors being physically and electrically connected to the exposed metal contact portions in respective columns associated with the first polarity on the third PV cell. The electrode may further include a final set of electrical conductors embedded into the adhesive layer in parallel spaced apart relation, the electrical conductors of the final set being physically and electrically connected to the exposed metal contact portions in respective columns associated with the second polarity on said third PV cell. The first and final sets of electrical conductors may act as positive and negative terminals of the string.

In accordance with another aspect of the invention, there is provided a method of making a back side contact photovoltaic (PV) cell. The method involves forming a first plurality of exposed metal contact portions on a back side of a crystalline silicon substrate having a front side opposite the back side and one or more semiconductor junctions defined by one or more junction-forming regions of a first polarity and one or more junction-forming regions of a second polarity. The exposed metal contact portions are spaced apart in two orthogonal directions across the back side to lie in a first set of rows and columns on the back side, the exposed metal contact portions of the first plurality being electrically connected on the substrate to one or more junction-forming regions of the first polarity to associate the columns of the first set with the first polarity. The method further involves forming a second plurality of exposed metal contact portions spaced apart in two orthogonal directions across the back side to lie in a second set of rows and columns on the back side and such that substantially all of the columns of the second set are between adjacent columns of the first set, and such that the exposed metal contact portions of the second plurality are electrically connected on the substrate to one or more junction-forming regions of the second polarity, such that the second set of columns of the exposed metal contact portions is associated with the second polarity, and such that adjacent columns of the exposed metal contact portions on the back side are of opposite polarity, to facilitate connection of parallel spaced apart electrical conductors on an electrode on the back side to respective columns to connect the PV cell to an electrical circuit.

Forming at least one of the first and second pluralities of exposed metal contact portions may involve causing substantially all of the rows of the second set to be between adjacent rows of the first set such that the exposed metal contact portions of the second plurality are staggered in two orthogonal directions relative to the exposed metal contact portions of the first plurality.

Forming the first plurality of exposed metal contact portions may involve exposing portions of a first plurality of parallel spaced apart grid lines extending across the back side.

Forming the second plurality of exposed metal contact portions may involve exposing portions of a second plurality of parallel spaced apart grid lines extending across the back side, the grid lines of the second plurality generally being between the grid lines of the first plurality.

Forming the first and second pluralities of exposed metal contact portions may involve forming a mask on the grid lines of the first and second pluralities of grid lines, the mask defining covered areas and uncovered areas of the grid lines of the first and second pluralities, the uncovered areas of the mask defining the rows and columns of the first and second sets, locations of the exposed metal contact portions being defined by locations of the uncovered areas of said mask.

Forming the mask may involve applying at least one of lacquer and epoxy to the back side.

Forming the first plurality of exposed metal contact portions may involve forming a first plurality of physically separate elongate-shaped metal segments arranged in a first plurality of parallel spaced apart lines extending across the back side, the lines of the first plurality defining the rows of the first set of rows and columns. Forming the second plurality of exposed metal contact portions may involve forming a second plurality of physically separate elongate-shaped metal segments arranged in a second plurality of parallel spaced apart lines extending across the back side, the lines of the second plurality being generally between the lines of the first plurality and defining the rows of the second set of rows and columns.

Forming the elongate-shaped metal segments of the first and second pluralities of lines may involve forming the elongate-shaped metal segments of the first and second pluralities of lines such that the elongate-shaped metal segments may have a length of between about 1 mm to about 3 mm, a width of between about 50 microns to about 150 microns, a height of about 2 microns to about 15 microns, a spacing along the lines approximately equal to the length of the segments, and a separation distance to an adjacent line of about 0.5mm to about 3mm.

Connecting a first PV cell to an electrical circuit may involve causing an adhesive on an electrically insulating film to adhere the film to the back side in a position such that a first set of electrical conductors embedded into the adhesive layer in parallel spaced apart relation is physically and electrically connected to the exposed metal contact portions in respective columns associated with the first polarity on the first PV cell and such that a second set of electrical conductors embedded into the adhesive layer in parallel spaced apart relation and generally interdigitated with the conductors of the first set may be physically and electrically connected to the exposed metal contact portions in respective columns associated with the second polarity on the first PV cell. The first set of electrical conductors may act as a first terminal for the first PV cell and the second set of electrical conductors may act as a second terminal for the first PV cell.

In accordance with another aspect of the invention, there is provided a method of making an electrode for interconnecting a plurality of back contact PV cells in a series string. The method involves punching parallel spaced apart electrical conductors embedded in an adhesive layer on an electrically insulating film in odd and even positions across the film, to form odd and even punch lines extending laterally across the film, at longitudinally spaced apart intervals along the film to interrupt the conductors and thereby create a plurality of sets of conductors along the film, and to define at least one PV cell receiving area between adjacent odd and even punch lines. The sets of conductors includes a first set of conductors associated with odd positions across the film, the first set of conductors extending from a first end of the film to a first PV cell receiving area of the at least one PV cell receiving area. The method further involves an end set of conductors associated with even positions across the film, the end set of conductors extending from a second end of the film to a final PV cell receiving area of the at least one PV cell receiving area.

The at least one PV cell receiving area may comprise only one PV cell receiving area and the first PV cell receiving area and the final PV cell receiving area may be one and the same.

Punching may include punching a sufficient number of odd and even punch lines to define a plurality of interdigitated sets of conductors between the first set and the end set of conductors and to define at least one intermediate PV cell receiving area between the first PV cell receiving area and the last PV cell receiving area. In accordance with another aspect of the invention, there is provided a method of making a string of PV cells. The method involves laying PV cells in respective ones of the PV cell receiving areas of an electrode as described above, such that columns of exposed electrical contact portions associated with a first polarity on back sides of the PV cells are aligned and in contact with the conductors in the odd positions and such that columns of exposed electrical contact portions associated with a second polarity on back sides of the PV cells are aligned and in contact with the conductors in the even positions. The method further involves causing the adhesive on the electrode to adhere to the back sides of the PV cells to secure the electrode in place on the back sides of the PV cells.

In accordance with another aspect of the invention, there is provided an electrode for interconnecting a plurality of back contact PV cells in a series string. The electrode includes an electrically insulating film having a surface with an adhesive layer thereon, and first and second opposite ends. The electrode further includes a first set of electrical conductors embedded into the adhesive layer in parallel spaced apart relation at a spacing corresponding to a spacing of columns of exposed metal contact portions associated with a common polarity of at least one junction-forming region on the PV cells. The first set of electrical conductors has a length longer than a length of a first one of the PV cells in the series string. The electrode further includes a plurality sets of electrical conductors embedded into the adhesive layer in parallel spaced apart relation and disposed longitudinally along the film, at a spacing across the film corresponding to the spacing of columns of exposed metal contact portions associated with the common polarity of the at least one junction-forming region on the PV cells and interdigitated with conductors of adjacent sets of conductors, wherein respective sets of conductors have a length corresponding to a length of about two of the PV cells in the series string and wherein at least one of the sets of conductors is in a position on the film longitudinally adjacent the first set of conductors. The electrode further includes a final set of electrical conductors embedded into the adhesive layer in parallel spaced apart relation at a spacing corresponding to the spacing of columns of exposed metal contact portions associated with the common polarity of the at least one junction-forming region on the PV cells wherein the conductors of the final set of electrical conductors have a length longer than a length of a final one of the PV cells in the series string. The first set of conductors and the final set of conductors are positioned at the first and second opposite ends, respectively, of the film to facilitate acting as first and second terminals of the series string.

Devices made according to the embodiments described herein can provide for a decrease in the production cost of back contact PV cells because less silver paste is used as a result of the elimination of current collectors at opposite edges of the PV cell that collect current from the grid lines and due to the ability to reduce the size of the grid lines.

For example, it is generally known that power losses due to conductor resistivity are proportional to the square of the length of the conductor. In conventional back contact PV cells the length of the current collecting fingers is normally about 125 mm for a 5-inch square cell or about 156 mm for a 6- inch square cell. Use of the methods and devices described herein allows reducing this length to less than 3 mm, which typically corresponds to about half distance between the conductors on the electrode. This reduction in length significantly reduces the amount of silver paste required to make the grid lines and improves the efficiency of the PV cell. This reduction in length of the grid lines can reduce power loss resulting from the grid lines by about 125²/3²=1736 times. Using the devices and methods described herein production costs of PV cell modules can be reduced because the electrodes can be pre-manufactured and simply adhered to a plurality of suitably oriented adjacent PV cells such that the electrical conductors on the electrode are in physical and electrical contact with the pluralities of exposed metal contact portions on all PV cells in a string, as described below. The electrodes can be connected to adjacent electrodes of adjacent strings and the entire set of strings can be laminated in a conventional vacuum lamination process. Conventional tabbing and stringing processes that involve conventional soldering are eliminated and this eliminates the risks associated with localized heating which can result in PV cell breakage.

The invention described herein provides improved ways of gathering current from back contact PV cells to enhance efficiency, simplify the series interconnection of these cells and reduce manufacturing costs.

Other aspects and features of the present invention will become apparent to those ordinarily skilled in the art upon review of the following description of specific embodiments of the invention in conjunction with the accompanying figures.

BRIEF DESCRIPTION OF THE DRAWINGS

In drawings which illustrate embodiments of the invention,

Figure 1 is a perspective view of a back contact photovoltaic (PV) cell substrate bearing a mask, in accordance with one embodiment of the invention.

Figure 2 is a cross-sectional view of a prior art back contact PV cell according to US Patent No. 7,468, 485.

Figure 3 is a cross-sectional view of an emitter wrap-through back contact PV cell according to US Patent No. 7,144,751.

Figure 4 is a perspective view of a back side of the substrate shown in

Figure 1 without the mask. Figure 5 is a perspective view of a back side of a substrate prepared in accordance with an alternative embodiment of the invention to include physically separated exposed metal contact portions.

Figure 6 is a perspective view of a PV module comprising one PV cell and one electrode.

Figure 7 is a top plan view of a PV module comprising 2 PV cells and an electrode connecting them together in series.

Figure 8 is a top plan view of a PV module comprising 3 PV cells and an electrode connecting the 3 PV cells together in series. Figure 9 is a top plan view of an electrode according to one embodiment of the invention.

Figure 10 is a schematic diagram of a process for making the electrode shown in Figure 9.

Figure 11 is a top plan view of a PV module comprising 2 strings employing the PV cells and electrodes described herein.

Figure 12 is a fragmented top plan view of an interconnection method used to interconnect the strings of PV cells shown in Figure 11 together in series.

DETAILED DESCRIPTION

Referring to Figure 1, a back side contact photovoltaic (PV) cell apparatus is shown generally at 10. The apparatus 10 comprises a crystalline silicon substrate 12 having a front side 14 for receiving light, a back side 16 opposite the front side and one or more semiconductor junctions defined by one or more junction-forming regions of a first polarity and one or more junction- forming regions of a second polarity. For example, referring to Figure 2, the PV cell apparatus may be of the type described in US Patent No 7,468,485 issued December 23, 2008 to Swanson, which describes a back side contact solar cell having a plurality of semiconductor junctions defined by junction- forming regions 18 and 20 of first and second polarities designated as n+ and p+ that define junctions 22. Referring to Figure 3, as another example, US Patent No 7,144,751 to Gee et al. describes emitter wrap-through (EWT) back contact solar cells that have a junction 24 defined by an interface of junction- forming regions 26 and 28 described as n+ and p+ semiconductor material.

The back contact solar cells shown in Figures 2 and 3 each have a plurality of grid lines or fingers extending across the back side 16 in a manner similar to that shown in Figure 4 in which alternate grid lines or fingers are connected to semiconductor junction-forming regions of opposite polarity. For example, a first plurality of grid lines 30, 32, 34 etc. is connected to n+ junction-forming regions and a second plurality of grid lines 31 , 33, 35 etc. is connected to p+ junction-forming regions. In the case of the PV cell shown in Figure 2, the first plurality set of grid lines 30, 32, 34 may be formed in a back-end process similar to that disclosed in US Patent No. 7,339,110 by employing a seed layer on the substrate to connect the grid lines of the first plurality to the junction-forming region of the first polarity such as n+. The second plurality of grid lines 31 , 33, 35 may be formed in the same way as the first plurality, but are connected to the p+ type junction-forming region by a seed layer on the substrate.

In the case of the EWT cell shown in Figure 3, the grid lines 30, 32, 34 of the first plurality are connected to the n+ junction-forming region by a heavily doped n++ tube 56 on the substrate and the grid lines 31 , 33, 35 of the second plurality are connected to the p+ junction-forming region by heavily doped p++ regions 64 on the substrate. The grid lines of the first and second pluralities of grid lines each have a width of between about 50 microns to about 150 microns, a height of about 2 microns to about 15 microns and a lateral spacing of between about 1 mm to 5 mm. Normally, all of the grid lines connected to the n+ junction-forming regions are electrically connected together by bus bars or additional metallization at one side margin of the substrate and all of the grid lines connected to the p+ junction-forming regions are electrically connected together by bus bars or additional metallization at the other side margin of the substrate. In the embodiment according to the invention described herein, this additional metallization on the side margins of the substrate is deliberately omitted and the first and second pluralities of grid lines or fingers 30, 32, 34 and 31 , 33, 35 are provided as shown in Figure 4, that is, each grid line is physically separate and not connected to any other grid lines or bus bars or additional metallization on the back side 16. This reduces the amount of material used for metallization and hence improves back side passivation and reduces the cost of metallization and the deleterious effect of diffusion associated with metallization.

Using a back contact PV cell having first and second pluralities of grid lines as shown in Figure 4, referring back to Figure 1 , in accordance with the embodiment described herein, a mask 40 is formed on the back side 16, over all of the grid lines including grid lines 30, 32, 34 and 31 , 33, 35 of the first and second pluralities of grid lines. The mask 40 may be formed by any of various means including the application of epoxy or lacquer or other appropriate conforming coating material. The mask 40 may be applied by screen-printing, extrusion, ink jet printing, aerosol printing or any other suitable method. The mask 40 defines covered areas and uncovered areas of the grid lines. The uncovered areas are arranged in rows and columns wherein the rows extend in a first direction 41 along respective grid lines and the columns extend in a second direction 43 orthogonal to the first direction. A first set 42 of rows and columns of uncovered areas is depicted by circles and a second set 44 of rows and columns of uncovered areas is depicted by squares. The actual shape of the uncovered areas need not be circular or square. The use of circles and squares in the drawing is merely intended to distinguish uncovered areas of the first and second sets 42 and 44 respectively. The actual shape of the uncovered areas may be rectangular, for example, and the uncovered areas along the rows may be spaced apart by between about 1 mm to about 5 mm, for example. The uncovered areas are spaced apart along the columns by about 0.5 mm to about 3 mm.

Still referring to Figure 1 , as a result of the mask 40 and the first set 42 of uncovered areas, the first set of uncovered areas leaves exposed a first plurality of exposed metal contact portions of the first plurality of grid lines 30, 32, 34. One of such exposed metal contact portions is shown at 46. Because of the arrangement of the first set 42 of uncovered areas provided by the mask 40, the exposed metal contact portions (such as 46) of the first plurality are spaced apart in two orthogonal directions namely the first and second directions 41 and 43 across the back side 16 to lie in a first set of rows 52 and columns 54 on the back side. Since the exposed metal contact portions (such as 46) of the first set 42 of rows and columns are exposed portions of the first plurality of grid lines 30, 32, 34 they are thus electrically connected on the substrate 12 to the one or more junction-forming regions of the first polarity, in this embodiment the n+ polarity, and thus associate the rows 52 and columns 54 of the first set with the first polarity.

The second set 44 of uncovered areas leaves exposed a second plurality of exposed metal contact portions of the second set of grid lines 31 , 33, 35. One of such exposed metal contact portions is shown at 58. Because of the arrangement of the second set of uncovered areas provided by the mask 40, the second plurality of exposed metal contact portions (such as 58) of the second plurality are spaced apart in the same two orthogonal directions 41 and 43 across the back side 16 to lie in a second set of rows 60 and columns 62 such that substantially all of the columns 62 of the second set are between adjacent columns 54 of the first set. Only an end one of the columns 62 for example, is not between adjacent columns of the first set and generally, this is what is meant by "substantially all" in this paragraph. The exposed metal contact portions (such as 58) of the second set of rows and columns 60 and 62 are exposed portions of the second plurality of grid lines 31 , 33, 35 and are thus electrically connected on the substrate 12 to the one or more junction-forming regions of the second polarity, in this embodiment, the p+ polarity.

Thus, the exposed metal contact portions (such as 58) in the columns 62 of the second set are associated with the second polarity of junction-forming regions in the cell. Effectively, the mask 40 provides uncovered areas in which columns of exposed metal contact portions (such as 46) associated with the first polarity (n+) are interdigitated with columns of exposed metal contact portions (such as 58) associated with the second polarity (p+). As a result, adjacent columns 54 and 62 of the exposed metal contact portions 46 and 58 on the back side 16 are of opposite polarity. Desirably, the column of exposed metal contact portions adjacent a first side of the substrate is associated with the first polarity and the column of exposed metal contact portions adjacent a second side opposite the first side is associated with the second polarity. This facilitates connection of parallel spaced apart electrical conductors on an electrode to respective columns to facilitate connection of the PV cell to an electrical circuit as will be described below.

In the embodiment shown in Figure 1 , substantially all of the rows 60 of the second set of rows and columns are between adjacent rows 52 of the first set such that the exposed metal contact portions (such as 58) of the second plurality are staggered in the two orthogonal directions 41 and 43 relative to the exposed metal contact portions (such as 46) of the first plurality. The exposed metal contact portions of the first and second pluralities of exposed metal contact portions (such as 46 and 58) are thus arranged in a checkerboard pattern across the back side 16.

Referring to Figure 5, an apparatus according to a second embodiment of the invention includes a PV cell substrate 70 of the type described in connection with Figures 1 and 4, with the exception that the grid lines shown in Figures 1 and 4 are eliminated and instead are replaced with first and second pluralities 72 and 74 of physically separate exposed metal contact portions 76. The first plurality 72 of exposed metal contact portions 76 includes a first plurality of physically separate elongate-shaped metal contact segments arranged in a first plurality of parallel spaced apart lines extending across the back side, defining a first set of rows 78 of separate elongate-shaped metal contact segments.

The second plurality 74 of exposed metal contact portions includes a second plurality of physically separate elongate-shaped metal contact segments arranged in a second plurality of parallel spaced apart lines extending across the back side 16 defining a second set of rows 80 of separate elongate- shaped metal contact segments. The separate exposed metal contact portions 76 of the second plurality 74 are in parallel spaced apart rows 80 interdigitated with the rows 78 of the first plurality 72 of exposed metal contact portions and are staggered relative to the exposed metal contact portions in the rows 78 of the first plurality and thus the exposed metal contact portions of the first and second pluralities 72 and 74 form a checkerboard pattern across the back side 16 of the substrate 70.

Thus, the first and second pluralities 72 and 74 of separate exposed metal contact portions also define first and second interdigitated parallel spaced apart columns 82 and 84 of separate exposed metal contact portions. As before, the first and second columns 82 and 84 are electrically connected to and thereby associated with respective junction-forming regions of a semiconductor junction or semiconductor junctions of the substrate 70 and thus are associated with first and second polarities respectively of the junction-forming regions. More particularly, the first set of columns 82 is associated with junction-forming regions of the first polarity such as n+, for example, and the second set of columns 84 is associated with junction- forming regions of the second polarity such as p+, for example. Each of the separate elongate-shaped contact metal segments of the first and second pluralities has a length of between about 1 mm to about 5 mm, a width of between about 50 microns to about 150 microns, a height of about 2 microns to about 15 microns and a spacing along the rows approximately equal to the length of the segments and a spacing to the next adjacent row (of opposite polarity) is about 0.5 mm to 3 mm.

Where the substrate 70 has the form of the substrate shown in Figure 2, for example, the separate elongate-shaped metal contact segments of the first and second pluralities 72 and 74 may be formed on the back side by screen- printing physically separated segments of electrical contact paste instead of continuous lines (seen in Figure 4) and then diffusing the paste into the back side to make contact with strips of alternating polarity on the back side of the substrate 70. Other methods of applying the electrical contact paste in physically separated segments may alternatively be employed instead of screen-printing.

Where the substrate 70 has the form of the substrate shown in Figure 3, for example, the separate elongate-shaped metal contact segments of the first and second pluralities 72 and 74 may be formed on the back side by fabricating the substrate such that the heavily doped n++ tubes 56 are in the above indicated row and column pattern associated with the first plurality 72 of exposed metal contact portions 76 and such that the heavily doped p++ regions 64 are in the above indicated row and column pattern associated with the second plurality 74 of exposed metal contact portions. Physically separate line segments are then formed on respective heavily doped n++ tubes 56 and p++ regions 64 in the same manner as the grid lines except they are not continuous lines of the type seen in Figure 4. Whether the mask 40 as described in connection with Figure 1 is used or whether the exposed metal contact portions 76 are physically separate exposed metal contacts as shown in Figure 5, the result is first and second pluralities of exposed metal contact portions arranged in rows and columns, wherein the rows and columns of the second plurality are staggered relative to the rows and columns of the first plurality and the exposed metal contact portions in columns of the first plurality are associated with at least one junction-forming region of a first polarity and the exposed metal contact portions in columns of the second plurality are associated with at least one junction-forming region of a second polarity on the substrate 70.

Referring to Figure 6, a PV string apparatus comprising a first PV cell apparatus 10 of the type shown in Figure 1 and an electrode 100 extending across the back side 16 of the first PV cell apparatus 10 is shown. As described above, the first PV cell apparatus 10 has the first set of rows and columns 52 and 54 of exposed metal contact portions and also has the second set of rows and columns 60 and 62 of exposed metal contact portions. The electrode 100 comprises an electrically insulating film 102 having an underside surface 104 with an adhesive layer 106 thereon and a first set of electrical conductors shown generally at 108 embedded into the adhesive layer 106 in parallel spaced apart relation. The electrical conductors have portions that protrude from the adhesive layer and which are coated with a low melting point alloy which enables them to be heated and pressed onto the exposed metal contact portions to essentially become soldered to the exposed metal contact portions and make ohmic contact therewith.

In this embodiment the first set 108 of conductors includes conductors 110, 112, 114 and 116 spaced apart and extending over the back side 16, in physical and electrical contact with exposed metal contact portions in the columns 54 associated with the first plurality of exposed metal contact portions. A second set of electrical conductors shown generally at 120 is embedded into the adhesive layer, also in parallel spaced apart relation. The conductors of the second set 120 include conductors 122, 124, 126 and 128 which are generally interdigitated with the conductors 110, 112, 114 and 116 of the first set 108. The conductors 122, 124, 126 and 128 of the second set 120 are spaced apart and are physically and electrically connected to the exposed metal contact portions in respective columns 62 associated with the second plurality of exposed metal contact portions.

In the embodiment shown, the electrically insulating film 102 has a first end portion 101, a mid-portion 103 and a second end portion 105. The first set

108 of electrical conductors extends across the first end portion 101 and the mid-portion 103 and the second set 120 of electrical conductors extends across the mid-portion 103 and the second end portion 105. The first and second sets 108 and 120 of electrical conductors are interdigitated at the mid- portion 103. The conductors 110, 112, 114 and 116 of the first set 108 have distal ends 130, 132, 134 and 136 that are connected to a metallic foil bus bar

138 such as tinned copper for example, disposed at a distal end edge of the first end portion 101 and connect all of the conductors of the first set together. Thus, the first set 108 of electrical conductors 110, 112, 114 and 116 and bus bar 138 act as a first terminal for the PV cell apparatus 10, the first terminal

139 being electrically connected through the conductors to the junction- forming regions of the first polarity of the PV cell apparatus 10.

Similarly, the electrical conductors 122, 124, 126 and 128 of the second set 120 of conductors have distal end portions 140, 142, 144 and 148 connected to a second metallic foil bus bar 146 disposed at a distal end edge of the second end portion 105. The second metallic foil bus bar 146 connects all of the conductors 122, 124, 126 and 128 of the second set 120 together to thereby act as a second terminal 147 for the first PV cell apparatus 10, connected to the regions of the second polarity in the PV cell 10. Thus, the first terminal 139 may act as a positive terminal for the PV cell 10 and the second terminal 147 may act as a negative terminal, the positive terminal being more positive, in electrical potential when the PV cell 10 is exposed to light, than the negative terminal. Thus, the first and second sets 108 and 120 of conductors cooperate with rows associated with respective common pluralities of junction-forming regions of the PV cell apparatus 10 to provide electrical connection thereto in a convenient manner facilitating electrical connection of the PV cell to an external electrical circuit through the positive and negative terminals 139 and 147 respectively.

Referring to Figure 7, a PV string apparatus according to another embodiment of the invention is shown generally at 150. The apparatus 150 includes a first

PV cell 152 of the type described above in connection with Figures 1 or 5 and a second PV cell 154 of the same type. The first and second PV cells 152 and 154 need not be identical. For example, the first PV cell 152 may be of the type described in connection with Figure 1 and the second PV cell 154 may be of the type described in connection with Figure 5.

The first PV cell 152 has first and second sets 156 and 158 of exposed metal contact portions arranged in first and second sets of rows and columns 160, 162 and 164, 166. All of the columns 162 of the first set are associated with a junction-forming region of a first polarity such as n+ for example and all of the columns 166 of the second set are associated with a junction-forming region of a second polarity such as p+ for example on the first PV cell 152.

The second PV cell 154 has first and second sets 176 and 178 of exposed metal contact portions arranged in first and second sets of rows and columns

180, 184 and 182, 186. All of the columns 184 of the first set are associated with a junction-forming region of the first polarity (such as n+ for example) and all of the columns 186 of the second set 178 are associated with a junction- forming region of the second polarity (such as p+ for example). It should be noted that the first and second sets 176 and 178 of exposed metal contact portions of the second PV cell 154 are associated with junction-forming regions of opposite polarity than the junction-forming regions of the first PV cell 152. Since the first and second PV cells 152, 154 will generally be formed such that the exposed metal contact portions have the same spacing in the first and second directions and such that in one orientation the first set

156 of columns 162 has a column 157 adjacent a right hand side edge of the PV cell and the second set 158 of columns 166 has a column 159 adjacent a left hand side of the PV cell. This enables the second PV cell 154 to have an orientation in which it is rotated 180 degrees relative to the first PV cell 152 to cause the columns 166 of the second set 158 on the first PV cell 152 to be automatically aligned with columns 184 of the first set 176 on the second PV cell 154.

The PV string 150 further includes an electrode 192 similar to that described in connection with Figure 6 in which the electrode comprises a film 194 having a first end portion 196, a first mid-portion 198, a second mid-portion 200 and a second end portion 202. The film 194 has a surface 204 facing the back sides 16 of the first and second PV cells 152 and 154 and the surface has an adhesive 206 spread over the entire surface.

The electrode 192 further includes a plurality of parallel spaced apart electrical conductors embedded in the adhesive 206 and these conductors include a first set 208 of electrical conductors spaced apart to align with columns 162 of exposed metal contact portions associated with the first polarity (n+) on the first PV cell 152. This first set 208 of electrical conductors extends across the first end portion 196 and the first mid-portion 198. The electrode 192 further includes a second set 210 of electrical conductors spaced apart to align with columns 166 of exposed metal contact portions associated with the second polarity (p+) on the first PV cell 152. This second set 210 of electrical conductors extends across the first mid-portion 198 and the second mid-portion 200 and connects the exposed metal contact portions in columns 166 associated with the second polarity (p+) on the first PV cell

152 to the exposed metal contact portions of columns 184 associated with the first polarity n+ on the second PV cell 154.

The electrode 192 further includes a third set 212 of electrical conductors spaced apart to align with columns 186 of exposed electrical contact portions associated with the second polarity (p+) on the second PV cell 154. This third set 212 of electrical conductors extends across the second mid-portion 200 and the second end portion 202. It will be appreciated that the first set 208 of electrical conductors is electrically connected to the exposed metal contact portions in respective columns 162 associated with the first polarity in the first PV cell 152 and extend from the first end portion to a point no further than the first PV cell.

The second set 210 of electrical conductors is connected to exposed metal contact portions in respective columns 166 associated with the second polarity on the first PV cell 152 and to the exposed metal contact portions in respective columns 184 associated with the first polarity on the second PV cell 154 and thus connect the first and second PV cells together in series.

The third set 212 of electrical conductors is electrically connected to the exposed metal contact portions in respective columns 186 associated with the second polarity on the second PV cell 154 and extend to the second end portion 202 of the electrode 192.

The electrode 192 further includes first and second bus bars 220 and 222, which in this embodiment include lengths of metal foil secured to the film 194 by the adhesive 206, for example. End portions of the first and third sets 208 and 212 of electrical conductors are connected to first and second bus bars

220 and 222 respectively. Thus, the first and second bus bars 220 and 222 act as first and second terminals or positive and negative terminals of the PV string 150 and enable connection of the PV module to an external electrical circuit.

Referring to Figure 8, a PV string apparatus according to another embodiment of the invention is shown generally at 250. The apparatus 250 includes the first and second PV cells 152 and 154 shown in Figure 7 and includes a third PV cell shown generally at 252. The third PV cell 252 has first and second sets 254 and 256 of exposed metal contact portions arranged in first and second sets of rows and columns 258, 260 and 262, 264. All of the columns 260 of the first set 254 are associated with a junction-forming region of a first polarity such as n+, for example, and all of the columns 264 of the second set 256 are associated with a junction-forming region of a second polarity such as p+, for example. It should be noted that the first and second sets 254 and 256 of exposed metal contact portions of the third PV cell 252 are associated with junction-forming regions of opposite polarity to the junction-forming regions of the second PV cell 154 and of the same polarity as the first PV cell 152. This can be achieved, for example, by simply rotating the third PV cell 252 to align columns 186 of exposed metal contact portions in rows associated with the second polarity on the second PV cell 152 with exposed metal contact portions in columns 260 associated with the first polarity on the third PV cell 252, for example.

The apparatus 250 further includes an electrode 270 comprising an electrically insulating film 271 having a portion 272 the same as the electrode 192 shown in Figure 7, including the first end portion 196, the first mid-portion 198 and the second mid-portion 200. The electrode 270 further includes a third mid-portion 273 extending over the third PV cell 252 and a terminating portion 275. The electrode 270 further includes the first, second and third sets 208, 210 and 212, of electrical conductors shown in Figure 7, however in this embodiment, the electrical conductors of the third set 212 are connected to respective exposed metal contact portions in columns 260 associated with the first polarity on the third PV cell 252 and extend along the film 271 from the second PV cell 154 to no further than the third PV cell 252. The third set 212 of electrical conductors thus connects the second and third PV cells 154 and 252 in series.

The electrode 270 further includes a fourth set 274 of electrical conductors spaced apart to align with columns 264 of exposed metal contact portions associated with the second polarity (p+) on the third PV cell 252. This fourth set 274 of electrical conductors extends across the third mid-portion 273 and the terminating portion 275.

It will be appreciated that the first set 208 of electrical conductors is electrically connected to the exposed metal contact portions in respective columns 162 associated with the first polarity on the first PV cell 152 and extend from the first end portion 196 to a point no further than the first PV cell. The second set 210 of electrical conductors is connected to exposed metal contact portions in respective columns 166 associated with the second polarity on the first PV cell 152 and to the exposed metal contact portions in respective columns 184 associated with the first polarity on the second PV cell 154 and thus connect the first and second PV cells together, in series.

The third set 212 of electrical conductors is electrically connected to the exposed metal contact portions in respective columns 186 associated with the second polarity on the second PV cell 154 and extend across the third PV cell

252 to connect to exposed metal contact portions in columns 260 associated with the first polarity on the third PV cell and thus connect the second and third PV cells 154 and 252 in series. The fourth set 274 of electrical conductors is electrically connected to the exposed metal contact portions in columns 264 associated with the second polarity on the third PV cell 252 and extend to the terminating portion 275.

The electrode 270 further includes first and second bus bars 280 and 282, which in this embodiment include lengths of metal foil as described above in connection with Figure 7. End portions of the first and fourth sets 208 and

274 of electrical conductors are connected to the first and second bus bars

280 and 282 respectively. Thus, the first and second bus bars 280 and 282 act as first and second terminals or positive and negative terminals of the PV module apparatus 250 and enable connection of the PV module to an external electrical circuit.

It should be appreciated that PV strings of one, two and three PV cells have been described in Figures 6, 7 and 8 and that by using an electrode of a suitable length, any number of PV cells can be connected together in series simply by using an electrode of suitable length and including sets of conductors to provide a first terminal portion and to connect respective adjacent pairs of PV cells together by connecting the exposed metal contact portions in columns associated with a second polarity on a PV cell with exposed metal contact portions in columns associated with a first polarity on a subsequent PV cell and to include a second terminal portion. The PV module can then be connected to an external electrical circuit using the first and second terminal portions.

Referring to Figure 9 an electrode for interconnecting a plurality of back contact PV cells in a series string in a more general sense is shown generally at 300. Generally the electrode 300 includes an electrically insulating film 302 having a surface 304 with an adhesive layer 306 thereon and first and second opposite ends 308 and 310. A first set of electrical conductors 312 is embedded into the adhesive layer 306 in parallel spaced apart relation at a spacing corresponding to a spacing of columns of exposed metal contact portions associated with a first common polarity of at least one junction forming region on the PV cells. The first set of electrical conductors 312 has a length 314 longer than a length 316 of a first one of the PV cells in this series string.

The electrode 300 also includes at least one set 321 of electrical conductors embedded into the adhesive layer 306 in parallel spaced apart relation and disposed longitudinally along the film 302 at a spacing across the film corresponding to the spacing of columns of exposed metal contact portions associated with a second common polarity of the at least one junction forming region on the PV cells and interdigitated with conductors of adjacent sets of conductors, one of which is shown at 326. Portions of the conductors are coated with a low melting point alloy and protrude from the adhesive layer

306.

Respective sets of conductors have a length 322 corresponding to a length 324 of about two of the PV cells in the series string. At least one of the sets

(326) of conductors is in a position on the film 302 longitudinally adjacent the first set of conductors 312. The electrode 300 also includes a final set 328 of electrical conductors embedded into the adhesive layer 306 in parallel spaced apart relation at a spacing corresponding to the spacing of columns of exposed metal contact portions associated with the second common polarity of the at least one junction forming region on the PV cells. The conductors of the final set 328 have a length 330 longer than a length 332 of a final one of the PV cells in the series string. The first set of conductors 312 and the final set of conductors 328 are positioned at the first and second opposite ends 308 and 310 of the film 302 to facilitate acting as first and second electrical terminals of the series string. It will be appreciated that a plurality of any number of intermediate sets of conductors can be provided in the above- indicated interdigitated and longitudinally spaced apart fashion to create an electrode for use in connecting together a series string of any number of PV cells.

Referring to Figures 10(a) - 10(c) a method of making an electrode such as the electrode shown in Figure 9 is shown generally at 340. Referring to

Figure 10(a) the method involves forming a base shown generally at 342 by embedding a plurality of parallel spaced apart wires 344 into an adhesive layer 346 on an electrically insulating film 348 such that portions 350 of the wires protrude from the adhesive layer. The wires are spaced apart by a distance corresponding to the distance between adjacent columns on the PV cells on which the electrode is intended to be used.

For the electrically insulating film 348 and the adhesive layer, a wide range of materials may be used as described in United States Patent No. 7,432,438 to Rubin et al issued October 7, 2008.

The wires 344 are coated with a low melting point alloy and extend from a first end 352 of the film 348 to a second end 354 of the film. The alloy may be any of a plurality of common solders or specially developed solders as described in United States Patent No. 7,432,438, issued October 7, 2008 to Rubin et al.

First and second metallic foil strips 356 and 358 are disposed at the first and second ends 352 and 354 respectively and lie over and in contact with the wires 344 to act as first and second bus bars or terminals. The length of the film from the first end 352 to the second end 354 is set according to the number of PV cells and the spacing between them over which the finished electrode is intended to span to connect the PV cells together into a series string. In the embodiment shown, the electrode has a length (L) that may be determined according to the relation:

L= n^* (s+w)+a^*s, Where: n is the number of PV cells the electrode is intended to connect, s is the spacing between PV cells,

w is the width of one PV cell; and

a is a number between 2 and 4. The variable "a" in the relation provides a convenient way to allow for extra length at opposite ends of the film 348 to allow the bus bars to be located away from the PV cells at opposite ends of the string to facilitate connection to adjacent strings or to external circuits. Of course a greater number would allow for a greater length of film at opposite ends of the film 348 and a smaller number would allow for a lesser length of film at opposite ends of the film.

Referring to Figure 10(b) after the base 342 has been prepared as described in connection with Figure 10(a), the base has first, second, third, fourth, fifth, sixth, etc. parallel wires. More generally it has odd numbered wires 360, i.e. first, third, fifth etc. and even numbered wires 362 i.e. second, fourth, sixth, etc. In Figure 10(b) the base 342 is subjected to a punching operation in which the film 348 is perforated simultaneously by a plurality of spaced apart punches 364 on a set of spaced part punch heads including odd and even heads 366 and 368. On the odd punch heads 366, the punches are spaced apart to align with the odd numbered wires 360 and on the even punch heads

368, the punches are spaced apart to align with the even numbered wires 362. The odd and even punch heads 366 and 368 are connected together by an actuator 370 which simultaneously drives all of the odd and even punch heads through the wires 344 and film 348 at the same time, in one operation, to create a plurality of odd and even spaced apart punch lines shown generally at 372 and 374 respectively. The odd and even punch heads 366 and 368 and hence the punch lines 372 and 374 are spaced apart relative to each other by a distance that may be calculated according to the relation: s+w

Where: s is the spacing between PV cells; and

w is the width of one PV cell.

The odd and even punch lines 372 and 374 define PV cell receiving areas therebetween and define the different sets of wires described above. In this embodiment the PV cell receiving areas include a first PV call receiving area 371 a plurality of intermediate PV cell receiving areas 373 and a final PV cell receiving area 375. The odd punch lines 372 are spaced apart from each other along the film 348 at a distance defined by 2(s+w) and the even punch lines 374 are spaced apart along the film at a distance also defined by 2(s+w) but are interposed at locations between the odd punch lines. In addition, the sizes of the odd and even punch heads 366 and 368 are the same and in this embodiment are circular with a diameter slightly larger than the spacing between adjacent PV cells to ensure that there is no risk of unintentionally permitting any wire from a set of wires from contacting a PV cell that it is not intended to contact. In particular, the ends of the wires cut by the punch are sufficiently spaced apart from edges of adjacent PV cells to avoid inadvertent electrical shunting across their edges when heating and laminating.

Before the punching operation is initiated, the film 348 is aligned relative to the punch heads, such that the set of odd and even punch heads 366 and 368 is approximately centered longitudinally along the film 348. The film 348 is desirably punched in a face-up orientation in which the adhesive side of the film is facing toward the punch heads 366 and 368 when the punching operation is initiated. The punching operation effectively punches the plurality of parallel spaced apart electrical conductors in this case wires 344 embedded in the adhesive layer 346 on the electrically insulating film 348 in odd and even positions across the film, to form odd and even punch lines 372 and 374 extending laterally across the film, at longitudinally spaced apart intervals along the film to interrupt the conductors and thereby create a plurality of sets of conductors along the film, and to define at least one PV cell receiving area 375 between adjacent odd and even punch lines. No matter how long the electrode is, it always includes a first set of conductors (360) associated with odd positions across the film, the first set of conductors extending from the first end 352 of the film to the first PV cell receiving area 371 of the at least one PV cell receiving area and an end set of conductors (362) associated with even positions across the film, the end set of conductors extending from a second end of the film 354 to a final PV cell receiving area 375 of the at least one PV cell receiving area.

Where the electrode is to be used to make electrical connection to only one PV cell the at least one PV cell receiving area on the electrode will include only one PV cell receiving area as shown at 377 in Figure 6 and this PV cell receiving area will essentially act as the first PV cell receiving area and the final PV cell receiving area. The first and last PV cell receiving areas are thus one and the same in the case where the electrode is intended to connect to only one PV cell.

For an electrode to be used with a plurality of PV cells as shown in Figures 9 and 10(a)-(c), a sufficient number of odd and even punch lines is made in the electrode to define a plurality of interdigitated sets of conductors between the first set and the end set of conductors and to define at least one intermediate PV cell receiving area 373 between the first PV cell receiving area 371 and the last PV cell receiving area 375. The number of PV cell receiving areas depends on the number of PV cells the electrode is intended to connect together. Referring to Figure 10(c), after the odd and even punch lines 372 and 374 have been formed in the film 348 and wires 344, and with the adhesive side of the film facing upwardly, PV cells 380, 382, 384, 386 and 388 are placed on the film, back side down, in alternately opposite orientations in the PV cell receiving areas so that the first and second pluralities of exposed contact portions described above are aligned and in physical and electrical contact with respective sets of wires and such that the adhesive secures the film to the back sides of the PV cells.

The PV cells 380-388 are thus physically and electrically connected together into a series string by the electrode and may be placed and connected to adjacent strings of similar type in a PV module and laminated by heating and pressing, which further secures the adhesive and melts the low melting point alloy to solder sets of wires to respective PV cells, thereby ensuring a good solid electrical connection of the wires to the exposed metal contact points and bus bars.

Referring to Figure 11 , a PV module comprising two series strings employing the electrodes of the type described in connection with Figure 9 and made according to the process shown in Figure 10 are disclosed generally at 400. The PV module includes a first string 402 and a second string 404. Each of the strings has a first and last PV cell in the string 406 and 408 and has a respective positive and negative terminal 412 and 414, each comprised of a metallic foil strip 411 and 413 respectively. The first and second strings 402 and 404 are identical except the second string 404 is oriented at 180 degrees relative to the first string and is placed side by side in parallel spaced apart relation. The negative terminal 414 of the first string 402 is connected to the positive terminal 412 of the second string by a small piece of metal foil such as shown at 420 by soldering the metal foil to the metallic foil strip at the ends of the first and second strings 402 and 404 respectively. The first and second strings 402 and 404 are thus connected in series and the positive terminal 412 of the first string acts as the positive terminal for the entire module. Similarly, the negative terminal 414 of the second string 404 acts as the negative terminal of the entire module.

Referring to Figure 12, as an alternative to the additional metal foil (420 shown in Figure 11), the metallic foil strips 411 and 413 at the ends of the first and second strings 402 and 404 respectively may be extended such that portions 422 and 424 thereof extend past respective adjacent edges 426 and 428 of the first and second strings 402 and 404 and therefore overlap. A low melting point alloy may be applied between the overlapping portions 422 and 424 such that the first and second strings 402 and 404 can be laminated between protective sheets by heating and pressing, using conventional methods, and such heating and pressing can cause the low melting point alloy between the overlapping portions 422 and 424 to melt and solder the overlapping portions 422 and 424 together. This simplifies PV module production.

In all cases described herein the PV cells are of the back contact type and thus the electrode and electrical conductors associated therewith are on the back sides of the PV cells used in the PV module and therefore impose no shading on the front sides of the PV cells.

While specific embodiments of the invention have been described and illustrated, such embodiments should be considered illustrative of the invention only and not as limiting the invention as construed in accordance with the accompanying claims.

Claims

What is claimed is:

1. A back side contact photovoltaic (PV) cell apparatus comprising: a crystalline silicon substrate having a front side for receiving light, a back side opposite said front side and one or more semiconductor junctions defined by one or more junction- forming regions of a first polarity and one or more junction- forming regions of a second polarity; a first plurality of exposed metal contact portions on said back side and spaced apart in two orthogonal directions across said back side to lie in a first set of rows and columns on said back side, said exposed metal contact portions of said first plurality being electrically connected on said substrate to said one or more junction-forming regions of said first polarity to associate said columns of said first set with said first polarity; and a second plurality of exposed metal contact portions spaced apart in said two orthogonal directions across said back side to lie in a second set of rows and columns on said back side and such that substantially all of said columns of said second set are between adjacent columns of said first set, and wherein said exposed metal contact portions of said second plurality are electrically connected on said substrate to said one or more junction-forming regions of said second polarity, such that said second set of columns of said exposed metal contact portions is associated with said second polarity, whereby said adjacent columns of said exposed metal contact portions on said back side are of opposite polarity to facilitate connection of parallel spaced apart electrical conductors on an electrode on said back side to respective columns to connect said PV cell to an electrical circuit.

2. The apparatus of claim 1 wherein substantially all of said rows of said second set are between adjacent rows of said first set such that said exposed metal contact portions of said second plurality are staggered in said two orthogonal directions relative to said exposed metal contact portions of said first plurality.

3. The apparatus of claim 2 wherein said first plurality of exposed metal contact portions includes portions of a first plurality of parallel spaced apart grid lines extending across said back side.

4. The apparatus of claim 3 wherein said second plurality of exposed metal contact portions includes portions of a second plurality of parallel spaced apart grid lines extending across said back side, said grid lines of said second plurality generally being between said grid lines of said first plurality.

5. The apparatus of claim 4 wherein said grid lines of said first and second pluralities of grid lines each have a width of between about 50 microns to about 150 microns and a height of about 2 microns to about

15 microns.

6. The apparatus of claim 4 or 5 further comprising a mask on said grid lines of said first and second pluralities of grid lines, said mask defining covered areas and uncovered areas of said grid lines of said first and second pluralities, said uncovered areas of said mask defining said rows and columns of said first and second sets, locations of said exposed metal contact portions being defined by locations of said uncovered areas of said mask.

7. The apparatus of claim 6 wherein said mask includes at least one of lacquer and epoxy.

8. The apparatus of claim 2 wherein said first plurality of exposed metal contact portions includes a first plurality of physically separate elongate-shaped metal segments arranged in a first plurality of parallel spaced apart lines extending across said back side, said lines of said first plurality defining said rows of said first set of rows and columns.

9. The apparatus of claim 8 wherein said second plurality of exposed metal contact portions includes a second plurality of physically separate elongate-shaped metal segments arranged in a second plurality of parallel spaced apart lines extending across said back side, said lines of said second plurality being generally between said lines of said first plurality and defining said rows of said second set of rows and columns.

10. The apparatus of claim 9 wherein each of said elongate-shaped metal segments of said first and second pluralities of lines have a length of between about 1 mm to about 3 mm, a width of between about 50 microns to about 150 microns, a height of about 2 microns to about 15 microns, a spacing along said lines approximately equal to the length of said segments and a separation distance to an adjacent line of about

0.5mm to about 3mm.

11. A PV apparatus comprising a first PV cell according to any one of claims 1 to 10 further comprising an electrode extending across said back side of said first PV cell, the electrode comprising an electrically insulating film having a surface, an adhesive layer on said surface of said film; and: a first set of electrical conductors embedded into the adhesive layer in parallel spaced apart relation, wherein said electrical conductors are spaced apart and are physically and electrically connected to said exposed metal contact portions in respective said columns associated with said first polarity on said first PV cell; and a second set of electrical conductors embedded into the adhesive layer in parallel spaced apart relation, said conductors of said second set being generally interdigitated with said conductors of said first set, wherein said conductors of said second set are spaced apart and are physically and electrically connected to said exposed metal contact portions in respective said columns associated with said second polarity on said first

PV cell; wherein said first set of electrical conductors acts as a first terminal for said first PV cell and said second set of conductors acts as a second terminal for said first PV cell.

12. A PV apparatus comprising first and second adjacent PV cells according to any one of claims 1 to 10 and further comprising: an electrode extending across said back sides of said first and second

PV cells, the electrode comprising: an electrically insulating film having a surface; an adhesive layer on said surface; a first set of electrical conductors embedded into the adhesive layer in parallel spaced apart relation, wherein said electrical conductors are spaced apart and are physically and electrically connected to said exposed metal contact portions in respective said columns associated with said first polarity on said first PV cell; and a second set of electrical conductors embedded into the adhesive layer in parallel spaced apart relation, said conductors of said second set being generally interdigitated with said conductors of said first set, wherein said conductors of said second set are spaced apart and are physically and electrically connected to said exposed metal contact portions in respective said columns associated with said second polarity on said first PV cell and wherein said electrical conductors of said second set are further physically and electrically connected to said exposed metal contact portions in respective columns associated with said first polarity on said second PV cell to connect said first and second PV cells in series; and a final set of electrical conductors embedded into the adhesive layer in parallel spaced apart relation, said electrical conductors of said final set being physically and electrically connected to said exposed metal contact portions in respective columns associated with said second polarity on said second PV cell; wherein said first and final sets of electrical conductors act as positive and negative terminals of the string.

13. A PV apparatus comprising first, second and third adjacent PV cells according to any one of claims 1 to 10 and further comprising: an electrode extending across said back side of said first, second and third PV cells, the electrode comprising: an electrically insulating film having a surface; an adhesive layer on said surface; a first set of electrical conductors embedded into the adhesive layer in parallel spaced apart relation, wherein said electrical conductors are spaced apart and are physically and electrically connected to said exposed metal contact portions in respective said columns associated with said first polarity on said first PV cell; and a second set of electrical conductors embedded into the adhesive layer in parallel spaced apart relation, said conductors of said second set being generally interdigitated with said conductors of said first set, wherein said conductors of said second set are spaced apart and are physically and electrically connected to said exposed metal contact portions in respective said columns associated with said second polarity on said first PV cell and wherein said electrical conductors of said second set are further physically and electrically connected to said exposed metal contact portions in respective columns associated with said first polarity on said second PV cell to connect said first and second PV cells in series; and a third set of electrical conductors embedded into the adhesive layer in parallel spaced apart relation, said electrical conductors of said third set being physically and electrically connected to said exposed metal contact portions in respective columns associated with said second polarity on said second PV cell and said third set of electrical conductors being physically and electrically connected to said exposed metal contact portions in respective columns associated with said first polarity on said third PV cell; and a final set of electrical conductors embedded into the adhesive layer in parallel spaced apart relation, said electrical conductors of said final set being physically and electrically connected to said exposed metal contact portions in respective columns associated with said second polarity on said third PV cell; wherein said first and final sets of electrical conductors act as positive and negative terminals of the string.

14. A method of making a back side contact photovoltaic (PV) cell, the method comprising: forming a first plurality of exposed metal contact portions on a back side of a crystalline silicon substrate having a front side opposite said back side and one or more semiconductor junctions defined by one or more junction-forming regions of a first polarity and one or more junction-forming regions of a second polarity, said exposed metal contact portions being spaced apart in two orthogonal directions across said back side to lie in a first set of rows and columns on said back side, said exposed metal contact portions of said first plurality being electrically connected on said substrate to said one or more junction-forming regions of said first polarity to associate said columns of said first set with said first polarity; and forming a second plurality of exposed metal contact portions spaced apart in said two orthogonal directions across said back side to lie in a second set of rows and columns on said back side and such that substantially all of said columns of said second set are between adjacent columns of said first set, and such that said exposed metal contact portions of said second plurality are electrically connected on said substrate to said one or more junction-forming regions of said second polarity, such that said second set of columns of said exposed metal contact portions is associated with said second polarity, and such that said adjacent columns of said exposed metal contact portions on said back side are of opposite polarity to facilitate connection of parallel spaced apart electrical conductors on an electrode on said back side to respective columns to connect said PV cell to an electrical circuit.

15. The method of claim 14 wherein forming at least one of said first and second pluralities of exposed metal contact portions comprises causing substantially all of said rows of said second set to be between adjacent rows of said first set such that said exposed metal contact portions of said second plurality are staggered in said two orthogonal directions relative to said exposed metal contact portions of said first plurality.

16. The method of claim 15 wherein forming said first plurality of exposed metal contact portions includes exposing portions of a first plurality of parallel spaced apart grid lines extending across said back side.

17. The method of claim 16 wherein forming said second plurality of exposed metal contact portions includes exposing portions of a second plurality of parallel spaced apart grid lines extending across said back side, said grid lines of said second plurality generally being between said grid lines of said first plurality.

18. The method of claim 17 wherein forming said first and second pluralities of exposed metal contact portions comprises forming a mask on said grid lines of said first and second pluralities of grid lines, said mask defining covered areas and uncovered areas of said grid lines of said first and second pluralities, said uncovered areas of said mask defining said rows and columns of said first and second sets, locations of said exposed metal contact portions being defined by locations of said uncovered areas of said mask.

19. The method of claim 18 wherein forming said mask includes applying at least one of lacquer and epoxy to said back side.

20. The method of claim 15 wherein forming said first plurality of exposed metal contact portions includes forming a first plurality of physically separate elongate-shaped metal segments arranged in a first plurality of parallel spaced apart lines extending across said back side, said lines of said first plurality defining said rows of said first set of rows and columns.

21. The method of claim 20 wherein forming said second plurality of exposed metal contact portions includes forming a second plurality of physically separate elongate-shaped metal segments arranged in a second plurality of parallel spaced apart lines extending across said back side, said lines of said second plurality being generally between said lines of said first plurality and defining said rows of said second set of rows and columns.

22. The method of claim 21 wherein forming said elongate-shaped metal segments of said first and second pluralities of lines comprises forming said elongate-shaped metal segments of said first and second pluralities of lines such that said elongate-shaped metal segments have a length of between about 1 mm to about 3 mm, a width of between about 50 microns to about 150 microns, a height of about 2 microns to about 15 microns, a spacing along said lines approximately equal to the length of said segments, and a separation distance to an adjacent line of about 0.5mm to about 3mm.

23. A method of connecting a first PV cell according to any one of claims 1 to 9 to an electrical circuit, the method comprising causing an adhesive on an electrically insulating film to adhere said film to said back side in a position such that: a first set of electrical conductors embedded into the adhesive layer in parallel spaced apart relation are physically and electrically connected to said exposed metal contact portions in respective said columns associated with said first polarity on said first PV cell; and such that a second set of electrical conductors embedded into the adhesive layer in parallel spaced apart relation and generally interdigitated with said conductors of said first set are physically and electrically connected to said exposed metal contact portions in respective said columns associated with said second polarity on said first PV cell; wherein said first set of electrical conductors is operable to act as a first terminal for said first PV cell and said second set of electrical conductors is operable to act as a second terminal for said first PV cell.

24. A method of making an electrode for interconnecting a plurality of back contact PV cells in a series string, the method comprising: punching parallel spaced apart electrical conductors embedded in an adhesive layer on an electrically insulating film in odd and even positions across said film, to form odd and even punch lines extending laterally across the film, at longitudinally spaced apart intervals along said film to interrupt said conductors and thereby create a plurality of sets of conductors along said film, and to define at least one PV cell receiving area between adjacent said odd and even punch lines, said sets including: a first set of conductors associated with odd positions across said film, said first set of conductors extending from a first end of said film to a first PV cell receiving area of said at least one PV cell receiving area; an end set of conductors associated with even positions across said film, said end set of conductors extending from a second end of said film to a final PV cell receiving area of said at least one PV cell receiving area.

25. The method of claim 24 wherein said at least one PV cell receiving area comprises only one PV cell receiving area and wherein said first PV cell receiving area and said final PV cell receiving area are one and the same.

26. The method of claim 25 wherein said punching comprises punching a sufficient number of odd and even punch lines to define a plurality of interdigitated sets of conductors between said first set and said end set of conductors and to define at least one intermediate PV cell receiving area between said first PV cell receiving area and said last PV cell receiving area.

27. A method of making a string of PV cells the method comprising the method of any one of claims 24-26 and further comprising: laying PV cells in respective ones of said PV cell receiving areas such that columns of exposed electrical contact portions associated with a first polarity on back sides of said PV cells are aligned an in contact with said conductors in said odd positions and such that columns of exposed electrical contact portions associated with a second polarity are aligned and in contact with said conductors in said even positions; and causing said adhesive to adhere to said back sides.

28. An electrode for interconnecting a plurality of back contact PV cells in a series string, the electrode comprising: an electrically insulating film having a surface with an adhesive layer thereon, and first and second opposite ends; a first set of electrical conductors embedded into said adhesive layer in parallel spaced apart relation at a spacing corresponding to a spacing of columns of exposed metal contact portions associated with a common polarity of at least one junction-forming region on the PV cells and said first set of electrical conductors to having a length longer than a length of a first one of the PV cells in the series string; a plurality sets of electrical conductors embedded into said adhesive layer in parallel spaced apart relation and disposed longitudinally along said film, at a spacing across said film corresponding to said spacing of columns of exposed metal contact portions associated with said common polarity of said at least one junction-forming region on the PV cells and interdigitated with conductors of adjacent said sets of conductors, wherein respective said sets of conductors have a length corresponding to a length of two of said PV cells in the series string and wherein at least one of said sets of conductors is in a position on said film longitudinally adjacent said first set of conductors; a final set of electrical conductors embedded into said adhesive layer in parallel spaced apart relation at a spacing corresponding to said spacing of columns of exposed metal contact portions associated with said common polarity of said at least one junction-forming region on said PV cells wherein said conductors of said final set of electrical conductors have a length longer than a length of a final one of said PV cells in the series string; wherein said first set of conductors and said final set of conductors are positioned at said first and second opposite ends respectively of said film to facilitate acting as first and second terminals of said series string.