Field The present invention relates to a process for assembling a solar cell. A particular embodiment relates to a process for assembling a solar cell from flexible

materials that may, for example, be placed in a rolled configuration after assembly.

Background

Solar cells are available in various forms from rigid structures including silicon wafers, inorganic electrodes and glass housings, through to more flexible structures including organic materials and polymers. There is considerable interest in solar cells having flexible structures on account of the broad range of possible applications, such as military applications in which troops are positioned in remote locations without external power sources, domestic house hold applications, and from highly technical applications such as space craft

applications through to recreational activities such as used in tents.

The development of flexible solar active materials has created a demand for new processes to assist in the assembly of solar cells. The present invention has been devised with this demand in mind. SUMMARY

An embodiment of the present invention relates to a process of assembling a solar cell including a first film that has first solar active material preapplied thereon that can be provided in a first film roll, and a second film that has a second solar active material preapplied thereon that can be provided in a second film roll, wherein the process includes the steps of:

conveying a continuous length of the first film from the first film roll toward a first nip formed between two rollers ;

conveying a continuous length of the second film from the second film roll toward the first nip;

extruding an adhesive from an extrusion head at an elevated temperature range onto at least one of the first solar active material and the second solar active

material; and

pressing together the first and second films by passing the first and second films through the first nip so as to bond together the first and second solar active materials with the adhesive and form a flexible web product containing a solar cell assembly.

Another embodiment of the present invention relates to a solar cell comprising a first film that has first solar active material preapplied thereon and a second film that has a second solar active material preapplied thereon, wherein the first and second solar active materials are bonded together by an adhesive to form a flexible web product containing a solar cell assembly. Ideally, the inner faces of the first and second films have the first and second solar active materials thereon respectively and ideally the inner faces of the first and second films face toward each other. Outer faces of the web product are ideally formed by outer faces of the first and second films .

In this specification, the web product may also be known as the web assembly.

In an embodiment, the process includes orienting inner faces of the first and second films, having solar active materials applied thereon, to face toward each other.

The step of pressing the first and second films together may include operably moving the two rollers to adjust the pressure applied to the films .

In an embodiment, the adhesive material may be a hot melt polymeric material.

Although it is possible that the adhesive may be a thermoset polymer, ideally the adhesive is a thermoplastic polymer .

Examples of the suitable thermoplastic polymers include polypropylene, polyethylene, acrylics and so forth.

In another embodiment, the adhesive may include a monomer and an initiator or catalyst that react in a

polymerisation reaction to form a polymeric material.

Polymerisation may occur during at least one of: prior to extrusion of the adhesive from the extrusion head, during extrusion of the adhesive from the extrusion, or after extrusion of the adhesive from the extrusion head.

Examples of suitable monomers include propylene, ethylene, methacrylates and acrylates. Examples of suitable

initiators include azo compounds such as

azobisisobutyronitrile, peroxides such as di-tert-butyl peroxide and peroxydisulfate salts . Examples of catalysts include Ziegler-Natta catalysts.

In any event, the adhesive may bond the first and second films, including the first and second solar active materials by means of the physical bonding. The adhesive may also bond by means of chemical bonding in addition to, or alternatively to, physical bonding. The term "elevated temperature" or variants thereof can embrace any temperature range above ambient temperature .

In one example, the elevated temperature at which the adhesive may be extruded from the extrusion head may be at a temperature in the range of 200 to 350°C. The adhesive may be extruded from the extrusion head in a stream which cools by heat transfer to the atmosphere to a temperature in the range of 100 to 200° C, and preferably in the range of 125 to 175°C at the point at which the adhesive contacts the first or second films.

In one embodiment, the adhesive may be a conductive adhesive .

In another embodiment, the adhesive may be a non- conductive adhesive and in which case, the process may include forming electrical bridges between the first an> second solar active material of the first and second films .

In one embodiment, the step of forming electrical bridges may include pinching the web product so as to displace the non-conductive adhesive in sections between the first and second solar active materials so as to allow electrical interconnection therebetween. The electrical bridges in this instance may be provided by direct contact between the first and second solar active materials.

In another embodiment, the step of forming electrical bridges may include punching the web product and inserting a conductive material interconnecting the first and second solar active materials.

In the event that the step of punching breaks or forms an opening in the first and second films, the process may also include applying a sealant to the break or opening after insertion of a conductive material.

Forming the electrical bridges may be carried out whilst the non-conductive adhesive is at an elevated temperature, for example, immediately after or possibly during the step of pressing the first and second films together.

Forming the electrical bridges may also be carried out disjunctively with the formation of the web assembly after a time period. For example, in the situation in which forming the electrical bridges includes pinching the web assembly, forming the electrical bridges may include heating the web assembly to an elevated temperature in order to soften the adhesive. This option is particularly available in the instance where the adhesive is a

thermoplastic material such as polypropylene.

In any event, forming the electrical bridges may be carried out in any subsequent converting stages, including die cutting and so forth.

The steps of conveying the first and second films may be performed without contacting the inner faces of the first and second films. In addition, the step of pressing the first and second films together may be performed without contacting the inner faces of the first and second films.

It will be appreciated that the term "without contacting the inner faces of the first and second films" embraces the inner faces of the first and second films not

contacting solid equipment such as rollers, screens or guiding wires. An advantage this provides is that the process can be carried out without potentially disrupting the solar active material, thereby reducing the risk of the process interfering with the reliability of the solar cell assembly.

The process may include a step of joining the first film to a flexible medium including the following: a) applying an adhesive between the first film and the flexible medium; and

b) pressing the first film and flexible medium

together with the adhesive therebetween.

The step of joining the first film to the flexible medium may be a preliminary step that occurs prior to the first and second films being joined together, that is prior to formation of the solar cell assembly.

The step of joining the first film to the flexible medium may occur after formation of the solar cell assembly.

The flexible medium may be any suitable substrate

depending on the intended application, including for example, any one or a combination of a polymeric film, a metallised foil, a woven fabric, a knitted fabric, a paper based material including kraft paper and kraft board.

Step a) may include extruding the adhesive between the flexible medium and an outer face of the first film that is opposite to the inner face of the first film having the solar active material, to form a layer of the adhesive therebetween .

Step b) may include passing the first film and flexible medium with adhesive therebetween through a second nip formed between a pair of rollers of which at least one of the rollers is operably movable to adjust the gap

therebetween to press the first film and the flexible medium together. In the instance when joining the first film and the flexible medium is a preliminary step before joining the first and second films, step b) may include one of the rollers contacting the inner face of the first film having the solar active material.

The rollers of the first and second nips may include a large diameter mother roller and smaller diameter running roller, and at least one of ^■ he rollers is moveable to adjust the gap therebetween , nd in turn adjust the pressure applied. For example, pressing the first and second films together may include adjusting the gap between the mother roller and the running roller of the first nip. Similarly, pressing together the first film and the flexible medium may include adjusting the gap between the mother roller and the running roller of the second nip. Adjusting the gap between the rollers may be carried out by operating an actuator that moves one of the rollers relative to the other.

The process may also include a cooling step in which the solar cell assembly contacts a cooling surface, for example, in the range of 10 to 25°C. Ideally, the cooling surface is provided by the mother roller and the solar cell assembly is subjected to the cooling step on passing through the first nip and is conveyed along a path that is in part defined by the outer circumference of a mother roller. The mother roller may be cooled using any suitable means and is ideally constructed with a water jacket which receives cooling water. Ideally, the water jacket extends about the circumference of the mother roller.

The first and second active solar materials on the first and second films can be preapplied using any suitable means or techniques, including physical vapour deposition sputtering, and printing techniques including 3D printing wired bar coating, inkjet printing, doctor blade coating, spray coating, screen printing, and so forth. Typically, the active solar materials include conductive electrodes which may, for example, be in the form of conducting inorganic or organic materials such as polymers and semiconductors having different gapbands that have different spectral absorption properties. Moreover, typically a photovoltaic solar cell having a p-type donor semiconductor and an n-type acceptor semiconductor will be assembled to form with a p-n junction in the solar cell in a conventional manner. Typical materials include

crystalline silicon doped with boron and phosphorous.

However, there is also a range of other materials and compositions that can be used, such as semiconducting layers made of materials including cadmium telluride (CdTe), copper indium diselenide (CIS), copper indium gallium diselenide (CIGS), amorphous silicon (a-Si) , perovskites, BTR (benzodithiophene terthiophene

rhodanine), and various other inorganic and organic compounds . When in use, photon are absorbed by the semiconductor materials, which in turn causes the disassociation of free electrons and holes within semiconductor materials, which in turn generates a current which can be collected by electrodes .

In an embodiment, the first solar active material may include a first sub-cell and the second solar active material may include a second sub-cell, and the solar cell assembly is in the form of a tandem solar cell.

The first solar active material may be a first portion of a photovoltaic cell, such as for example, an electrode. The second solar active material may be a second portion of a photovoltaic cell, including a second electrode and a semiconductor material having acceptor and donator portions for generating an electrical current. It is not essential that both the first solar active material and the second solar active material include both a donor semiconductor and an acceptor semiconductor. Either one or both of the first and second films may also a polymeric sheet, such as a PET (Polyethylene

terephthalate ) , polyvinyl, polyesters and so forth.

BRIEF DESCRIPTION OF THE DRAWINGS

A preferred embodiment of the present invention will now be described with reference to the accompanying drawings, of which: Figure 1A is a schematic illustration of a process that joins together first and second films having first and second solar active materials on inner faces thereof are joined together to the form a flexible web having a solar cell assembly;

Figure IB is a schematic illustration of a process that joins together the web having the solar cell assembled according to Figure 1A, and a medium such as, but by no means limited to fabric, paper or a polymeric sheet;

Figure 2 is a schematic illustration of a process that joins together, in a first step, a first film having a first solar active material to a medium that is free of solar active material, and in a second step, that joins a second film to the first film to form a web having a solar cell assembly; Figure 3 is a schematic illustration of a converting step for forming electrical bridges between the first and second active materials;

Figures 4 and 5 are schematic cross-sectional views of the first and second films including first and second solar active materials respectively, figures 4 and 5 being an enlargement of the views shown in figure 2 ; and

Figure 6 is a schematic cross-sectional view of a web product including a solar cell assembly.

DETAILED DESCRIPTION

Figure 1A is a schematic illustration of a process 20 for assembling a solar cell. The process 20 includes

conveying, from a roll, a continuous length of first film 10 having a first solar cell active material pre-applied on an inner face of the first film 10 towards a nip 11 formed between two rollers 12, 13.

The process 20 also includes conveying, from a roll, a continuous length of the second film 14 having a second solar cell active material pre-applied on an inner face of the second film 14 toward the nip 11, and extruding an adhesive 15 from an extrusion head 16 at an elevated temperature range onto the inner face of at least one of the first film 10 and the second film 14. Once the adhesive 15 has been applied, the process includes pressing the first and second films 10, 14 together with the inner faces of the first and second films 10, 14 facing toward each other by passing the films through the nip 11 formed between the two rollers 12, 13 and pressing the first and second films together forms flexible web including a solar cell assembly. The rollers 12, 13 forming the nip 11 for pressing the first and second films 10, 14 may be any suitable rollers 12, 13. In the case of the embodiment shown in figure 1A, the rollers are in the form of a large diameter mother roller 12 that is water cooled, suitably having a water cooling jacket, and a smaller diameter running roller 13 having an actuator 17 for moving the running roller 13. The actuator 17 is ideally operable for adjusting the spacing between the outer surfaces of the running roller 13 to the mother roller 12. In other words, pressing the first and second films 10, 14 together may include controlling the pressure applied to the first and second films 10, 14 passing through the nip 11 formed by the rollers .

The mother roller 12 may be connected to any suitable source of cooling water, including a closed loop cooling water circuit 18. In addition, as can be seen the web 19 formed follows a path about at least part of the

circumference of the mother roller 12 in order to achieve a degree of cooling whilst in contact with the mother roller 12.

The extrusion head 16 may have any suitable construction for extruding a continuous or discontinuous layer of adhesive 15. Suitably, the extrusion head 16 operates at a temperature in the range of 200 to 300°C, and is capable of extruding polymeric material such as, but by no means limited to thermoplastic polymers, such as polypropylene and polyethylene. The extruded materials could also consist of a series of layers of different polymeric materials .

The temperature of the web 19 including the solar cell assembly, and the adhesive 15 between the inner faces o the first and second films 14 can be controlled, at lea in part, by controlling the temperature of the cooling water fed to the mother roller 12.

The adhesive 15 used for bonding together the inner faces of the first and second films 10, 14 and, in turn, the first and second solar active materials, may be any suitable adhesive 15 including a conductive adhesive and non-conductive adhesive. When the adhesive 15 is a non- conductive adhesive, in an optional embodiment the proces 20 also includes a step of forming electrical bridges at station 40 that interconnect the first solar active material and the second solar active material. Forming the electrical bridges may include pinching the web 19 so as to displace the adhesive 15 in selected locations between the first solar active material and the second solar active material to allow electrical contact

therebetween .

In one embodiment, the step of forming the electrical bridges may be carried out during die cutting or other converting steps . Figure IB is a schematic illustration of a step of the process in which a web 19 containing the solar cell assembly is joined to a flexible medium 21 not having solar active material. The medium 21 may, for example, be any suitable medium based on the intended application and ideally can be stored in a rolled formation. Examples of such materials could include polymeric films, woven fabric materials, non-woven fabric materials, paper and board materials, or any suitable combination of these materials.

The process includes conveying the medium 21 toward a second nip 22 formed between the two rollers 32, 33, applying an adhesive 35 to either the web 19 or the medium 21, and then passing the web 19 and medium 21 through the nip 22 formed between a second mother roller 32 and a second running roller 33. The second running roller 33 may be movable by an actuator 37, as described above, with reference to the first running roller so as to enable the spacing between the mother roller 34 and running roller 33 to be adjusted, and in turn, control the pressure applied to the medium 21 and the web passing through the nip 22.

The product 38 passing through the nip 22 extends about mother roller 32 which is water cooled, via cooling circuit 39. The product 38 is then wound into a roll for storage before further processing.

Figure 2 is a schematic illustration of the process 20 in which a flexible medium 21 is joined to an outside face o a first film 10 in a preliminary step. The process 20 includes a length of the flexible medium 21 being unwound from a rolled configuration and being conveyed toward a first nip 11 formed between a first mother roller 12 and first running roller 13. The process 20 also includes a length of the first film 10 being unwound from a rolled configuration and being conveyed toward the first nip 11. A first adhesive 15 is applied in a continuous or

discontinuous layer to an inner face of the first film.

The first adhesive 15 may be any suitable adhesive, including but by no means limited to, polyethylene, polypropylene or nylon, and may be applied using suitable means, including an extrusion head 16. The first film 10 and the flexible medium 21 are pressed together by passing through the first nip 11 and bonded together to form a pre-product that passes through the first nip circuit 18.

As can be seen, the pre-product 34 is conveyed along a path that extends about at least part of the circumference of the first mother roller 21. Optionally, the temperature of the first mother roller 21 can be controlled, for example, by means of cooling water circuit 18.

The temperature of the first adhesive 15 may, for example, when extruded from the extrusion head 16 be in the range of 200 to 300°C, and cool to a temperature in the range of 70 to 150°C when applied to the flexible medium 21. The pre-product may be cooled to a temperature to a

temperature in the range of 10 to 40 °C when leaving the first mother roller 21.

The pre-product 34 is then conveyed toward a second nip 22 formed between a second mother 32 roller and a second running roller 33. A continuous length of a second film 14 is unwound from a rolled configuration and conveyed toward the second nip. A second adhesive 35 is applied to either one of the inner faces of the pre-product 34 which is the inner face of the first film 10, or the inner face of the second film 14 so as to form a continuous or discontinuous adhesive layer. The pre-product 34 and the second film 14 are then pressed together with the adhesive 35

therebetween by passing through the second nip 22 so as to bond the first solar active material to the second solar active material and form flexible web 38 containing a solar cell assembly.

The second running roller 33 may be movable, for example, by means of a controller that operates an actuator 37 connected to the second running roller 33 to adjust the spacing between the second running roller 33 and the second mother roller 32. Similarly, the second mother roller 32 may be temperature controlled and the web 38 extends along a path part way around the second mother roller 32 to facilitate heat transfer between the web product 38 and the mother roller 38, and thereafter be wound into a rolled configuration.

As described above in relation to the first mother rolle 33, the second mother roller 32 may, for example, be cooled by means of cooling water of a coding circuit 39, and the temperature ranges of the second mother roller 3 the adhesive 35 and the temperature at which the web 38 containing the solar cell assembly is wound into a web product may be the same or similar to the pre-product described above.

The process 20 may also include registering the first solar active material and the second solar active material as required. The step of registering may include

operating an accumulator device 41 comprising one or more accumulation rollers 42 which in part define the path about which the first film or the second film passes. The accumulator device 41 enables the path about which one of the first or second films 10, 14 is conveyed from the rolled configuration to the respective nip. In the case of figure 2, the accumulator is operable to retain more, or alternatively, release more of the second film relative 14 to the first film and thereby achieve the desired registration.

The first and second films may also have demarcation symbols to allow the relative positions of the first and second films 10, 14 to be monitored, for example, by means of the photosensor. An output of the photosensor can be used to control operation of the accumulator device 41. For example an output of the photosensor can be used to control the positon of one or more of the rollers 42.

Figure 3 is a schematic illustration of a converting step 43 which may, depending on the characteristics of the adhesive 35 may be optional. In the situation in which the adhesive is non-conductive such as polypropylene, nylon, polyester and so forth, the converting step may include forming electrical bridges between the first and second active solar materials. In one example, the electrical bridges are permanent and may, for example, be formed by pinching the web product so as to displace the adhesive in segments from between the first and second solar active materials.

Although figure 3 illustrates the converting step 43 as a separate step, it possible that the converting step be carried out directly in line with the second mother roller, without any intervening steps and prior to the web product being wound. Figures 4 and 5 are schematic cross-sections of the first and second films including a polymeric sheet such as a PET sheet 50, and a first solar active material 51 and a second solar active material 52. When the first and second solar active materials are assembled in accordance with the process described herein, a solar cell assembly is formed.

In one example, the first and second solar active

materials may be sub-cells, and the process described herein facilitates the assembly of a tandem solar cell.

In another example, the first solar active materials may be an electrode, and the second solar active material may be another electrode and a semiconductor having a p-n junction, and the process includes the two being assembled together .

Figure 6 is a schematic cross-sectional view of a flexible web product 38 having a solar cell assembly including: the first film 10 made of PET having the first solar active material 10a, the second film 14 made of PET having the second solar active material 14a, the adhesive layer 15 bonding the first and second solar active materials 10a and 14a, and the flexible medium 21. The electrical bridges are represented by the step formations allowing direct electrical contact between the first and second solar active materials 10a and 14a.

It will be understood to persons skilled in the art of the invention that many modifications may be made to the embodiments described herein without departing from the spirit and scope of the invention.

In the claims which follow and in the preceding

description of the invention, except where the context requires otherwise due to express language or necessary implication, the word "comprise" or variations such as "comprises" or "comprising" is used in an inclusive sense, i.e. to specify the presence of the stated features but not to preclude the presence or addition of further features in various embodiments of the invention.