ITVI20120132A1 - BACKSHEET FOR PHOTOVOLTAIC MODULES INCLUDING CELLS CONTACT REAR - Google Patents

Description

DESCRIPTION

"BACKSHEET FOR PHOTOVOLTAIC MODULES INCLUDING THE REAR"

TECHNICAL FIELD OF THE INVENTION

The present invention relates to the field of photovoltaic modules. In particular, the present invention relates to a new concept backsheet for a photovoltaic module and a process for producing said base or backsheet. Even more particularly, the present invention relates to a backcontactbacksheet for a photovoltaic module in which a plurality of rear-contacted solar cells are mounted.

STATE OF THE TECHNIQUE

Solar cells are used to convert sunlight into electricity by means of the photovoltaic effect. Solar cells therefore represent one of the most promising alternative energy sources to replace fossil fuels. The solar cells are formed from semiconductor materials and are assembled to form the so-called photovoltaic modules which, in turn, are grouped to form the photovoltaic systems typically installed on the roofs of homes or the like.

To form the photovoltaic modules, groups of solar cells, grouped in series through suitable electrical conductors called "ribbons", are typically encapsulated by means of an encapsulating material such as for example polyvinyl acetate with a high content of ethylene vinyl acetate, commonly called EVA. The encapsulating material enclosing the solar cells is then inserted between a surface layer and a base or back-sheet in order to complete the photovoltaic module. The surface layer, or main surface of the module, typically made of glass, covers the surface of the module exposed to the sun and allows sunlight to reach the cells. The back-sheet, on the other hand, performs a variety of tasks. It ensures protection for the encapsulating material and for the solar cells from environmental agents, while preventing oxidation of the electrical connections. In particular, the back-sheet prevents humidity, oxygen and other factors related to atmospheric conditions from damaging the encapsulating material, the cells and the electrical connections. The back sheet also provides electrical insulation for the cells and corresponding electrical circuits. Furthermore, the back-sheet must have high opacity for aesthetic purposes and high reflectivity in the part oriented towards the sun for functional purposes.

Traditional photovoltaic modules are made from a plurality of layers. The lower layer consists of the backsheet, on which a first layer of encapsulant comprising ÈVA is placed. The cells are then deposited on the first encapsulant layer comprising ÈVA. The cells are arranged on the encapsulant to form strings, where the cells are connected in series with each other by means of ribbons. Adjacent strings are then connected by means of two or more connections called "busbars". A second layer of encapsulant is then placed on the cells and, on top of this, a glass. The electrical connection in photovoltaic modules including traditional solar cells takes place both on the front and on the rear side of the cell. The electrical connection to the electrode placed on the front side of the cell, that is the side exposed to the light radiation, is traditionally made by means of a series of essentially parallel filiform contacts called "fingers", connected by means of two or more ribbons arranged transversely with respect to the direction longitudinal of the fingers. This way of contacting the front electrode, also called "H-patterning", creates shading problems on the surface exposed to light radiation due to the presence of the fingers and ribbons, which shield the light incident on the front surface of the cell. Traditional electrical contacts therefore lead to a reduction in the efficiency of solar cells and modules.

The cells are also quite spaced from each other as the ribbons must be allowed to find the space to be folded in such a way as to pass from the upper side of a cell to the lower side of the adjacent cell. Furthermore, the need to make a connection between a string of cells and the adjacent string entails the need to find the space for the passage of the busbars.

In order to overcome these problems, solar cells with back contact or back contact cells have been devised. This family includes the following types of solar cells: Interdigitated Back Contact (IBC) cells, Emitter Wrap Through (EWP) cells, Metallization Wrap Through (MWT) cells. The cells contacted at the rear are advantageous in that they allow the contact with both electrodes of the cell to be transferred to the rear side of the cell, that is, to the side not exposed to light radiation. This reduces the shading effect and, therefore, the reduction of the effective cell surface exposed to radiation, due to the presence of ohmic contacts on the external surface of the cell.

A further advantage deriving from the use of cells contacted posteriorly lies in the fact that the module assembly process can be highly automated while eliminating a phase that is that of the syringing of the cells. Furthermore, since it is not necessary to provide connections via ribbon and busbar, the thickness of the encapsulant can be reduced with advantages in terms of light transparency and costs.

A type of cell contacted at the rear that is particularly efficient and convenient to make is given by MWT cells. Figures 1 a and 1b show, respectively, the front surface (i.e. surface exposed to light radiation) and the rear surface of an MWT cell. Figure 2 instead shows a cross section of an MWT cell.

An MWT cell is made starting from a doped wafer so as to obtain a junction between a zone 662 with free charges of a given polarity and a zone 664 with free charges of the opposite polarity. For example, zone 662 can be doped with n-type impurities and zone 664 doped with p-type impurities. The plane of the seam is generally parallel to the front and back surfaces of the wafer.

As shown in Figures 1b and 2, the electrode corresponding to the zone 664 is contacted by means of the electrode 640 formed directly on the rear side of the cell. On the other hand, the electrode corresponding to the zone 662 is contacted by means of the contact 620, which comprises several portions. As shown in Figures 1a and 2, the portion 622 of the contact 620 with the electrode 662 is formed on the front side of the cell and comprises the metal semiconductor junction by which the charge present in the electrode 662 can be collected. This charge is then transferred on the rear side of the cell to the rear portion 624 of the contact 620. The charge transfer occurs through the portion 626 of the contact 620, formed inside a through hole made through the wafer thickness. In this way, the presence of ribbons on the front surface of the cell is avoided, with a consequent increase in efficiency compared to the traditional architecture of a solar cell.

Figure 1b shows that the cell 600 shown in the figure comprises, on the rear side of the cell 600, 15 contacts 640 to the electrode of a given polarity and 16 contacts 624 to the electrode of the opposite polarity. Therefore in total there are 31 ohmic contacts on the rear surface of the cell 600.

The cells contacted later pose new technological problems regarding the design and structure of the modules intended to accommodate them. For example, the backsheet must be designed to support a connection circuit on which the connections to both electrodes (base and emitter) of the cell are carried. One of the solutions developed in order to tackle this problem is the so-called backcontact-backsheet, an evolution of the traditional backsheet in which the connection circuit is made directly on the surface of the backsheet facing the cell. The structure of the backcontactbacksheet will be described more fully in the following Figure 3 shows the structure of a photovoltaic module comprising solar cells contacted at the rear. The rear-contacted solar cell 600 is placed between a layer of upper encapsulating material 450 and a layer of lower encapsulating material 400. The cell 600 and layers 400 and 450 of encapsulating material are then enclosed between a surface layer 800 typically made of glass or in a transparent and anti-reflective material and the back-sheet 200, which can be a backcontact-backsheet. Figure 3 shows the tracks 220 of conductive material constituting the connection circuit to the electrodes of the solar cells. If the backsheet 200 is a backcontact-backshhet, the link circuit is formed directly on the surface of the underlying substrate and firmly attached to it. The connection circuit is used to ensure electrical contact with both electrodes, ie with the base and the emitter, of the solar cell 600. In particular, the conductive material tracks have pads 222, which mark the points of the connection circuit to be put in electrical connection with a contact to one of the electrodes formed on the surface of the cell 600.

The assembly of a photovoltaic module of the type illustrated in Figure 3 typically takes place according to the procedure described below.

The lower encapsulating material layer 400 to be placed between the cell 600 and the backsheet or backcontact-backsheet 200 is perforated so that the holes made in the lower encapsulating material layer 400 correspond to the areas in which the pads 222 are arranged for contact with the electrodes, once the module has been completed. The perforated encapsulating material layer 400 is then placed on top of the backsheet or backcontact-backsheet 200 so that the holes in the lower encapsulating material layer 400 correspond to or are aligned with the pads 222, so as to leave the pads 222 exposed towards the 'external.

A lump or drop of electrically conductive material is then deposited on the pads 222 of the conductive tracks 220 of the connection circuit formed on the surface of the backsheet or backcontact-backsheet 200. The surface of the pads 222 is left exposed by the holes in the layer of lower encapsulating material 400. The conductive material deposited on the pads 222 can for example comprise a conductive paste of the type known as "Electro Conductive Adhesive" (ECA).

Subsequently, the cells 600 to be incorporated into the module are placed on the lower encapsulating material layer 400 so that each element of contact with the electrodes formed on the rear surface of the cell comes into contact with a lump of conductive paste applied on one of the pads 222 and exposed to contact with the cells 600 through one of the holes made in the lower encapsulating material layer 400. The upper encapsulating material layer 450 is then placed on the upper surface of the cell 600, opposite the rear surface in contact with the conductive paste applied on the pads 222. Finally, a layer of transparent and anti-reflective material 800 is placed over the layer of upper encapsulating material 450.

Once the structure has been prepared as just described, it is turned upside down and then laminated under vacuum at a temperature between 145 ° and 165 ° for a time ranging from 8 to 18 minutes.

Figure 4a shows the structure of the module before the lamination process. The components of the module, stacked as described above, are individually distinguishable. In particular, figure 4a shows a stack comprising, starting from the bottom and going upwards of the figure, the backsheet or backcontact-backsheet 200 with the conductive pads 222 on which the conductive paste 300 has been affixed, the layer of lower encapsulating material 400, the cells 600, the upper encapsulating material layer 450 and the surface layer 800.

Figure 4b schematically shows the structure of the module after the lamination process. In the first stage of lamination, the structure is placed in a vacuum chamber from which the air is evacuated by means of pumps. A pressure is then applied to the structure to compact the different layers of which the module structure is composed, while maintaining the vacuum in the area where the module is located. The entire cycle preferably has a total duration of less than 18 minutes. The cycle preferably takes place at a temperature ranging from 140 ° to 165 °.

The lamination produces the hardening of the conductive paste 300 through its polymerization, thus causing the fixing of the cells 600 to the back-sheet 200. Furthermore, the lamination process also has the task of melting and subsequently polymerizing the layers of material. upper encapsulant 450 and lower 400. In this way, the encapsulating material of the lower layer 400, by melting, fills the voids between the conductive paste 300, the backsheet or backcontact-backsheet 200 and the back surface of the cells 600. Furthermore, by polymerization , the upper encapsulating material layer 450 also exerts an adhesive action between the surface layer 800 and the outer surface of the cells 600 in contact with the upper encapsulating material layer 450. Similarly, the lower encapsulating material layer 400 exerts after polymerization also an adhesive action between the rear surface of the cells 600 and the back-sheet 200.

The previous description highlights the technical and engineering difficulties that the production of a photovoltaic module entails.

First of all, drilling a plurality of holes in a sheet of encapsulating material such as ÈVA is not a trivial task, especially if the holes must have predetermined positions and the tolerance on the positioning error must be reduced to about 0.1 mm on an overall size of 1700 mm x 1000 mm. The tolerance is so low since each hole in the lower encapsulating material layer 400 must correspond to one of the contact pads 222 of the connection circuit. Therefore, the pattern of the holes in the lower encapsulating material layer 400 must exactly match the pattern according to which the pads 222 were made.

It must then be considered that the sheet of encapsulating material will have the dimensions of the module, i.e. typically 1.7 m x 1 m. These considerable dimensions make the operation of opening the holes even more difficult.

Furthermore, the encapsulating layer typically has no mechanical consistency and has high thermal expansion / shrinkage coefficients so its dimensional stability is limited. For example, when subjected to a tensile stress, a sheet or lamina of encapsulating material tends to extend viscoelastic. This characteristic of the encapsulating material makes the drilling operation even more difficult.

The number of holes to be opened is then very high. As previously described with reference to Figure 1b, 16 contacts at one electrode and 15 contacts at the other electrode are generally formed on the rear surface of an MWT cell. So 31 contacts in total. A photovoltaic module typically contains 60 or 72 cells. Therefore the number of holes to be made on the layer of encapsulating material will be equal to 1860 and 2232 in the case, respectively, of a module with 60 and 72 cells. The operation of opening the holes is therefore quite long and laborious, thus contributing to the increase in production costs. An extremely delicate operation in the production of a photovoltaic module is then the alignment between the lower layer of encapsulating material 400 with holes and the underlying back-sheet or backcontact-backsheet 200, on whose conductive pads 222 the conductive paste must be applied. Each hole in the lower encapsulating material layer 400 must in fact correspond exactly to the respective conductive pad 222. The margin of error in the alignment between the lower encapsulating material layer 400 and the back-sheet or backcontact-backsheet 200 is minimal, since one phase shift between the holes in the layer of encapsulating material and the conductive pads 222 involves the covering of the conductive pad 222 by the layer of encapsulating material 400 and, therefore, the lack of contact between one of the electrodes of the cell 600 and the backsheet or backcontactbacksheet 200. Even worse, a phase shift between the holes in the encapsulating layer 400 and the conductive pads 222 could cause the conductive paste to shed from the conductive pads 222 to unwanted areas of the back-sheet surface 200 exposed to the cells during subsequent steps. assembly of the photovoltaic module.

While being able to exactly align the holes of the lower encapsulating material layer 400 with the conductive pads 222 on the backsheet or backcontact-backsheet 200, a fundamental problem arises during the subsequent stages of module assembly. In fact, the position of the lower encapsulating material layer 400 with respect to the backsheet or backcontact-backsheet 200 must remain unchanged in the subsequent stages of the assembly process which include: deposition of the cells 600, deposition of the upper encapsulating material layer 450, deposition of the layer surface 800 and, finally, lamination.

It may happen that the structure to be assembled must be transported from one point to another of the production line when passing from one of the assembly steps mentioned above to the next. The lower encapsulating material layer 400 may further shift relative to the backsheet 200 when the upper encapsulating material layer 450 or the surface layer 800 are added to the structure as a result of the stresses received by the structure during the deposition process. Furthermore, it should be noted that during lamination the layer of encapsulating material 400 can deform by expanding or contracting in response to the increase in temperature. Therefore, keeping the position of the lower encapsulating material layer 400 fixed with respect to the backsheet or backcontact-backsheet 200 is a non-trivial task that a manufacturer of photovoltaic modules cannot avoid by resorting to the means made available by the known art.

In view of the aforementioned problems and of the disadvantages relating to the traditional assembly procedure of photovoltaic modules, an object of the present invention is to provide a backcontact-backsheet for photovoltaic modules and a method for producing the same which allow to overcome said problems.

In particular, one of the objects of the present invention is to provide a backcontact-backsheet for photovoltaic modules which allows a practical, economical and precise assembly of a photovoltaic module.

A further object of the present invention is to provide a backcontact-backsheet and a method for making such a backcontact-backsheet thanks to which an excellent degree of stability of the lower encapsulating material layer can be obtained during the various assembly phases of the photovoltaic module, so such that the layer of encapsulating material cannot move during the assembly of the module.

A further object of the present invention is to provide a backcontact-backsheet and a method for making such a backcontact-backsheet thanks to which it is possible to obtain greater precision in the final and intermediate structure of the module, relative to the holes, thus allowing a high degree of process repeatability and minimizing the waste of resources due to the production of defective products.

A further object of the present invention is to provide a backcontact-backsheet and a method for making such a backcontact-backsheet thanks to which the risks of unwanted contamination and spreading of the adhesive paste can be avoided during the assembly process of the photovoltaic module.

A further object of the present invention is to provide a backcontact-backsheet and a method for making such a backcontact-backsheet thanks to which the awkward and complex phases of drilling the lower encapsulating material layer and its alignment with the backcontact-backsheet can be avoided during the mounting and assembly procedures of the photovoltaic module.

The critical steps of drilling the lower encapsulating material layer and aligning the encapsulating material layer with the backcontact-backsheet are normally the responsibility of the PV module manufacturer. Therefore, a further object of the present invention is to provide a backcontact-backsheet capable of relieving a manufacturer of solar modules from the tasks of drilling and aligning the layer of encapsulating material, thus simplifying and economizing the assembly and / or production process of the solar modules.

BRIEF DESCRIPTION OF THE INVENTION

According to the present invention, there is provided a backcontactbacksheet for photovoltaic modules and a method for producing such a backcontact-backsheet based on the new and inventive concept that the assembly process of a photovoltaic module can be simplified, speeded up and made more precise if the material layer lower encapsulant is supplied together with the backcontac-backsheet forming an integral part of it.

On the basis of these considerations, the backcontactbacksheet for photovoltaic modules according to main claim 1 is proposed.

Preferred embodiments of the present invention are provided by the dependent claims and the following description.

The present invention also provides a method for producing backcontact-backsheet for a photovoltaic module as defined in claim 7 and in the following description.

BRIEF DESCRIPTION OF THE FIGURES

Further characteristics and advantages of the present invention will become clearer from the following description of the embodiments of the device according to the present invention represented in the drawing tables. In the drawing tables, identical and / or similar and / or corresponding parts are identified by the same reference numbers or letters. in particular, in the figures:

Figure 1a shows a top view of the external or front surface of a solar cell of the MWT type which can be defined as the sun side;

Figure 1b shows a top view of the inner or rear surface of a solar cell of the MWT type defined as the shadow side;

Figure 2 shows a cross section of a solar cell of the MWT type;

Figure 3 shows an exploded view of a portion of a photovoltaic module;

Figure 4a shows a cross section of a photovoltaic module prior to the lamination process;

Figure 4b shows a cross section of a photovoltaic module following the lamination process; Figure 5 shows a cross section of a conventional backcontactbacksheet;

Figure 6 shows a cross section of a backcontactbacksheet according to an embodiment of the present invention;

Figure 7a shows an intermediate step of the realization of a backcontact-backsheet according to an embodiment of the present invention;

Figure 7b shows an intermediate step of the realization of a backcontact-backsheet according to a further embodiment of the present invention;

Figure 8 shows a cross section of a system composed of a solar cell and a backcontact-backsheet according to an embodiment of the present invention.

DETAILED DESCRIPTION

In the following, the present invention will be described with reference to particular embodiments as shown in the attached figures. However, the present invention is not limited to the particular embodiments described in the following detailed description and shown in the figures but, rather, the described embodiments simply show several aspects of the present invention whose scope is defined by the claims.

Further modifications and variations of the present invention will be clear to the skilled person. Accordingly, the present description is to be considered as including all modifications and / or variations of the present invention, the purpose of which is defined by the claims.

Figure 5 schematically shows a backcontactbacksheet 200 for a photovoltaic module commonly used in the state of the art. The air side of the photovoltaic module is the one placed at the bottom, under the backcontact-backsheet 200 shown in figure 5.

The backcontact-backsheet 200 comprises an insulating complex or substrate 210 exposed to the air side of the photovoltaic module.

The insulating substrate 210 comprises a first insulating layer 212, an intermediate layer 214 and a second insulating layer 216.

The first insulating layer 212 has a surface exposed towards the air-side of the photovoltaic module and is used as a barrier against humidity, UV rays, oxygen and external agents that could penetrate the module and damage some of the component parts or cause the adhesive to degrade. polyurethane or polyester nature, yellowing it.

The internal surface of the first insulating layer 212 opposite the surface exposed to the air side is then in contact with an intermediate layer 214, which acts as a barrier against humidity and water vapor. The intermediate layer is typically made of aluminum, preferably with a thickness of between 8 and 25 µm.

The internal surface of the intermediate layer 214, opposite the surface in contact with the first insulating layer 212, is then in contact with the second insulating layer 216, which acts as an electrical insulator and as a further barrier.

A layer of conductive material 220 is then applied to the inner surface of the second insulating layer 216 opposite the intermediate layer 214. This layer of conductive material 220 applied to the surface of the second rear insulating layer 216 will subsequently be treated so as to form a pattern generally comprising elongated elements such as tracks, tracks, paths, etc. This pattern forms the connection circuit with the electrodes of the solar cells. Not being formed continuously on the inner surface of the second insulating layer 216, the conductive layer 220 generally leaves exposed some portions of the inner surface of the second rear insulating layer 216 on which it is applied.

The connection circuit obtained in the layer of conductive material 220 can be formed by means of one of the techniques commonly used for the production of printed circuits. For example, the connection circuit can be formed in the conductive layer 220 by means of an optical lithographic technique, in which a photoresist layer is uniformly applied to the surface of the conductive layer 220, exposed according to the pattern to be reproduced and then developed. The surface comprising the developed photoresist is then subjected to a chemical etching which produces the desired pattern. Finally, the residual photoresist is removed. Alternatively, the connection circuit can be formed on the layer of conductive material by means of an ablation process, to be obtained by mechanical means such as a cutter or by evaporation using for example a laser.

The conductive layer 220 then comprises pads 222 formed in predetermined positions of the pattern of which the conductive circuit in the conductive layer 220 is composed. The pads 222 will be placed in electrical contact with the ohmic contacts formed on the surface of the electrodes of the solar cells through a lump of conductive material. The pads 222 therefore ensure electrical contact with the solar cells mounted in the photovoltaic module and are formed in positions corresponding to the positions of the ohmic contacts 624 and 640 formed on the rear surface of the solar cell 600 and shown in Figures 1b and 2.

Again with reference to Figure 5, the backcontactbacksheet 200 then comprises a layer of dielectric material 240 deposited on the internal side of the backcontactbacksheet 200, ie on the side opposite the air side and facing the cells. Such a layer of dielectric material 240 is generally formed, for example by means of a screen printing process, in such a way that the dielectric material completely covers the portion of the surface of the second rear insulating layer 216 left exposed by the conductive layer 220 applied above it. The dielectric material thus has the function of electrically insulating two adjacent but disconnected traces or elements of the pattern formed by the conductive layer 220. Furthermore, the layer of dielectric material 220 has the function of neutralizing any surface currents that could flow on the surface of the substrate 210 on which the conductive material layer 220 and a portion of the dielectric material layer 240 are attached.

The layer of dielectric material 240 is then deposited so as to leave partially exposed the layer of conductive material 220. More specifically, the layer of dielectric material 240 has openings 242 located in correspondence with the pads 222 of the conductive layer 220 shown in figures from 3 to 5 and used to contact the electrodes of the photovoltaic cells. Thus the dielectric layer 240 leaves the conductive pads 222 exposed towards the internal side of the backcontact-backsheet 200, that is towards the side facing the cells.

Finally, the portions of the conductive layer 220 left exposed by the layer of dielectric material 240 are covered by a protective layer 260 so as to prevent the exposed surface of the layer of conductive material 220 from oxidizing, corroding, scratching or damaging in general. The protective layer 260 may comprise an organic material, which is generally deposited by screen printing. Alternatively, the exposed portions of the conductive layer 220 can be protected by a metallic layer applied from the origin to the exposed surface. For example, if the layer of conductive material 220 comprises copper, it can be protected by a thin layer of nickel deposited on the surface of the layer of conductive material 220 comprising copper. If layer 220 were aluminum, it could be coated with copper and then nickel or tin. The choice of aluminum would be competitive with copper for a reason of lower costs with the same electrical resistivity.

The back-sheet 200 shown in Figure 5 has the drawbacks described above, such that the subsequent assembly of the photovoltaic module is slow, expensive and not very precise. This is largely due to the fact that a layer of encapsulating material placed between the cells and the backcontact-backsheet must first be perforated and then kept perfectly aligned with the conductive pads 222 of the backcontact-backsheet during all stages of the assembly.

In order to overcome the drawbacks associated with backcontactbacksheets known in the state of the art, the backcontactbacksheet 200 for photovoltaic modules is proposed according to an embodiment of the present invention shown in Figure 6. The backcontact-backsheet 200 shown schematically in Figure 6 is a evolution of the traditional backcontact-backsheet 200 shown in Figure 5. Therefore, the parts identified with the same reference numbers have similar structure and functions in the two cases.

The backcontact-backsheet 200 according to the embodiment shown in figure 6 comprises: an insulating substrate 210 comprising a lower or rear or external surface exposed to the air-side of the photovoltaic module and an upper or internal surface opposite the surface exposed to the air-side and a layer of conductive material 220 coupled to the upper or inner surface of the insulating substrate 210. The backcontact-backsheet shown in Figure 6 further comprises a layer of dielectric material 240 attached to the upper or inner surface of the insulating layer 210 and to the layer of conductive material 220 so as to partially cover the connection circuit formed in the conductive layer 220. The layer of dielectric material 240 comprises a lower surface facing the insulating substrate 210 and an upper surface opposite the lower surface. The layer of dielectric material 240 has a plurality of through openings 242, each located in correspondence with one of the conductive pads 222 formed in the connection circuit for contacting the electrodes of the photovoltaic cells.

The backcontact-backsheet shown in Figure 6 further comprises a protective layer 260 applied at least to the exposed portions of the layer of conductive material 220. Finally, a layer of encapsulating material 280 is coupled to the upper surface of the backcontact-backsheet 200 facing the photovoltaic cells.

The layer of encapsulating material 280 is fixed to the upper surface of the layer of dielectric material 240 below so as to adhere integrally to the layer of dielectric material 240. Furthermore, the layer of encapsulating material 280 is formed so as to have a plurality of through holes 282 Each hole 282 of the layer of encapsulating material 280 corresponds to an opening 242 of the layer of dielectric material 240. Each hole 282 of the layer of encapsulating material 280 is therefore aligned with and communicating with the corresponding opening 242 of the layer of dielectric material 240 in so as to form a single opening 286 which leaves exposed predetermined portions of the layer of conductive material 220 covered by the protective layer 260. In particular, the conductive pads 222 shown in Figures 3 to 6 and covered by the protective layer 260 are left exposed through the openings 286 of the layer of encapsulant material and 280 and of the dielectric material layer 240. In this way a backcontact-backsheet is provided in which the lower encapsulating material layer 400 is included in the backcontact-backsheet and integrally fixed thereto. In this way, the manufacturer of photovoltaic modules no longer has to pose the problem of having to drill the lower encapsulating material layer before mounting, so that the holes on the encapsulant layer reproduce the same pattern as the pads on the connecting circuit of the layer. of conductive material. In addition, the solar module manufacturer can speed up, simplify and economize production while improving quality. In fact, thanks to the backcontact-backsheet shown in figure 6, all the risks associated with the displacement of the layer of encapsulating material with respect to the backcontact-backsheet are eliminated during all stages of the assembly.

According to an embodiment of the present invention, the insulating substrate 210 can comprise a first insulating layer 212, an intermediate layer 214 and a second insulating layer 216.

The first insulating layer 212 may comprise a polymer such as polyvinylfluoride (PVF), polyvinyldenfluoride (PVDF), polyethylene terephthalate (PET) or other polymers. The first insulating layer 212 may have a thickness of approximately 25-75 µm or greater. The intermediate layer 214 may comprise a non-transparent material to water vapor such as aluminum. The intermediate layer 214 can have a thickness ranging from 8 to 25 µm. The second insulating layer 216 may comprise a polymer such as polyethylene terephthalate (PET) or the like. The second insulating layer 216 may have a thickness of approximately 125-350 µm or greater.

According to a further embodiment of the present invention, the intermediate layer 214 is not present and the insulating substrate 210 comprises only a first insulating layer 212 and a second insulating layer 216 directly coupled to the first insulating layer 212.

According to an embodiment of the present invention, the conductive layer 220 can comprise a metal with high electrical conductivity such as copper, aluminum or the like. According to a further embodiment, the conductive layer 220 comprises an aluminum base on which a thin layer of copper is deposited.

According to an embodiment of the present invention, the conductive layer 220 can be formed from a pre-printed sheet in the form of a circuit which is then applied to the surface of the second insulating layer 216 facing the interior of the photovoltaic module. According to a further embodiment of the present invention, the conductive layer 220 can be applied homogeneously and continuously on the surface of the insulating substrate 210 so as not to have holes or openings. The connection circuit can then be formed on this continuous layer by means of one of the techniques described above with reference to Figure 5, i.e. traditional chemical etching, mechanical milling, laser ablation, etc. The conductive layer 220 can have a thickness of approximately 25 to 70 µm.

The protective layer 260 may comprise an organic material. Alternatively or in addition to the organic material, the protective layer 260 may comprise a thin layer of a metal such as nickel, tin, silver or a combination of metals deposited on the surface of the conductive material layer 220 facing the interior of the photovoltaic module. The protective layer can have a thickness of between 2 and 5 µm. The protective layer 260 can be formed on the layer of conductive material 220 prior to the application of the layer of conductive material 220 on the surface of the substrate 210 of the backsheet-backcontact 200.

According to alternative embodiments of the present invention, the dielectric material layer 240 comprises a resin selected from acrylic, polyester, copolyester, epoxy or epoxy phenolic resins. According to other embodiments of the present invention, the layer of dielectric material 240 comprises a resin selected from among the thermoplastic resins or among the thermosetting resins and in any case among the resins commonly used in electronics for similar applications.

According to an embodiment of the present invention, the dielectric material layer 240 has a thickness of between about 10 and about 20 µm.

According to some embodiments of the present invention, the encapsulating material layer 280 comprises materials such as polyvinyl acetate, polyolefins, thermopolyolefins, polyethylene monomers or polymers, silicones, ionomers, or EVA. According to an embodiment of the present invention, the encapsulating material layer 280 has a thickness of about 200 to about 600 µm.

The backcontact-backsheet 200 shown in figure 6 allows to speed up, simplify and make more precise the assembly operations of a photovoltaic module, thanks to the fact that the punching and alignment with the backcontact-backsheet of the layer of encapsulating material placed between the cells and the backcontact-backsheet are no longer required. In fact, the layer of encapsulating material which, upon completion of the module, will be found between the cells and the conductive layer of the backcontact-backsheet is provided as an integral part of the backcontact-backsheet 200 according to the embodiment of the invention shown in Figure 6. Therefore, during the assembly of the module, the photovoltaic cells can be placed directly above the backcontact-backsheet 200 shown in figure 6, without any need to interpose a sheet of encapsulating material between the cells and the surface of the backcontact-backsheet facing the cells, being the layer of encapsulating material 280 already included in the backcontactbacksheet. In this way, the layer of encapsulating material 280 supplied with the backcontact-backsheet 200 of figure 6 and integral with it replaces the sheet 400 of encapsulating material used during the traditional assembly of a photovoltaic panel and shown in figures 3, 4a and 4b.

Figures 7a and 7b show alternative methods for making a backcontact-backsheet according to two alternative embodiments of the present invention

The method according to the embodiment shown in Figure 7a provides that the layer of dielectric material 240 is deposited in a continuous and full-bottomed manner on the insulating substrate 210 and on the layer of conductive material 220 which forms a pattern constituting the connection circuit with the electrodes of the cells, as described above. Again as described in relation to Figures 5 and 6, the layer of conductive material 220 is covered by the layer of protective material 260. The layer of dielectric material 240 is thus deposited so as to uniformly cover the entire surface of the connection circuit. In particular, just after the deposition of the layer of dielectric material 240, the conductive pads 222 for the connection with the contacts on the cell are covered by the layer of dielectric material 240 deposited. The deposition of the layer of dielectric material 240 can take place for example by means of full web coating, gravure, offset, spray coating or other similar techniques known to the person skilled in the art.

The method according to the embodiment shown in Figure 7b, on the other hand, provides for the layer of dielectric material 240 to be deposited so as to form a plurality of through holes 242 in predetermined positions. More specifically, the holes 242 are formed in the dielectric material layer 240 so that it leaves exposed those portions of the connection circuit formed in the conductive material layer 220 corresponding to the pads 222, possibly covered by the protective layer 260. This type of deposition of the dielectric material layer 240 is similar to that described with regard to the traditional backcontactbacksheet shown in Figure 5. The deposition of the dielectric material layer 240 can take place for example by means of a screen printing process.

In both the case of the embodiment shown in Figure 7a and in that of the embodiment shown in Figure 7b, the encapsulating material layer 280 is then coupled or attached to the upper surface of the dielectric material layer 240 facing inward of the module. photovoltaic, ie towards the cells 600. It is preferable that the layer of encapsulating material 280 shown in Figures 7a and 7b and coupled to the layer of dielectric material 240 is initially a continuous and connected sheet, without openings. Figure 8 shows the final step of the process for producing a backcontact-backsheet according to the embodiments shown in Figures 7a and 7b.

Once the encapsulating material layer 280 has been attached to the dielectric material layer 240, the encapsulating material layer 280 is treated to drill holes therein. As shown in Figure 8, through holes 282 are opened in the layer of encapsulating material 280 in predetermined positions corresponding to as many predetermined positions on the connecting circuit formed in the layer of conductive material 220. More specifically, each hole 282 is made in the layer of encapsulating material 280 at a pad 222 on the connection circuit.

According to the embodiment shown in Figure 7a, once the layer of encapsulating material 280 has been perforated, the through holes 242 are drilled in the dielectric material 240 in positions corresponding to the positions of the holes 282 of the layer of encapsulating material 280. The layer of dielectric material 240 can be perforated by ablation obtained by a technique such as mechanical ablation by milling, laser ablation, laser contouring or similar techniques known to the person of the art. The layer of dielectric material 240 can also be perforated by non-passing punching.

In the case of the embodiment shown in Figure 7b, it is not necessary to drill further through holes in the dielectric material layer 240 after drilling the encapsulating layer 280, since the dielectric layer 240 has been deposited so as to present the openings 242, each of which it is in correspondence with a pad 222 of the connection circuit. Since the through holes 282 of the layer of encapsulating material 280 have also been made in correspondence with the pads 222, after the drilling process of the encapsulating layer 280 it happens that each hole 282 of the layer of encapsulating material 280 is in correspondence with a hole 242 of the dielectric material layer 240 preformed at the time of deposition of the dielectric layer 240.

Therefore, as shown in Figure 8, each through hole 282 of the layer of encapsulating material 280 corresponds to a through hole 242 of the layer of dielectric material 240. The holes 282 and 242, being aligned, thus form a single opening 286 which leaves exposed a portion of the layer of conductive material 220 first covered by the layers of dielectric material 240 and of encapsulating material 280. More particularly, the corresponding holes 282 and 242 are made so as to expose the conductive pads 222, possibly covered by the protective layer 260 and formed on the conductive layer 220 in order to contact the electrodes of the cells. The pads or contact points 222 on the backcontact-backsheet can thus be put into electrical contact through the holes 242 and 282 with the ohmic contacts 640 or 624 on the rear surface of the cell 600 through the through holes 286 through the layers 240 and 280. Such ohmic contacts 640 and 624 can for example be formed, respectively, on the positive electrode (contact p) and on the negative electrode (contact n) of the photovoltaic cell 600, as also shown in Figure 2.

According to a particular embodiment of the present invention, the layer of encapsulating material 280 is weakly fixed (0.3 N / cm <peel <1 N / cm, where the term "peel" means an adhesion force) to the layer of dielectric material 240 below. The encapsulating material layer 280 can be attached to the dielectric material layer 240 by coextrusion, corona activation or by means of a weak adhesive deposited on the dielectric such as a solvent-based or solventless two-component polyurethane. According to this embodiment, the final fixing between the layer of encapsulating material 280 and the layer of dielectric material takes place during the lamination process of the entire photovoltaic module. The lamination causes the melting and subsequent adhesion with polymerization of the layer of encapsulating material (280). The lamination can be for example that described above with reference to Figure 4b.

According to an embodiment, the adhesion specification value between the encapsulant and the dielectric is reached during the lamination of the panel by reactivating the resin of the encapsulant, according to a procedure well known to the person skilled in the field of photovoltaic modules.

According to a particular embodiment of the present invention, the layer of encapsulating material 280 can be perforated by means of a non-through punching and subsequent removal of the portion of the layer of encapsulating material 280 punched. The removal of the punched portion can take place for example by suction. According to this embodiment it is preferable that the layer of encapsulating material 280 is weakly fixed to the layer of dielectric material 240 below. The removal of the punched portion of the layer of encapsulating material 280 is obtained in this way rather easily since the adhesion of the layer of encapsulating material 280 to the layer of dielectric material 240 below is reduced, since the layer of encapsulating material 280 is fixed only weakly to the layer of dielectric material 240. Punching then offers the advantage of repeatability, since a mold comprising a matrix can be used in which a plurality of punches is arranged so as to reproduce the pattern according to which the holes to be drilled on the layer of encapsulating material 280 must be arranged. This matrix may for example comprise 31 punches arranged to each correspond to the position of one of the ohmic contacts 624 and 640 on the rear surface of a cell 600 shown in Figure 1b. The mold with the matrix can then be translated by a predetermined distance and direction in order to drill the holes on the entire surface of the layer of encapsulating material 280 fixed to the layer of dielectric material 240, in turn fixed to the backcontact-backheet 200.

According to further embodiments of the present invention, the layer of encapsulating material 280 can be perforated by laser ablation, laser contouring with subsequent removal of the removed portion, or by mechanical milling.

According to a further particular embodiment of the present invention, the encapsulating material layer 280 is firmly fixed to the underlying dielectric material layer 240 by means of an adhesive or coextrusion so as to achieve a relatively strong bond between the encapsulating layer 280 and the dielectric layer 240. According to this particular embodiment, the perforation of the layer of encapsulating material 280 is preferably performed by evaporation or milling, since the adhesion between the layers 240 and 280 is high.

At the end of the drilling process of the layer of encapsulating material 280 and, in the case of the embodiment of Figure 7a, of the layer of dielectric material 240, a plurality of holes 286 are obtained (see Figures 6 and 8) which connect the conductive pads 222 on the circuit for connecting the layer of conductive material 220 with the outside. These conductive pads 222 exposed on the surface of the conductive layer 220 and formed in positions corresponding to the ohmic contacts 640 and 624 on the rear surface of the cells 600, can then be electrically contacted with the ohmic contacts 640 and 624 on the cell 600 shown in Figure 8. . As previously described, the electrical contact between the pads 222 and the ohmic contacts 640 and 624 is achieved by depositing a lump of conductive paste on each of the pads 222 and placing the cell on the backcontact-backsheet 200 so that each contact point 640 and 624 is in contact with the conductive paste applied to the corresponding pad 222. The subsequent steps of assembling the solar module can then proceed as described above.

According to a further embodiment of the present invention, after having perforated the layer of encapsulating material 280 and, in the case of the embodiment of figure 7a, the layer of dielectric material 240 so as to obtain the plurality of holes 286 which expose the conductive pads 222 on the connecting circuit of the layer of conductive material 220, a layer of electrically conductive adhesive material is deposited on the pads 222 through the holes 286. Preferably, the conductive adhesive material is deposited on the pads 222 in the form of a thin layer. According to a particular embodiment, the layer of electrically conductive adhesive material is deposited on each pad 222 exposed to the outside through the corresponding hole 286. According to an alternative embodiment, the layer of electrically conductive adhesive material is deposited on some predetermined pads 222 exposed to the outside through the corresponding holes 286. The layer of conductive adhesive material has the function of avoiding oxidation of the exposed surface of the pads 222 of the layer of conductive material 220. According to a particular embodiment, the layer of electrically conductive adhesive material comprises a paste such as ECA.

Although the present invention has been described with reference to the embodiments described above, it is clear to the person skilled in the art that it is possible to carry out various modifications, variations and improvements of the present invention in light of the teaching described above and within the scope of the claims. attached without departing from the object and scope of the invention. In addition to this, those areas that are considered to be known by those skilled in the art have not been described in order to avoid unnecessarily overshadowing the described invention. Consequently, the invention is not limited to the embodiments described above, but is limited exclusively by the scope of protection of the attached claims.

Claims (17)

CLAIMS 1. Backcontact-backsheet for a photovoltaic module comprising rear-contacted solar cells, said backcontact-backsheet comprising: a substrate (210) having an external surface exposed towards the air-side of said photovoltaic module and an internal surface opposite to said external surface and exposed towards the inside of said photovoltaic module, a layer of electrical conductive material (220) formed as a connection circuit to the electrodes of said solar cells and firmly adhering to said internal surface of said substrate (210), a layer of dielectric material (240) having a lower surface facing towards said layer of electrical conductive material (220) and said substrate (210) and an upper surface opposite to said lower surface, said layer of dielectric material (240) being deposited on said inner surface of said substrate (210) and said layer of electrical conductive material (220), said layer of dielectric material (240) being able to selectively insulate said circuit formed by said layer of electrical conductive material (240), having said layer of dielectric material (240) a plurality of through holes (242), each of said through holes (242) being adapted to leave exposed a predetermined portion of said layer of electrical conductive material (220), a layer of encapsulating material (280) coupled to said upper surface of said layer of dielectric material (240) so as to be stably fixed to said layer of dielectric material (240), said layer of encapsulating material (280) being provided with a plurality of through holes (282), each of said holes (282) of said layer of encapsulating material (280) being made in correspondence with one of said holes (242) of said layer of dielectric material (240) so as to leave said portion of said layer of electrical conductive material (220) left exposed by said hole (242) of said layer of dielectric material (240). 2. Backcontact-backsheet for solar cells according to claim 1 wherein said substrate (210) comprises a first insulating layer (212) of a first polymeric material having an external surface facing the air-side of the photovoltaic module and an opposite internal surface to said outer surface and a second insulating layer (216) of a second polymeric material coupled to said inner surface of said first insulating layer (212). Backcontact-backsheet according to claim 1 wherein said substrate (210) comprises: a first insulating layer (212) of a first polymeric material having an external surface facing the air side of the photovoltaic module and an internal surface opposite to said external surface , an intermediate layer (214) of a vapor impermeable material coupled to said inner surface of said first insulating layer (212), said intermediate layer having a lower surface facing towards said first insulating layer (212) and an upper surface opposite to said surface inferior, a second insulating layer (216) of a second polymeric material coupled to said upper surface of said intermediate layer (214). Backcontact-backsheet according to one of claims 1 to 3 wherein said layer of encapsulating material (280) comprises polyethylene or Ethylene Vinyl Acetate (ÈVA) or silicones or ionomers or polyolefins or thermopolyolefins. 5. Backcontact-backsheet according to one of claims 1 to 4 wherein said layer of conductive material (220) comprises copper, or copper coated with nickel or copper coated with silver, or aluminum, or aluminum coated with copper, or aluminum coated with copper in turn coated with nickel or silver. 6. Backcontact-backsheet according to claims 1 to 5 wherein the portion of said layer of electrical conductive material (220) left exposed by each of said holes (242) of said layer of dielectric material (240) is covered by a layer of electrically conductive adhesive material acting as antioxidant of the exposed surface of said layer of electrically conductive material (220). 7. A method for producing a backcontactbacksheet for a photovoltaic module comprising rear-contacted solar cells, said method comprising: making a substrate (210) having an external surface exposed towards the air side of said photovoltaic module and an internal surface opposite to said external surface and exposed towards the inside of said photovoltaic module, application of a layer of electrical conductive material (220) adapted to be formed as a connection circuit to the electrodes of said solar cells, said application being carried out in such a way that said layer of conductive material (220) adheres firmly to said inner surface of said substrate (210), deposition of a layer of dielectric material (240) over said inner surface of said substrate (210) and said layer of electrical conductive material (220), said layer of dielectric material (240) having a lower surface facing said layer of conductive material electric (220) and said substrate (210) and an upper surface opposite to said lower surface, coupling of a layer of encapsulating material (280) on said upper surface of said layer of dielectric material (240), said coupling being carried out in such a way that said layer of encapsulating material (280) is stably fixed to said layer of dielectric material ( 240), opening a plurality of through holes (282) in said layer of encapsulating material (280), each of said holes (282) of said layer of encapsulating material (280) being made in a predetermined position corresponding to a predetermined position on said circuit connection formed in said layer of conductive material (220), said method being such that said opening of said through holes (282) in said layer of encapsulating material (280) is made after said coupling of said layer of encapsulating material (280) on said upper surface of said layer of dielectric material (240). Method according to claim 7 wherein said deposition of said layer of dielectric material (240) occurs in such a way that said layer of dielectric material (240) forms a plurality of through holes (242) at a predetermined portion of said layer of underlying electrical conductive material (220), and in which each of said through holes (282) of said layer of encapsulating material (280) is made in a position corresponding to one of said through holes (242) of said layer of dielectric material (240). Method according to claim 8 wherein said deposition of said layer of dielectric material (240) takes place by means of a screen printing process. Method according to claim 7 wherein said deposition of said layer of dielectric material (240) occurs in such a way as to deposit a continuous and solid-bottomed layer so as to completely cover said layer of underlying electrical conductive material (220). Method according to one of claims 7 to 10 further comprising opening a plurality of through holes (242) in said dielectric material layer (240), each of said through holes (242) of said dielectric material layer (240) being made in correspondence with one of said through holes (282) of said encapsulating material (280) in such a way as to leave exposed a predetermined portion of said layer of electrical conductive material (220), said opening of said plurality of said through holes (242) in said layer of dielectric material (240) being made after said opening of said plurality of through holes (282) in said layer of encapsulating material (280). Method according to claim 1 wherein said opening of said plurality of through holes (242) in said layer of dielectric material (240) is made by means of non-through punching, laser ablation or mechanical milling. Method according to one of claims 7 to 12 wherein said opening of said plurality of through holes (282) in said layer of encapsulating material (280) is made by means of non-through punching and subsequent removal of the punched portion of said layer encapsulating material (280). Method according to one of claims 7 to 12 wherein said opening of said plurality of through holes (282) in said layer of encapsulating material (280) is made by means of laser ablation, laser contouring or mechanical milling. Method according to one of claims 7 to 14 wherein the stable and permanent attachment of said layer of encapsulating material (280) to said layer of dielectric material (240) takes place during a lamination of said fully assembled photovoltaic module, said lamination causing the melting and polymerization of said layer of encapsulating material (280). 16. A method according to claim 15 wherein said lamination takes place in a vacuum cycle. Method according to one of claims 15 and 16 wherein said lamination takes place at temperatures between 140 ° C and 165 ° C.