Manufacturing process for a photovoltaic module by thermoforming a multilayer stack

Abstract

A method for manufacturing a photovoltaic module, the method comprising: i) placing a multilayer stack (1) between a mold (2) and a deformable membrane (3), the multilayer stack comprising, as components, a front-facing sheet comprising at least one polymer, a back-facing sheet comprising at least one polymer, at least one intermediate sheet and at least one photovoltaic cell sandwiched between the front-facing sheet and the back-facing sheet; ii) thermoforming the multilayer stack comprising: - applying fluid pressure to the face of the membrane opposite the multilayer stack, to shape the multilayer stack against the mold and the membrane; - heating the multilayer stack to a temperature suitable for bonding together the components of the multilayer stack so as to form the photovoltaic module.and - the cooling of the photovoltaic module and the suppression of fluid pressure. Figure for the abstract: Fig. 2,

Description

Title of the invention: Method for manufacturing a photovoltaic module by thermoforming a multilayer stack

[0001] The present invention relates to the manufacture of a photovoltaic module, in particular having a complex three-dimensional shape, in particular curved.

[0002] In order to best preserve the undeveloped natural space, it is necessary, in order to deploy a large number of photovoltaic modules, to integrate them into existing surfaces, for example buildings, infrastructure, consumer goods and in the field of mobility (vehicles).

[0003] However, these integrations require that the shape and mass of the photovoltaic modules be adapted to the support intended to hold them. Furthermore, for each photovoltaic module, it is necessary to guarantee performance and durability that comply with current regulations and to reduce the corresponding environmental footprint in order to meet the "net zero carbon" objective by 2035.

[0004] Known photovoltaic modules generally comprise several photovoltaic cells, capable of converting a luminous flux into an electric current, which are encapsulated in a laminate.

[0005] The laminate typically comprises: - a front face intended to be positioned facing the solar radiation incident on the photovoltaic cells and which is defined by a thermally tempered glass plate, with a thickness greater than 2 mm, generally between 2.8 mm and 6 mm, - a multilayer back face, generally containing polyvinyl fluoride, for example marketed under the name TEDLAR©, - photovoltaic cells coated by two adhesion films, called encapsulation films, generally made of ethylene-vinyl acetate, arranged between the front and rear faces.

[0006] The photovoltaic module may further comprise an aluminum frame, which supports the laminate and a junction box that allows for the integration of bypass diode or MOSFET protection or an electronic circuit. The junction box also allows for the electrical connection of several photovoltaic modules together.

[0007] The implementation of a thick tempered glass front panel is however not compatible with applications where the lightness of the photovoltaic module is required.

[0008] To lighten the laminate, it may be possible to thin the tempered glass sheet to a thickness of less than 2 mm, or to replace it with a polymer sheet, made by examples include PVDF, ETFE, ECTFE, or FEP, or a sheet of a composite material made of glass fibers immersed in an epoxy resin.

[0009] The laminate is obtained by a hot lamination process at a temperature of approximately 150 °C. However, the lamination process has several drawbacks. In particular, it requires that the heating and compression phase of the laminate and the subsequent cooling phase be carried out in separate devices. Furthermore, controlling the cooling rate after lamination is difficult, which complicates the implementation of this process with thermoplastic polymers that can crystallize, become whitish, diffuse light more, and exhibit lower transparency upon cooling. In addition, the laminate is generally heated using an oil circuit with a flash point of no more than 194 °C. The hot lamination process is therefore not suitable for shaping polymer materials for which forming temperatures above 180 °C are required.Finally, the hot lamination process only allows the manufacture of flat photovoltaic modules.

[0010] Furthermore, to produce modules with complex three-dimensional shapes, in relief, and in particular with one or more curves, it is known to implement processes such as bag molding, autoclave molding, resin transfer molding (RTM molding), and reaction injection molding (RIM molding). However, these processes require long implementation times, which makes them inefficient and industrially uncompetitive.

[0011] There is therefore a need for a new manufacturing process for a photovoltaic module which overcomes, at least in part, the disadvantages of the prior art.

[0012] The invention relates to a method for manufacturing a photovoltaic module, the method comprising: (i) the establishment of a multilayer stack between a mold and a deformable membrane, the multilayer stack comprising, as components, a front-face sheet comprising at least one polymer, a back-face sheet comprising at least one polymer, at least one intermediate sheet, and at least one photovoltaic cell sandwiched between the front-face sheet and the back-face sheet; (ii) thermoforming of the multilayer stack comprising - the application of fluid pressure to the face of the membrane opposite the multilayer stack, to shape the multilayer stack against the mold and the membrane, - heating the multilayer stack to a temperature suitable for bonding the components of the multilayer stack together to form the photovoltaic module, and - cooling of the photovoltaic module and suppression of fluid pressure.

[0013] The process according to the invention makes it possible to manufacture a photovoltaic module with a relief shape by applying uniform pressure to the multilayer stack. This avoids applying locally high stresses that could damage the photovoltaic cells. Furthermore, as will become apparent later, the process according to the invention allows the use of a wide variety of polymeric materials, for example PA, PC, PP, PET G, or PMMA, in particular those requiring forming temperatures above 170 °C. Finally, the implementation of the process makes it possible to reuse the mold and the membrane to manufacture several photovoltaic modules, and the manufacturing time of a photovoltaic module is faster than with the prior art bag molding, RIM molding, and RTM molding processes.

[0014] Devices comprising a mold and a membrane for carrying out the thermoforming of parts are described for example in WO 2009 / 125079 A2, WO 2012 / 131112 A2 and WO 2013 / 190020 A1.

[0015] Unless otherwise stated, the pressures expressed in this description and in the claims are absolute.

[0016] The membrane is particularly suitable for conforming to the shape of the mold face against which the multilayer stack is pressed.

[0017] Preferably, the mold temperature is below 50 °C, preferably below 30 °C, prior to the placement of the multilayer stack between the mold and the membrane.

[0018] Preferably, the method comprises evacuating, to a residual vacuum pressure of 1000 Pa or less, the internal space delimited by the mold and the membrane in which the multilayer stack is housed and, optionally, the space delimited by the face of the membrane on which the fluid pressure is applied. Evacuating the air prevents gas bubbles from becoming trapped between the components of the multilayer stack, which degrade the properties of the photovoltaic module by facilitating moisture penetration and / or acting as a delamination initiation zone between the components.

[0019] Preferably, the residual vacuum pressure is less than or equal to 1000 Pa, preferably less than or equal to 300 Pa, or even less than or equal to 100 Pa.

[0020] The heating of the multilayer stack can be initiated before, concurrently, or after the evacuation of the internal space.

[0021] Preferably, the residual vacuum pressure is reached before the temperature of the intermediate sheet reaches at least 90 °C, or even at least 80 °C. This allows the gas contained between the components of the multilayer stack to be evacuated from the internal space before the intermediate sheet melts under the effect of its temperature. The temperature of the intermediate sheet is determined for example from a measurement made using a calibration multilayer stack equipped with a thermocouple placed in contact with the intermediate sheet and which has been previously subjected to step ii) of thermoforming, or from the result of a thermal modeling of the thermoforming of the multilayer stack, for example by the finite element method.

[0022] Preferably, the residual vacuum pressure is reached while the fluid pressure applied to the membrane is less than or equal to 20 kPa, or even before the fluid pressure is applied to the membrane, in order to avoid the formation of gas bubbles trapped in the photovoltaic module and / or to reduce the risk of damage to the photovoltaic cell(s).

[0023] In particular, the vacuum time to lower the pressure in the internal space, from atmospheric pressure to residual vacuum pressure, can be less than 60 s, preferably less than 30 s.

[0024] Preferably, the process includes heating at least the mold to raise the temperature of the multilayer stack. The heat from the mold is then transferred to the multilayer stack, in particular by radiation and / or conduction.

[0025] Preferably, the mold is heated by electromagnetic induction, which allows the heating to be localized at the interface between the mold and the multilayer stack and ensures that the temperature of said interface is substantially uniform. The difference between the mold temperature and the temperature of the multilayer stack at said interface is preferably less than or equal to 5 °C, in absolute value.

[0026] Preferably, the mold heating includes a temperature rise step, from the mold temperature when the multilayer stacking space is set up to a holding temperature followed by a holding step at the holding temperature.

[0027] The temperature rise step can be carried out at a rate between 1.8 °C.s1 and 2.5 °Cs-*.

[0028] The holding temperature can be greater than or equal to 170 °C, or greater than or equal to 180 °C, or greater than or equal to 200 °C, or greater than or equal to 220 °C, or greater than or equal to 250 °C, or greater than or equal to 280 °C, or greater than or equal to 300 °C.

[0029] The duration of the holding step can be between 1 minute and 15 minutes, preferably between 8 minutes and 12 minutes, better between 3 minutes and 5 minutes.

[0030] Preferably, the fluid pressure is applied to the membrane after the heating of the multilayer stack has been initiated, so as to limit the risk damage to, or even rupture of, the photovoltaic cells. Preferably, the application of fluid pressure to the membrane is carried out after the mold temperature has reached the holding temperature.

[0031] The fluid pressure applied to the membrane is greater than or equal to atmospheric pressure. It is preferably greater than 100 kPa, preferably greater than 200 kPa. Preferably, it is greater than or equal to 300 kPa, or even greater than or equal to 400 kPa. Furthermore, it is preferably less than or equal to 2000 kPa, or even less than or equal to 700 kPa, or even less than or equal to 600 kPa.

[0032] Fluid pressure can be applied to the membrane for a period of between 1 minute and 15 minutes, in particular between 3 minutes and 5 minutes.

[0033] The fluid used to apply fluid pressure can be a liquid or a gas. Preferably, the fluid is a gas, for example air.

[0034] Preferably, the photovoltaic mold is cooled between the membrane and the mold, and preferably at the contact between the membrane and the mold. Advantageously, the heating of the multilayer stack, the application of fluid pressure, and the cooling of the module can thus be carried out within the same device. This makes the process according to the invention simpler to implement, as these steps are performed in a single cycle, and more efficient than a prior art lamination process that requires separate equipment to heat and cool the photovoltaic module.

[0035] Preferably, the cooling of the photovoltaic module is initiated before the fluid pressure is removed. This prevents the photovoltaic module from deforming during cooling, as it is not sufficiently constrained by the membrane.

[0036] Preferably, the method includes cooling the mold in order to cool the photovoltaic module by heat exchange between the mold and the photovoltaic module. The mold is cooled, for example, by circulating a heat transfer fluid, for example water, in contact with the mold. In particular, the cooling rate of the mold can be between 0.2 °Cs₁ and 2 °Cs₁, preferably between 0.4 °Cs₁ and 1.6 °Cs₂, for example 1.5 °Cs₂*.

[0037] Preferably, the fluid pressure is maintained on the membrane during the cooling of the photovoltaic module at least until the temperature of the intermediate sheet is less than or equal to 50 °C, or even less than or equal to 30 °C. In this way, sufficient mechanical properties are ensured in the photovoltaic module.

[0038] The breaking of the vacuum in the internal space, i.e. the return to atmospheric pressure from the residual vacuum pressure, can be carried out at a rate greater than 100 kPa·s. Preferably, it is carried out at a rate between 0.8 kPa·s and 1.7 kPa.s

[0039] Preferably, the fluid pressure is maintained on the membrane during the vacuum breaking.

[0040] The vacuum in the internal space can be broken during or after the cooling of the photovoltaic module.

[0041] The duration of step ii) of thermoforming can be between 1 minute and 15 minutes, preferably between 3 minutes and 5 minutes.

[0042] After cooling, the process may include extracting the photovoltaic module from the interior space.

[0043] The front face sheet is intended, after obtaining the photovoltaic module, to be placed between the solar radiation source and the photovoltaic cell.

[0044] Preferably, at least one of the sheets chosen from the front sheet and the back sheet is a multilayer.

[0045] Preferably, at least one of the sheets chosen from the front face sheet and the back face sheet comprises a thermoplastic polymer.

[0046] The thermoplastic polymer may have a melting temperature greater than or equal to 180 °C.

[0047] The thermoplastic polymer is for example chosen from polyolefin (TPO), epoxy resin, polypropylene (PP), polycarbonate (PC), polymethyl methacrylate acrylic (PMMA), glycolized polyester terephthalate (PET G), polyamide (PA), polyphenylene sulfide (PPS) and mixtures thereof.

[0048] For example: - the thermoplastic polymer is a polyolefin and the mold is maintained at a holding temperature of at least 120 °C, for example for less than 1 minute; or - the thermoplastic polymer is an epoxy resin and the mold is maintained at a holding temperature of at least 190 °C, for example, for approximately 3.5 minutes; or - the thermoplastic polymer is polypropylene and the mold is heated to a holding temperature of at least 225 °C, for example for approximately 2 minutes; or - the thermoplastic polymer is PA6 and the mold is heated to a holding temperature of at least 260 °C, for example for approximately 2.5 minutes; or - the thermoplastic polymer is PA11 or PA12 and the mold is heated to a holding temperature of at least 290 °C, for example for approximately 3 minutes; or

[0049] - the thermoplastic polymer is PPS and the mold is heated to the temperature of maintaining a temperature of at least 315 °C, for example for about 3.5 minutes.

[0050] Preferably, at least one of the sheets chosen from the front-facing sheet and the back-facing sheet, preferably the back-facing sheet, comprises a composite material having reinforcing fibers dispersed in a matrix in one polymer, preferably the thermoplastic polymer described above, the composite material being, for example, a woven or nonwoven fabric impregnated with the polymer. The reinforcing fibers may be carbon fibers, glass fibers, or natural textile fibers.

[0051] In one embodiment, the process involves manufacturing the back face sheet by thermoforming, as described in step ii), of a multilayer structure. This makes it possible, for example, to prepare a multilayer stack having a raised shape.

[0052] The heating conditions of the multilayer structure, the application of fluid pressure to the membrane, and the cooling of the back-face sheet may be identical or different from the thermoforming conditions of the multilayer stack. For example, the back-face sheet and the multilayer stack may be heated to different temperatures.

[0053] The multilayer structure may comprise several sheets, at least one of the sheets having been manufactured by thermoforming as described in step ii) of a multilayer element.

[0054] Furthermore, the photovoltaic cell preferably comprises a semiconductor, in particular silicon. Alternatively, it may be an organic, perovskite, or CIGS photovoltaic cell. For example, the photovoltaic cell may be of the PERC, TopCOn, HJT, Tandem, IBC, or MWT type.

[0055] The multilayer stack preferably comprises several photovoltaic cells, preferably arranged in a regular pattern along at least one direction in a plane parallel to or coinciding with the median plane of the multilayer stack.

[0056] Furthermore, the multilayer stack can have a planar or complex shape, including a curved shape. In particular, the multilayer stack can extend along one or more curved directions that differ from each other. It can have at least one surface with at least one raised relief and / or at least one recessed relief.

[0057] According to a preferred embodiment, the multilayer stack comprises, or is constituted by: - the multilayer backing sheet which has a ply comprising different or identical layers made of a woven or fabric of carbon fibers impregnated in a thermoplastic polymer, - several intermediate sheets, each made of a thermoplastic encapsulating film, - several photovoltaic cells electrically connected to each other, each in contact with the intermediate leaves and sandwiched between the leaves intermediaries, - the front face sheet which comprises, or even consists of, a thermoplastic polymer.

[0058] The mold may comprise at least one raised relief and / or at least one recessed relief against which the multilayer stack comes into contact during thermoforming.

[0059] The mold can be shaped so that the shape of the photovoltaic module has at least one curvature.

[0060] The mold is preferably metallic, for example made of steel.

[0061] The invention can now be better understood upon reading the detailed description that follows, the illustrative and non-limiting examples presented, and the accompanying drawing in which:

[0062] [Fig-1] is a schematic and cross-sectional view of a mold, of a membrane, a multilayer stack and the photovoltaic module obtained at different stages of an example of implementation of the process;

[0063] [Fig.2] represents, as a function of time t, expressed in minutes, the evolution of the temperature mold setpoint temperature Te expressed in °C (left scale), pressure in internal space P; expressed in mbar and fluid pressure Pf applied to the membrane, expressed in bar (right scale);

[0064] [Fig.3] represents the schematic evolution of the temperature Tp of the mul stack ticouche in different positions depending on the thickness of the multilayer stacking as a function of time t; and

[0065] [Fig.4] and [Fig.5] are photographs of examples of a back face sheet and of a part of a multilayer stack respectively prior to thermoforming.

[0066] Figure 1 schematically illustrates different stages of an example of implementation of the process according to the invention, and Figures 2 and 3 show the evolution of different operating parameters of the process.

[0067] The process includes thermoforming a multilayer stack 1 using a mold 2 and a membrane 3.

[0068] In step i), as illustrated in [Fig. 1 a), the multilayer stack is placed between the mold and the membrane. The mold temperature Tc and / or the membrane temperature are preferably below 50 °C, preferably at room temperature.

[0069] The thermoforming of the multilayer stack against the mold is then carried out in step ii).

[0070] The lateral edges 4 of the membrane are brought into contact with the mold, then the gas contained in the internal space 5 delimited by the inner face 6 of the membrane and the inner face 7 of the mold, each of which is opposite the mul- stack ticouche 1, is aspirated as illustrated in [Fig.l] b).

[0071] The aspiration of said gas can be carried out by means of a pump through orifices which open through the inner face of the mold.

[0072] The aspiration of the gas induces a vacuum ¢0 of the internal space 5. The vacuum can be carried out in two stages, as illustrated in [Fig.2]. The pressure in the internal space P; can first be reduced from atmospheric pressure to an intermediate pressure Pint, for example of 300 Pa (3 mbar), and then to a residual vacuum pressure Pvr of 100 Pa (1 mbar).

[0073] A setpoint temperature Te is then applied to heat the mold. The mold heating process includes a temperature rise phase, for example, along a linear ramp, followed by a holding phase, for example, at 170 °C as illustrated in [Fig. 2]. A higher or lower setpoint temperature can, of course, be applied depending on the melting temperature of the components. Furthermore, the setpoint temperature Te can be applied to the mold before the residual vacuum pressure is reached. The mold is preferably heated by electromagnetic induction.

[0074] The temperature of the multilayer stack Tp is higher at its faces in contact with the mold and the membrane than at the intermediate sheet(s). As can be seen in [Fig. 3], in the illustrated example, it evolves substantially linearly with time, like the mold setpoint temperature.

[0075] The fluid pressure Pf is applied progressively to the outer face 8 of the membrane opposite the multilayer stack, preferably as soon as the temperature of the intermediate sheet reaches 80 °C. In the illustrated example, it is applied once the setpoint temperature reaches the mold holding temperature and is constant, at approximately 350 kPa. Alternatively, an initial intermediate fluid pressure step can be applied before applying the maximum fluid pressure value, particularly to reduce the risk of rupture of the photovoltaic cell(s) during component heating.

[0076] The fluid pressure deforms the membrane, the inner face 6 of which comes into contact with the opposite face 9 of the multilayer stack. It thus deforms the multilayer stack which comes into contact against the recessed 10 and protruding 11 reliefs of the inner face 7 of the mold, as illustrated in [Fig. 1] c).

[0077] The setpoint temperature Te of the mold is maintained at the holding temperature for an appropriate duration, for example between 180 °C and 260 °C so that the sheets which form the multilayer stack are irreversibly bonded to obtain the photovoltaic module.

[0078] The heating of the mold is then stopped. As illustrated in [Fig. 2], The mold's setpoint temperature can be reduced linearly. The mold is cooled during a phase (3), for example, by circulating water. Fluid pressure is maintained on the membrane until the temperature of the intermediate sheet in the photovoltaic module is below 50 °C, or even below 30 °C. The photovoltaic module can then be extracted from between the membrane and the mold (phase 4). Example

[0079] An example of the realization of a multilayer stack and the implementation of the process according to the invention for manufacturing a photovoltaic module is detailed below.

[0080] The back face sheet was first prepared by thermoforming a multilayer structure between the mold and the membrane according to the steps described above.

[0081] The multilayer structure was formed by superimposing the following sheets one on top of the other.

[0082] A first sheet was obtained from a blank consisting of three plies, each made of a carbon fiber nonwoven fabric with a surface mass of 300 g / m² and pre-impregnated with polypropylene. The blank was shaped against the mold and the membrane by thermoforming according to the steps described above, with the application of a fluid pressure of 700 kPa on the membrane, heating the mold to a set temperature of 220 °C reached in 1 minute and 40 seconds, holding at the set temperature for 4 minutes, and cooling the mold for 1 minute and 30 seconds to a temperature of 30 °C. The fluid pressure was then removed, and the first shaped sheet was extracted from between the mold and the membrane.

[0083] A second sheet was obtained from a blank consisting of a ply made of carbon fiber fabric with a surface mass of 200 g / m² and two polypropylene felts, each 45 µm thick, on either side of the fabric. A transparent polyolefin film with a thickness between 25 µm and 60 µm (with a surface mass between 23 and 55 g / m²) was placed against the inner face of the mold to improve subsequent adhesion between the back sheet and the intermediate sheet. The blank was shaped against the mold and the membrane by thermoforming under the same operating conditions as the first sheet, except that the set temperature was 230 °C.

[0084] The back-face sheet, photographed in [Fig. 4], was then formed by stacking the first and second sheets one on top of the other. The resulting multilayer structure was positioned opposite the mold, and the second sheet opposite the membrane. The multilayer structure was shaped against the mold and the membrane by thermoforming under the same operating conditions as the second leaflet.

[0085] A multilayer stack was then prepared by stacking the following sheets in the following order: - front face sheet made of a polyethylene terephthalate-based film with a thickness of 0.28 mm, - two intermediate sheets, each 600 µm thick, made of a thermoplastic encapsulant having a Young's modulus of 18 MPa, - photovoltaic cells, each with a thickness between 0.14 mm and 0.18 mm and electrically connected to each other by interconnecting ribbons with a thickness between 0.1 mm and 0.3 mm, - an intermediate sheet with a thickness of 600 µm, made of a thermoplastic encapsulant having a Young's modulus of 18 MPa, and - the back face sheet described above.

[0086] The multilayer stack, photographed in [Fig.5], was placed between the mold and the membrane, with the front face sheet facing the inner face of the mold.

[0087] The multilayer stack was shaped against the mold and the membrane by thermoforming according to the steps described above. The multilayer stack was first placed under vacuum in the internal space at a residual vacuum pressure of less than 1 kPa for 3 minutes and 10 seconds. The mold was heated from approximately 30 °C to a set temperature of 170 °C for 1 minute and 17 seconds and then held at the set temperature for 5 minutes. A fluid pressure of 350 kPa was applied to the membrane 3 minutes and 10 seconds after the start of mold heating. The mold was cooled for 1 minute and 30 seconds. The fluid pressure was then released, and the resulting photovoltaic module was extracted from between the mold and the membrane.

[0088] As is apparent from the present description, the invention makes it possible to manufacture a conformable photovoltaic module having a complex three-dimensional shape. It also allows the use of thermoplastic polymers that cannot be produced by a prior art lamination process. A photovoltaic panel with a low surface mass, less than 5 kg / m², and / or an aesthetically pleasing appearance, for example due to specific colors chosen for the thermoplastic polymers or due to an aesthetic effect provided by the fibrous materials, can thus be obtained.

Claims

Claims

1. A method of manufacturing a photovoltaic module, the method comprising: i) placing a multilayer stack (1) between a mold (2) and a deformable membrane (3), the multilayer stack comprising, as components, a front face sheet comprising at least one polymer, a back face sheet comprising at least one polymer, at least one intermediate sheet and at least one photovoltaic cell sandwiched between the front face sheet and the back face sheet, ii) thermoforming the multilayer stack comprising - applying fluid pressure to the face of the membrane opposite the multilayer stack, to shape the multilayer stack against the mold and the membrane, - heating the multilayer stack to a temperature suitable for bonding together the components of the multilayer stack so as to form the photovoltaic module,and - cooling the photovoltaic module and removing fluid pressure.,

2. Method according to claim 1, the temperature of the mold being less than 50°C, preferably less than 30°C, prior to the placement of the multi-layer stack between the mold and the membrane.

3. Method according to any one of claims 1 and 2, comprising placing under vacuum, at a residual vacuum pressure less than or equal to 1000 Pa, the interior space delimited by the mold and the membrane and in which the multilayer stack is housed.

4. Method according to the preceding claim, the residual vacuum pressure being reached before the temperature of the intermediate sheet is at least 90°C, or even at least 80°C.

5. A method according to any one of claims 3 and 4, the residual vacuum pressure being reached while the fluid pressure applied to the membrane is less than or equal to 20 kPa, or even before the application of the fluid pressure to the membrane.

6. A method according to any preceding claim, wherein heating of the multi-layer stack is initiated prior to application of fluid pressure to the membrane.

7. Method according to any one of the preceding claims, comprising heating at least the mold, in particular by electromagnetic induction, in order to raise the temperature of the multi-layer stack.

8. A method according to any preceding claim, wherein the fluid pressure is applied to the membrane after heating of the multi-layer stack has been initiated.

9. Method according to the preceding claim, the heating of the mold comprising a step of raising the temperature, from the temperature of the mold when placing the multilayer stack in place up to a holding temperature followed by a step of maintaining at the holding temperature, the holding temperature preferably being greater than or equal to 170°C, or even greater than or equal to 180°C, or even greater than or equal to 200°C, or even greater than or equal to 220°C, or even greater than or equal to 250°C, or even greater than or equal to 280°C, or even greater than or equal to 300°C.

10. Method according to the preceding claim, the temperature raising step being carried out at a rate of between 1.8 °Cs 1 and 2.5 °C «1

11. V-.S. Method according to any one of the preceding claims, the photovoltaic module being cooled between the mold and the membrane.

12. A method according to any preceding claim, wherein cooling of the photovoltaic module is initiated before the fluid pressure is removed.

13. Method according to the preceding claim, the fluid pressure being maintained on the membrane during the cooling of the photovoltaic module at least until the temperature of the intermediate sheet is less than or equal to 50°C, or even less than or equal to 30°C.

14. A method according to any preceding claim, wherein at least one of the sheets selected from the front face sheet and the back face sheet is a multilayer.

15. A method according to any one of the preceding claims, at least one of the sheets selected from the front face sheet and the back face sheet comprising a thermoplastic polymer, for example selected from a polyolefin (TPO), an epoxy resin, polypropylene (PP), polycarbonate (PC), polymethyl methacrylate acrylic (PMMA), polyester terephthalate glycol (PET G), polyamide (PA), polyphenylene sulfide (PPS) and their mixtures.

16. A method according to any one of the preceding claims, at least one of the sheets selected from the front face sheet and the back face sheet, preferably the back face sheet, comprising a composite material comprising reinforcing fibers dispersed in a matrix of a polymer, preferably a thermoplastic polymer selected from a polyolefin (TPO), an epoxy resin, polypropylene (PP), polycarbonate (PC), polymethyl methacrylate acrylic (PMMA), polyester terephthalate glycol (PET G), polyamide (PA), polyphenylene sulfide (PPS) and mixtures thereof, the composite material being for example a woven or non-woven fabric impregnated with the polymer.

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