WO2019201417A1

WO2019201417A1 - Layer assembly for a photovoltaic module

Info

Publication number: WO2019201417A1
Application number: PCT/EP2018/059639
Authority: WO
Inventors: Jordi Escarre Palou; Hengyu LI
Original assignee: CSEM Centre Suisse d'Electronique et de Microtechnique SA - Recherche et Développement
Priority date: 2018-04-16
Filing date: 2018-04-16
Publication date: 2019-10-24

Abstract

Layer assembly (1) for a photovoltaic module (17) comprising: - a front sheet (3) arranged on a light incident side of said layer assembly (1); - an optical filter (7) comprising at least one layer containing niobium oxide or titanium oxide, - an encapsulation layer (5) disposed between said optical filter (7) and said front sheet (3) and in intimate contact with said optical filter (7); characterized in that:10 - said front sheet (3) has an oxygen permeability of at least 10 cm³/(m².24hr.atm) at 20°C, and - said encapsulation layer (5) comprises free radical scavengers.

Description

LAYER ASSEMBLY FOR A PHOTOVOLTAIC MODULE

Technical Field

[0001] The present invention relates to the technical field of photovoltaic modules.

More particularly, it relates to a layer assembly for a photovoltaic module, the layer assembly comprising an optical filter.

State of the art

[0002] The natural colour of photovoltaic (PV) modules, also referred to as photovoltaic devices, solar cells or solar panels, tends to be near black, often with a purple or indigo tint, with a clearly-defined pattern of the individual cells being visible. When such PV modules are mounted on buildings they can be unsightly, and it is often unacceptable to use them directly as building cladding for this reason.

[0003] In order to overcome this problem, coloured PV devices have been proposed, which enable their integration into the structure of a building, notably as exterior cladding.

[0004] Document EP2994940 describes a white photovoltaic module comprising a multilayer stack on the light incident side of the photovoltaic conversion layers which serves as an interferential filter arranged to transmit a certain portion of incident light, notably in the infrared range, while reflecting the rest, notably in the visible range.

[0005] This multilayer stack comprises alternating layers of substantially transparent lower and higher refractive index materials, deposited by sputtering. The lower refractive index material is typically SiO_x, and the higher refractive index material is either Ti02, Nb₂0s or Ta₂0s. For reasons of material costs and deposition rates, T1O2 and Nb₂0s are strongly preferred over Ta₂0s. Furthermore, Ta20s has a lower refractive index than T1O2 and Nb20s, which thus requires thicker layers, further increasing production costs (due to long deposition times) and material costs (due to large quantities of Ta20s being required). [0006] However, since T1O2 and Nb₂0s are photoreduced by UV light, these layers can discolor if they are not exposed to oxygen, which permits the reoxidation of photo-reduced metal ions. As a result, conventional encapsulation techniques are unsuitable, since they hermetically seal the multilayer stack. As a result, such modules are relegated to uses not requiring fully-hermetic front-side encapsulation.

[0007] Other documents disclosing such multilayer stack interference filters in the same or similar roles include US2017/123122 and US2017/033250.

[0008] The aim of the present invention is thus to at least partially overcome the above-mentioned drawbacks of the prior art, and thereby to propose a layer assembly for a photovoltaic module, which comprises such an optical filter which does not suffer discoloration in service.

Disclosure of the invention

[0009] More specifically, the invention relates to a layer assembly (i.e. a stack of layers) for a photovoltaic module according to claim 1. This layer assembly comprises a front sheet on the light incident side of said layer assembly, i.e. the side intended to be facing towards the light source when in use, an optical filter comprising at least one layer containing niobium oxide or titanium oxide, and a resin-based encapsulation layer disposed between said optical filter and said front sheet and in intimate contact (i.e. direct contact) with said optical filter.

[0010] According to the invention, the front sheet has an oxygen permeability of at least 10 cm³/(m².24hr.atm), preferably at least 30 cm³/(m².24hr.atm), preferably at least 70 cm³/(m².24hr.atm), further preferably at least 100 cm³/(m².24hr.atm), further preferably at least 200 cm³/(m².24hr.atm), further preferably at least 300 cm³/(m².24hr.atm), further preferably at least 350 cm³/(m².24hr.atm), and the encapsulation layer contains a proportion of free radical scavengers. This permeability is measured at 20°C, and increases with temperature.

[0011] By incorporating free radical scavengers into the base resin of the encapsulation layer and permitting oxygen to penetrate through the front sheet, discoloration and darkening of the optical filter due to photoreduction is eliminated without resorting to using expensive materials such as tantalum oxide in the optical filter. As a result, PV modules incorporating the layer stack of the invention are rendered suitable for installation on structures, while avoiding use of tantalum oxide and thus keeping material and processing costs low.

[0012] Advantageously, said free radical scavengers comprise at least one hindered amine light stabiliser. This, or other free radical scavengers, may be present in said front encapsulation layer in a concentration of between 0.05 wt% and 2 wt%, preferably between 0.1 wt% and 0.5 wt%.

[0013] Advantageously, said encapsulation layer may also comprise pigment particles, which serve to render the encapsulation layer opaque and/or coloured (e.g. white, terracotta), and thus serve to hide the underlying patterning, connectors etc. from view.

[0014] Advantageously, said front sheet is made of oxygen-permeable polymer such as ETFE (“Tefzel”, “Dyneon”, “Norton” etc), PMMA (“Diakon”, “Lucite”, “Plexiglas” etc.), PVF (“Tedlar” etc), THV (“Dyneon” etc) or ECTFE (“Halar” etc.).

[0015] Advantageously, said front sheet may have a thickness ranging between 50pm and 200pm, preferably between 75pm and 125pm.

[0016] The layer assembly of the invention may be situated on a light incident side of a PV conversion device (i.e. one or more NP, PN, NIP or PIN junctions adapted to convert light energy into electrical energy), so as to constitute a PV module. In such a case, the optical filter may be situated directly upon said photovoltaic conversion device. Alternatively, it may be situated indirectly thereupon, with one or more intermediate layers disposed in between.

[0017] The layer assembly of the invention may also form at least part of a front cover for a photovoltaic module, suitable to be laminated to a PV conversion device or even to a complete, pre-existing PV module, for instance by means of a further encapsulation layer. In such a case, a transparent substrate adjacent to the optical filter may also be provided, if desired. [0018] In the case in which the front cover is laminated to a pre-existing PV module, this results in the front sheet of the pre-existing PV module becoming an internal front sheet upon which is affixed said front cover.

Brief description of the drawings

[0019] Further details of the invention will appear more clearly upon reading the description below, in connection with the following figures which illustrate:

- Figure 1 : a schematic cross-sectional view of a layer assembly for a photovoltaic module, according to the invention;

- Figures 2-4: schematic cross-sectional views of variants of photovoltaic modules each comprising a layer assembly according to the invention;

- Figure 5: a schematic representation of a building structure provided with a photovoltaic module according to the invention; and

- Figure 6: a graph of experimental results plotting reflection against light exposure time of three photovoltaic modules comprising optical filters containing niobium oxide.

Embodiments of the invention

[0020] It should be noted in the following that, unless explicitly stated that a particular layer is disposed directly on the adjacent layer, it is possible that one or more intermediate layers can also be present between the layers mentioned. As a result, “on” should be construed by default as meaning “directly or indirectly on”. Furthermore, patterning of certain layers, connectors and so on are not represented since they are well-known to the skilled person.

[0021] Figure 1 illustrates a layer assembly 1 for a photovoltaic (PV) device, according to the invention.

[0022] The layer assembly 1 comprises a front sheet 3 arranged on the light incident side thereof, i.e. the side which is intended to face the light source when in use (as indicated by the sun symbol), which protects the underlying layers from environmental influences, mechanical stresses and so on as is generally known. The front sheet is affixed to an optical filter 7 by means of an encapsulation layer 5, which is in direct contact with the optical filter 7 and with the front sheet 3. Encapsulation layer 5 is typically formed from a base resin which is thermoplastic and/or cross-linkable, as is generally known, and to which additives are added during manufacture as will be explained below.

[0023] Optical filter 7 comprises one or more layers, and may for instance be an interference filter comprising a multilayer stack of several layers of alternating higher and lower refractive index transparent materials such as disclosed in EP2994940, US2017/123122 or US2017/033250 (herein incorporated by reference in their entireties, insofar as the optical filter is concerned), intended to allow infrared and some visible light to pass, and to reflect some or all wavelengths of visible light in order to appear coloured to a viewer observing the light-incident side of the layer stack 1. Alternatively, optical filter 7 may comprise a single layer.

[0024] At least one of the layers of said optical filter 7 comprises titanium dioxide (T1O2) and/or niobium oxide (Nb20s).

[0025] As mentioned above, in the presence of natural light and the absence of oxygen, both T1O2 and Nb₂0s are reduced, forming radicals which discolour and darken the T1O2 or Nb20s.

[0026] In order to prevent this, two particular measures are taken in combination.

[0027] Firstly, front sheet 3 has sufficient oxygen permeability to enable oxygen to penetrate, while remaining waterproof. In order to achieve this, the front sheet 3 is constructed of oxygen permeable polymer such as ethylene tetrafluoroethylene (ETFE), ethylene chlorotrifluoroethylene (ECTFE), THV (a polymer of tetrafluoroethylene, hexafluoropropylene and vinylidene fluoride), polyvinyl fluoride (PVF) or poly(methyl methacrylate) (PMMA). Other polymers are also possible. The thickness of the front sheet 3 can be tuned to give the desired oxygen permeability while retaining resistance to the penetration of water. The minimum oxygen permeability is 10 cm³/(m².24hr.atm) at 20°C, preferably at least 30 cm³/(m².24hr.atm) or even at least 70, 100, 200 or even at least 300 or 350 cm³/(m².24hr.atm) at 20°C, which can be achieved with typical 50pm-200pm front sheet 1 thicknesses of commercially-available polymers as mentioned above. These values are measured at 20°C and at atmospheric pressure, and it should be noted that atmospheres (atm) and bar (10⁵ Pascals) can be interchanged in the units used here for oxygen permeability since the difference therebetween is trivial and can be ignored.

[0028] Typical oxygen permeabilities for commercially-available polymers are reported in the table below, and are taken from various datasheets and sources. The manufacturers have been anonymised for the purposes of this specification, and layer permeabilities are either as reported or as-calculated based on the permeability coefficients reported. The various types of each polymer are supplied by different manufacturers and indicate the variations which exist between otherwise-similar polymer preparations:

[Table A] [0029] The oxygen permeabilities reported in the above table increase with increasing temperature, and since PV modules heat up during use, an oxygen permeability which is sufficient at 20°, 25° or similar will by definition be adequate at higher temperatures. At 20°C the permeabilities will be slightly, but inconsequentially, lower, than those reported in the table for slightly higher temperatures.

[0030] The second measure taken is the incorporation of free radical scavengers in the encapsulant layer 3. Generally, such additives are derivatives of 2, 2,6,6, - tetramethylpiperidine, and are known as hindered amine light stabilisers (HALS). Other free radical scavengers are also possible, and serve to reduce the quantity of peroxy radicals and to prevent the formation of unstable peroxides which lead to discoloration of the underlying optical filter layer(s) 7.

[0031] In the case of HALS, examples of such are Tinuvin 770, Tinuvin 292, Tinuvin 123 and Hostavin 3058. These references refer to specific proprietary compositions which do not change over time, new formulations being given new reference numbers by their manufacturers and thus assuring repeatability of the invention for the skilled person. Furthermore, many other examples of HALS are known to the skilled person from the literature, and need not be related exhaustively here. For instance, such substances are disclosed in US6214995, US9045480, US5145893, US5679794,

US4972009, all of which are herewith incorporated by reference insofar as they concern HALS substances.

[0032] This additive comprises one or more such substances, and is incorporated in the encapsulant layer 3 in a concentration between 0.05 wt% and 2 wt%, preferably between 0.1 wt% and 0.5 wt% (wt% being“weight percent”, i.e. percentage by weight, which is interchangeable in practice with the other commonly-used measure phr, which corresponds to “parts per hundred resin”, due to the difference between the two metrics being inconsequential when dealing with such small additive concentrations. As such, the difference between phr and wt% is trivial and can be ignored).

[0033] The base resin of the encapsulation layer 5 can be any convenient thermoplastic and/or cross-linkable polymer, such as Ethylene-vinyl acetate (EVA), silicone, urethane, polyvinyl butyral (PVB), thermoplastic silicone elastomer (TPSE), ionomers, polyolefins (PO), thermoplastic polyurethane (TPU), or any other convenient polymer. [0034] The material of the encapsulation layer 5 may also comprise further UV absorbers or stabilisers such as hydroxybenzophenone, hydroxyphenylbenzotriazole, oxanilides, benzophenones, benzotriazoles or hydroxyphenyltriazines.

[0035] The encapsulation layer 5 may also comprise pigmentation particles such as titanium oxide or zinc oxide particles for a white colour, various iron oxides for yellow, orange, red and brown colours (for instance Fe203 for red ochre, or FeO(OH) for yellow), complex sulphur-containing sodium silicates for blue colours, or any convenient other pigments. At least 50% of the pigment particles 21 typically have a size ranging from 100 nm to 1 pm, most notably from 300-700 nm, and most particularly from 400-600 nm, and may be provided in concentrations ranging from 0.01 to 10 parts per hundred (pph) of the resin serving as the basis for the front encapsulation layer 13. More particularly, 0.1 to 5 pph of pigment particles 21 can be used.

[0036] In respect of the manufacture of the encapsulant layer 5, the required quantity of additives can simply be mixed in with the base resin or resin precursor which will form the encapsulant layer 5. This can then be extruded as normal, without any special equipment or techniques.

[0037] The combination of an oxygen-permeable front sheet 3 and encapsulant 5 containing free radical scavengers in direct contact with the optical filter 7 allows oxygen to penetrate through the front sheet 3 and encapsulant 5 and reach the optical filter 7. This oxygen, in combination with the free radical scavengers, causes the photoreduced ions from T1O2 and/or Nb₂0s to re- oxidise immediately upon their formation upon UV light exposure, thereby preventing discoloration of the T1O2 and/or Nb₂0s layers. In essence, the presence of free radical scavengers in the encapsulation layer 5 is not primarily for the benefit of the stability of the encapsulation layer itself, but rather to protect the underlying optical filter 7 and render it colour stable.

[0038] In terms of structure, the layer assembly 1 may be manufactured as such and thereby constitute a front cover for a photovoltaic module, which can be laminated on to the light incident side of a photovoltaic conversion device 11 by means of a further encapsulation layer 9 of EVA or any other convenient encapsulant material such as those mentioned previously, so as to form a photovoltaic module 17 as illustrated in figure 2. In such a case, an optional, preferably transparent, substrate (not illustrated) may be provided, upon which the optical filter 7 is deposited.

[0039] The photovoltaic conversion device 11 typically comprises one or more PV cells comprising NIP, PIN, NP or PN junctions, patterned and interconnected as is generally known, these junctions being arranged to convert light energy into electrical energy. The PV cells may be based on thin-film silicon, crystalline silicon, germanium, perovskite, dye-sensitised cells, or any other type of PV technology adapted to generate electrical power from light impinging on the light-incident side of the PV module 17 and passing into the PV cells.

[0040] On the rear side of the photovoltaic conversion device 11 is situated a backsheet 15, which may be made of metal, glass, ceramic, polymer or any other convenient material. If required, a rear encapsulant layer 13, again of EVA or other convenient material, may affix the back sheet 15 to the PV conversion device 11 in the case in which the back sheet 15 is not self- adhesive.

[0041] As a result, the PV module 17 can simply be manufactured by conventional lamination techniques, with the front cover being placed directly adjacent to the further encapsulation layer 9, itself situated on the light-incident side of the PV conversion device 11 , the module 17 then being assembled by an application of heat and pressure in a lamination device. This latter can be a vacuum bag laminator, a hot press laminator, a roller-based laminator, or similar.

[0042] Figure 3 illustrates another variant of a PV module 17 incorporating a layer assembly 1 according to the invention.

[0043] This variant differs from that of figure 2 in that, rather than being provided as a front cover laminated onto the light incident side of the PV conversion device 11 , the one or more layers of optical filter 7 are deposited upon the PV conversion device 11 e.g. by PVD, sputtering, or similar, as an extra step of manufacture thereof. The front sheet 3 is then subsequently laminated on to the light incident side of the optical filter 7 by means of the encapsulant layer 5 in the same lamination step as the assembly of the backsheet 15, or alternatively in a separate lamination step.

[0044] Figure 4 illustrates yet another variant of a PV module 17 incorporating a layer assembly 1 according to the invention.

[0045] This variant differs from that of figure 2 in that the layer assembly 1 is provided as a cover sheet which is laminated onto the front sheet 19 of a pre- existing PV module 23 by means of a further encapsulation layer 21. In consequence, the resulting PV module comprises not only the sequence of elements 9, 11 , 13 and 15 as described above, but also an internal front sheet 19 (corresponding to the original front sheet of the pre-existing PV module 23), and an encapsulation layer 9, 21 either side thereof. This enables the advantages of the optical filter 7 and the encapsulant layer 5 of the invention to be applied to pre-existing, pre-fabricated PV modules.

[0046] It is re-iterated that, in all of the above embodiments, the presence of further intermediate layers, whether they are functional or non-functional, is not excluded, except where specified in respect of the relationship between the front sheet 3, encapsulant 5 and optical filter 7. In particular, when the layer assembly 1 of the invention is intended to be used as a cover sheet, a transparent substrate of e.g. glass, polymer or similar, may be provided upon which the optical filter 7 is deposited by e.g. sputtering, the front sheet 3 being subsequently laminated thereupon by means of the encapsulant 5.

[0047] On a related point, it should be noted that, during manufacture, encapsulant layer 3 may be formed from multiple sheets of encapsulant material and/or encapsulant material precursor, which form a unitary layer of encapsulant 3 during lamination. In the case of multiple, thinner sheets of encapsulant material being placed in the laminator, at least the sheet directly in contact with the optical filter 7 should contain free radical scavengers as an additive; any pigment particles present may be provided in any or all layers.

[0048] Furthermore, front sheet 3 may be structured, textured, be printed with a pattern, colour or texture, may have a graphic film affixed thereupon, or may comprise further layers situated on the light incident side thereof. Also, the module does not need to be flat, but can be curved or shaped as desired.

[0049] Figure 5 illustrates a photovoltaic module 17 of any type described above mounted on the roof of a building 35. Alternatively, the PV module 1 can be mounted to an exterior wall, or integrated into the structure of the wall and/or roof, e.g. as cladding. In general terms, the PV module 1 can be mounted on or in the structure of the building 35.

[0050] Figure 6 represents a graph of results of a light stability test carried out on three different white PV modules, each constructed according to the teaching of EP2994940. In each of these modules, the optical filter comprises a multilayer stack of twenty-one alternating SiO_x and Nb₂0s layers having a total thickness of 1.6pm, deposited by sputtering on a PET substrate and then laminated on the front glass of standard commercially-available PV modules (i.e. with the construction of figure 4, with an additional PET substrate between layers 7 and 21), with front sheets and EVA-based encapsulants according to the following table:

* the ETFE used is the type known as“Norton” available from Saint-Gobain.

[Table 1]

[0051] The encapsulants were compounded on a twin-screw extruder at 95°C, and all encapsulants were based on EVA with a peroxide crosslinking agent. Furthermore, in addition to the additives mentioned in table 1 , they contained 0.05 phr of Ti0₂-based nanoparticles as light diffusive agents. The combination of the multilayer optical filter 7 and the nanoparticles gave the modules a white appearance.

[0052] The graph of figure 6 represents a graph showing the reflection for the three modules of types A-C after various times of exposure to light at 60°C on a QUV accelerated weather chamber using UVA lamps with an irradiance of 0.8W/m² at 340nm. The optical filter 5 was adapted to reflect 90% of visible light and to transmit substantially 100% of light in the infrared range.

[0053] Module type A shows a significant darkening after 500 hours exposure, as evidenced by the >45% reduction in reflection, indicating colour degradation and darkening. Since module type A uses an entirely impermeable front sheet 3 made of glass in combination with free radical scavengers in the encapsulant 5, this illustrates clearly that the use of free radical scavengers alone is entirely insufficient to prevent discoloration of the optical filter 7.

[0054] Module type B also has an approximately 15% reduction in reflectivity after 1000 hours of exposure, which is clearly unacceptable for commercial use. Since this module has an oxygen-permeable EFTE front sheet 3 with an oxygen permeability of at least 350 cm³/(m².24hr.atm) at 20°C but no free radical scavengers in the encapsulant 5, discoloration is slower than for the type A module. However, this clearly indicates that oxygen penetration through the front sheet 3 alone is not sufficient to guarantee colour stability.

[0055] Module type C, on the other hand, has constant reflection even after more than 3000 hours of exposure, indicating no discoloration. Since this module comprises an oxygen-permeable EFTE front sheet 3 as above and also free radical scavengers in the form of HALS in the encapsulant 5, this clearly shows the synergy between these two measures, and illustrates the surprising and unexpected technical effect of their use in combination. In essence, it is clear that the combination of these two measures is far greater than the sum of the effects of each measure alone: on the basis of the results obtained with the type A and type B modules, one might expect discoloration of the type C module to still occur but at a slower rate. However, and quite unexpectedly, discoloration is entirely prevented, at least on the timescales tested, by the combination of the two measures.

[0056] In another set of tests, four further white samples were fabricated and their light stability was tested at 70°C and 20% relative humidity on a QSun accelerated weather chamber using xenon lamps with an irradiance of 0.8W/m² at 340nm wavelength.

[0057] In each case, the samples were prepared by laminating the same 21 -layer optical filter 7 as described above in connection with the previous tests to a glass substrate by means of a commercial EVA-based encapsulant material. To the light-incident side of the optical filter 7, the encapsulant 5 and front sheet 3 prepared as described above with peroxide and T1O2 nanoparticles in their composition in addition to the additives as mentioned in the table below:

* the ETFE used is the type known as“Norton” available from Saint-Gobain.

[Table 2]

[0058] Again, this clearly shows that with an impermeable glass front sheet 3, the Nb₂0₅-containing optical filter 7 discolors and darkens rapidly, even after only 500h exposure. Again, the combination of an ETFE front sheet 3 with HALS additives in the encapsulant 5 entirely eliminates darkening up to at least 2000h of exposure. The putative increase in reflectance of the types F and G samples is within measurement error and is hence an artefact of measurement accuracy. The ETFE front sheet used in these tests is the same as used in those of Table 1.

[0059] In a yet further series of tests, five more white samples were fabricated and tested similarly to those of table 2, the differences being in the nature of the base resin of the encapsulant 5. In these samples, the encapsulant 5 is thermoplastic olefin (TPO) based, and various base resins were tested, as described in the table below, in which the base resins are identified by their manufacturer references (which indicate a specific, unchanging, composition):

* the ETFE used is the type known as“Norton” available from Saint-Gobain.

[Table 3]

[0060] Again, the results show clearly that, even for various TPO encapsulant base resins, discoloration and darkening occurs with an oxygen permeable ETFE front sheet 3 (which is again the same as used in those of Table 1) and in the absence of free radical scavengers in the encapsulant 5. Only in the presence of both the free radical scavengers and the oxygen permeable front sheet 3 is darkening prevented. Again, the apparent increase in reflectance is an artefact of measurement accuracy.

[0061] Although the invention has been described in terms of specific embodiments, variations thereto are possible without departing from the scope of the invention as defined in the appended claims.

Claims

1. Layer assembly (1) for a photovoltaic module (17) comprising:

- a front sheet (3) arranged on a light incident side of said layer assembly (1);

- an optical filter (7) comprising at least one layer containing niobium oxide or titanium oxide,

- an encapsulation layer (5) comprising a base resin, said encapsulation layer (5) being disposed between said optical filter (7) and said front sheet (3) and in intimate contact with said optical filter (7);

characterized in that:

- said front sheet (3) has an oxygen permeability of at least 10 cm³/(m².24hr.atm) at 20°C, and

- said encapsulation layer (5) comprises free radical scavengers.

2. Layer assembly (1) according to claim 1 , wherein said free radical scavengers comprise at least one hindered amine light stabiliser.

3. Layer assembly (1) according to claim 1 or 2, wherein said free radical scavengers are present in said front encapsulation layer (5) in a concentration of between 0.05 wt% and 2 wt%, preferably between 0.1 wt% and 0.5 wt%.

4. Layer assembly (1) according to any preceding claim, wherein said encapsulation layer (5) comprises pigment particles.

5. Layer assembly (1) according to any preceding claim, wherein said front sheet (3) is made of oxygen-permeable polymer.

6. Layer assembly (1) according to the preceding claim, wherein said oxygen- permeable polymer is ETFE, PMMA, THV or PVF or ECTFE.

7. Layer assembly (1) according to one of claims 5-6, wherein said front sheet (3) has a thickness ranging between 50pm and 200pm, preferably between 75pm and 125pm.

8. Layer assembly (1) according to any preceding claim, wherein said oxygen permeability is at least 30 cm³/(m².24hr.atm), preferably at least 70 cm³/(m².24hr.atm), further preferably at least 100 cm³/(m².24hr.atm), further preferably at least 200 cm³/(m².24hr.atm), further preferably at least 300 cm³/(m².24hr.atm), further preferably at least 350 cm³/(m².24hr.atm).

9. Photovoltaic module (17) comprising a photovoltaic conversion device (11) provided with a layer assembly (1) according to any preceding claim situated on a light incident side thereof.

10. Photovoltaic module (17) according to the preceding claim, wherein said optical filter (7) is situated directly upon said photovoltaic conversion device (11).

11. Front cover for a photovoltaic module (17), said front cover comprising a layer assembly (1) according to any of claims 1-8.

12. Photovoltaic module (17) comprising a photovoltaic conversion device (11) upon which is situated a front cover according to claim 11.

13. Photovoltaic module (17) according to the preceding claim, wherein said front cover is affixed to said photovoltaic conversion device (11) by means of a further encapsulation layer (9).

14. Photovoltaic module (17) according to claim 13, further comprising an internal front sheet (19) upon which is affixed said front cover.

15. Building (35) comprising at least one photovoltaic module (17) according to one of claims 9-10 or 12-14.