WO2015078508A1

WO2015078508A1 - Method for producing a photovoltaic device with a textured surface

Info

Publication number: WO2015078508A1
Application number: PCT/EP2013/075065
Authority: WO
Inventors: Ko Hermans; Michelle Elizabeth Seitz
Original assignee: DSM IP Assets BV
Current assignee: DSM IP Assets BV
Priority date: 2013-11-29
Filing date: 2013-11-29
Publication date: 2015-06-04
Anticipated expiration: 2016-05-29

Abstract

A method of forming a photovoltaic device is disclosed. The method comprises the steps of fixing components of the photovoltaic device together, said components comprising a front cover and a back cover, and forming a texture on the front cover or the back cover by bringing a polymeric or polymerizable material on the front cover or the back cover in contact with a durable mould, wherein the steps of fixing components of the photovoltaic device together and forming a texture on a surface of the photovoltaic device are performed simultaneously. Further, a laminator is disclosed comprising a durable mould, which durable mould contains a relief texture and is placed inside a laminator, with the relief texture facing the surface of the photovoltaic device that needs to be textured.

Description

METHOD FOR PRODUCING A PHOTOVOLTAIC DEVICE WITH A

TEXTURED SURFACE

Field of the Invention

The invention pertains to a method of forming a photovoltaic device having a textured external surface and to an apparatus for performing said method.

Background

Texturing of external surfaces of photovoltaic elements is known in the art. A photovoltaic device possessing an external textured surface may possess an increased efficiency over a photovoltaic device without such a textured surface. The efficiency improvement is the result of improved anti- reflection and/or light trapping qualities of the textured surface. Whether the texture provides an anti-reflection and/or light trapping effect, and the

magnitude of such effect, is dependent on the geometry of the texture.

In addition to being affected by the geometry of the texture, the magnitude and longevity of the anti-reflection and/or light trapping effect provided by a texture is dependent on the accuracy with which the texture is formed and the durability of the texture. A texture that is a poor copy of the ideal texture geometry as designed, such as the texture present on a mould used to form the texture, will provide a lesser effect than a texture that is produced more accurately. Furthermore, a lesser effect over time is

experienced for a texture that, although initially formed accurately by the manufacturing process, is subject to degradation in the form of warping, mechanical damage, fouling, or a reduction in its transparency compared to a more durable texture.

Textures may be formed from glass or from a polymeric material. Although hot-rolling of glass is known as a method of texturing a glass front cover of a photovoltaic device, the resulting relief textures are a poor representation from their intended shape, especially when sub-millimeter sized relief textures are desired. There are e.g. several ways to apply these textures into a polymeric material. One way is to make them directly into a thermoplastic polymeric sheet, which can be used as a front cover, by for example hot-rolling the texture into the sheet at a temperature above the softening point of the material. However, the material still resists mechanical deformation and has the tendency to deform back to its flat state after leaving the hot-roller or mould. Consequently, the textures that can be obtained via this method are often an insufficient copy of the actual texture that was on the hot-roller or mould. The performance increase of the photovoltaic modules by such a non-ideal texture is low.

Other options for texturing the external surface of a photovoltaic device include curing thermoset materials on a durable film to form a textured sheet. The textured sheet formed from such a process can then be applied to the photovoltaic device with the aid of an appropriate adhesive. See, for example, WO20101 15954. Such a textured sheet requires separate

manufacturing processes. Additionally, thermoset materials, such as UV-cured materials, may exhibit reduced outdoor durability compared to thermoplastic materials.

US20120282437 mentions texturing the external surface of a photovoltaic device during a lamination process. A coated fiberglass fabric is used to texture a fluoropolymer that is present on an external surface of a photovoltaic device. The coated fiberglass is removed after the lamination step, leaving a textured fluoropolymer layer. However, the textures formed are of poor sharpness and quality.

An improved process to produce a photovoltaic device having a texture on an external surface is therefore desirable.

Summary

The known methods of producing a cover of a photovoltaic device require a separate processing step, exhibit reduced outdoor durability, and/or produce textures that are of poor sharpness or quality. For example, a pre-formed textured thermoplastic polymeric sheet, which is used as front cover, may not withstand the lamination step of the photovoltaic device assembly. In the lamination step the various layers of the photovoltaic device assembly are laminated together in a laminator machine. The lamination step requires elevated temperatures and pressures. The elevated temperatures and pressures that are required for this step will deform the texture, and thereby reduce its performance.

Another option is to make the textures into a polymer sheet, and applying said sheet to the front cover after the lamination step. Although this solves the issue that a textured polymeric sheet deforms during lamination, it requires an additional processing step.

In accordance with the invention, such problems can be overcome by utilizing a durable mould to texture a cover of a photovoltaic device while simultaneously fixing components of the photovoltaic device together.

The first aspect of the instant claimed invention relates to a method for forming a photovoltaic device. After performing the method, a photovoltaic device comprising a textured surface on the front cover or the back cover is obtained. The method of forming a photovoltaic device comprises the steps of fixing components of the photovoltaic device together, said

components comprising a front cover and a back cover of the photovoltaic device, and forming a texture on the front cover or back cover of the

photovoltaic device by bringing a material, said material being polymeric or polymerizable, on the front cover or the back cover in contact with a durable mould. The steps of fixing together and forming a texture are performed simultaneously.

In a second aspect of the instant claimed invention, a texture is applied to a photovoltaic device during the production of said device by placing a durable mould, which contains a relief texture, in a laminator, with said relief texture facing the surface that needs to be textured. During the laminating procedure, which involves elevated temperatures and pressure, the relief texture is imprinted into or onto an external surface the photovoltaic device at the same time as the single components of the photovoltaic device (i.e. at least the front cover, cells, encapsulent and back cover) are laminated together.

A third aspect of the instant claimed invention relates to a laminator for laminating together the components of a photovoltaic device. The laminator comprises a durable mould facing a surface of the photovoltaic device.

Brief Description of the Drawings

Figure 1 is a schematic representation of a cross-sectional view of a textured cover of a photovoltaic device.

Detailed Description

There are several types of photovoltaic devices. In principle, one can distinguish between thin film photovoltaic devices and wafer based photovoltaic devices. The main difference between these two is the thickness of photovoltaic active layer which in the case of thin film devices is obviously thinner (e.g. 0.1 - 3 micron) than for wafer based devices (e.g. 100-200 micron). Although most of the production process for these two different types of devices is completely different, since, for example, different production methods are required to apply either thin films or cut relatively thick wafers, they both have at least one production step in common. This common step involves fixing the front cover of the photovoltaic device to the back cover. The other components of the photovoltaic device, such as the photovoltaic cells and electrodes, are typically fixed in between said covers during this production step.

The method of the invention can be used on all types of photovoltaic devices. These devices can be based on thin film photovoltaic technologies such as CdTe, CIGS, a-si, a-si/ c-si or OPV. Also, photovoltaic devices based on multi-crystalline or mono-crystalline cells, or any other wafer based technology, can be used.

According to a first aspect of the instant claimed invention, the step of forming a texture on the front cover or the back cover of the photovoltaic device and the step of fixing components of the photovoltaic device together are performed simultaneously. In an embodiment, this is done by incorporating a durable mould into the apparatus used to fix together the front cover and back cover of the photovoltaic device such that components of the photovoltaic device can be fixed together while a texture is formed.

By simultaneously it is meant that at least part of one step is carried out while also carrying out at least part of the other step. In an embodiment, the elevated temperatures and/or pressures that are typically necessary for fixing components of the photovoltaic device together are also utilized for forming a texture on one or both of the front and back cover. The steps of fixing together and forming a texture are thus performed

simultaneously. In addition to the benefits of eliminating one or more process steps relating to forming a texture and securing the texture to the surface of the photovoltaic device, such a simultaneous process additionally enables the use of thermoplastic materials that deform at the elevated temperatures and/or pressures typically necessary for fixing components of the photovoltaic device together.

The most common method in current commercial application for fixing together components of a photovoltaic device is a lamination process. During a lamination process, the front and back cover are fixed together by using an encapsulent and a laminator.

A lamination process makes use of an encapsulent. The encapsulent is basically a material that joins the front cover and the back cover together. The material is called an encapsulent because often it not only connects the front and back cover, but also encapsulates the solar cells and the electrodes which are placed in between the front and back cover, thus fixing their relative positions and protecting them from direct exposure to air. The encapsulent is usually a polymer such as for example ethylene vinyl acetate (EVA), poly vinyl butyral (PVB), silicone, thermoplastic poly urethane (TPU) or an ionomer.

In a lamination process the components of the photovoltaic device are fixed together using a laminator. The laminator is the equipment which is used to make sure that the front cover and the back cover are joined together at the required processing conditions for a specific encapsulent, and without any air-bubbles entrapped in the encapsulent. There are several types of laminators available (e.g. flatbed laminator, roll laminator), but they all involve at least some form of pressure, to avoid the air-bubbles, and heating, for softening and/or curing of the encapsulent. Typical temperatures are from about 130 to 170 °C and depend on the type of encapsulent and the components of the photovoltaic device. Typical pressures are from about 0.05 MPa to 0.2 MPa. The exact processing conditions depend on the type of encapsulent, and potentially the other components of the photovoltaic device.

The required processing conditions (e.g. the temperature, pressure and time) for lamination restrict the materials that can be used for photovoltaic device components. Especially components (other than the encapsulent) made from materials that soften at the laminating temperature cannot withstand lamination without deterioration of their shape since the involved pressure deforms their original or intended shape and consequently destroys their intended function. This severely limits the materials that can be used for certain components.

In an embodiment, the method further comprises raising the temperature to from 130 °C to 170 °C, preferably from 140 °C to 160 °C. In an embodiment, the method further comprises applying a pressure of from 0.05 MPa to 0.2 MPa. The high temperatures and pressures typical of an injection moulding process are not possible when fixing components of the photovoltaic device together because they will damage the components of the photovoltaic device.

There are several types of laminators that could be used for carrying out the invention. Examples include a flatbed laminator or roll laminator. In a flatbed laminator, the components of the photovoltaic device are placed against a surface at an elevated temperature and pressure for some time. In a roll laminator, pressure is applied to the covers of the photovoltaic device by one or more rolls that pass over the cover of the photovoltaic device at elevated temperature and pressure. For example, during a typical production process of wafer based photovoltaic devices, the front and the back cover are joined together by using ethylene vinyl acetate (EVA). This is typically done in a flatbed laminator at a temperature of around 150 °C and 1 bar pressure, difference by using a vacuum, for about 10-20 minutes. The EVA encapsulent, which is typically in the form of one or more sheets of solid material at room temperature, is placed between the front and back cover. At the same time also the photovoltaic cells, electrodes and some other components are placed between the front and back cover. During the lamination the EVA is heated above its softening temperature and at this point starts to stick to both the front and the back cover. The pressure and/or vacuum are used to avoid any air entrapments inside the EVA. After the lamination step, the photovoltaic module is cooled and then removed from the laminator and the front cover and back cover (and all other

components that were placed in between the two covers) have been joined together by a solid layer of air bubble free EVA.

In accordance with the method of the invention, during the fixing of components of the photovoltaic device together, for example by lamination, a texture is formed on the front cover or the back cover of the photovoltaic device by bringing a material, said material being polymeric or polymerizable, on the front cover or the back cover in contact with a durable mould. The polymeric or polymerizable material may form the cover or be present on the surface of the cover, but does not need to be in contact with the front cover or back cover directly; additional intermediate layers between the front cover or back cover and the material may be present, such as adhesives.

There is a vast array of potential names for a mould, including a shim, embossing roll, embosser, engraving roller, stamp, or the like. The mould could be made from any materials that can withstand, without undesired deformation of the relief texture, the lamination process parameters (i.e. the temperature, pressure and time). Preferably the mould is made from a metallic material, such as, for example, nickel. The mould may be rigid or semi-flexible. For example, a mould may be semi-flexible as long as it can sufficiently retain its texture shape during the moulding process. The mould is durable, meaning that it can withstand numerous lamination sequences while producing textures of high quality before

replacement is needed. In a preferred embodiment, the durable mould is capable of functioning for more than one thousand lamination sequences, more preferably more than ten thousand lamination sequences.

The durable mould is used to form a texture on the front cover and/or the back cover of the photovoltaic device. Different relief textures can be used, such as, for example, an array of pyramidal textures (WO03/046617), V- shaped grooves (G.A. Landis, 21 ^st IEEE photovoltaic specialist conference, 1304-1307 (1990)), round pits (P. Sanchez-Friera, IEEE 4^th World Conference on photovoltaic energy conversion, 2156 - 2159 (2006)), or structures consisting of a base and an apex which are connected by n-polygonal surfaces with n being equal to 4 or higher (WO2009059998). Typical texture sizes are from one micron to one millimeter in height. Preferably, the texture sizes are from 10 microns to 100 microns in height.

The durable mould preferably has a continuous texture forming face. By continuous it is meant that there are no gaps in the face that would allow material to pass through the texture forming face of the durable mould.

Forming the durable mould can be carried out in any number of exemplary ways. For instance, in one method a laser ablation process is used wherein a laser is directed to blast away unwanted areas of material from a master. The master is then used to form a metallic mould. Further exemplary processes involve diamond cutting or photo-emulsion processes. The mould is often subject to an electroplating process to form a metallic surface layer, such as a nickel layer.

In an embodiment, the mould comprises a metal surface. In a further embodiment, the metal surface is used to form the texture. In a further embodiment, the metal surface comprises a negative image of a desired texture. The metal surface may be formed from nickel, or any suitable metal. In an embodiment, the durable mould has recesses of from 1 micron to 1 millimeter in depth. In another embodiment, the durable mould has recesses of from 10 microns to 100 microns in depth. The durable mould may be a flat mould or in the form of a cylinder. In either case, the durable mould may be formed from first fabricating a master mould which is then replicated a number of times. The replications are joined together to create a larger mould to complete the full-size mould. The process of joining together the replications will create seams or gaps in the mould which may be visible in the replicated texture. Such seams or gaps will likely constitute a small amount of the overall textured surface and may therefore have little effect on the efficiency of the photovoltaic device.

The texture is formed on the front cover or the back cover from a polymeric or polymerizable material. The material can be the front cover or back cover itself, or on a separate coating or sheet on the front cover or back cover. In an embodiment, the material is supplied as a separate polymeric or polymerizable sheet on the front cover or back cover. In an embodiment, a polymeric or polymerizable sheet on the front cover or back cover adheres to a surface of the front cover or back cover during the step of fixing components of the photovoltaic device together and while the texture is formed in the material via the mould. Additional materials, such as primers or adhesion promoters, may also be used.

In another embodiment, two sheets are provided on the front cover or back cover of the photovoltaic device before forming the texture. A first sheet is a polymeric or polymerizable sheet and a second is a hot melt adhesive, such as EVA. The second sheet is positioned between the first sheet and the front cover or back cover. The texture may be formed from the first sheet or both the first and second sheets. In other embodiments, the material is spray coated, roll coated, slot die coated, screen printed, or otherwise applied to the front cover or back cover.

Most preferably for the invention is that the texture is made from a polymeric material. The material is preferably a thermoplastic polymer. In embodiments, the thermoplastic polymer is a grade of poly ethylene

terephthalate (PET), poly methyl methacrylate (PMMA), polycarbonate (PC) or poly ethylene naphthalate (PEN). Generally, relatively low molecular weight materials are preferred because the materials will generally have a lower viscosity at the temperature when fixing components of the photovoltaic device together. Alternatively the material is a thermo hardening or thermosetting material such as an epoxy, urethane acrylate or polyurethane composition. Another alternative is to use a sol-gel material such as tetraethyl orthosilicate (TEOS) or any non-organic or partially non-organic polymer or polymer precursor, such as for example silicone.

In an embodiment, the thermoplastic polymer is semi- crystalline. In an embodiment, the polymeric material is a blend of acrylic and poly vinylidene fluoride (PVDF), such as Kynar® from Arkema.

Preferably, the polymeric material is a thermoplastic polymer that has a melting temperature around the temperature at which fixing components of the photovoltaic device together is carried out. A thermoplastic polymer with such a melting temperature allows lower pressures to obtain an accurate copy of the mould in the thermoplastic polymer than would be required when using a thermoplastic polymer with a higher melting point. In an embodiment the polymeric material has a melting point of from 120 to 160 °C.

The polymeric materials used could also contain components that are non-polymeric materials which are used for stabilization (e.g. HALS, UV absorber, anti-oxidant, etc .), protection (e.g. anti-scratch coating, anti-fouling coating, etc .), an additional function (e.g. a barrier coating, etc .) or improving processing of the polymer material (e.g. defoaming agent).

In an embodiment, either or both of the durable mould or the polymeric or polymerizable material contain a mould release agent to facilitate demoulding. In an embodiment, either the durable mould or the polymeric or polymerizable material is fluorinated. In an embodiment, the durable mould is fluorinated prior to commencing the step of fixing components of the

photovoltaic device together.

Although the surface which is textured is most preferably made from a polymeric material, this does not necessarily mean that the front cover or back cover of the photovoltaic device should be made from polymeric materials. For example, it is also possible that an additional polymeric coating is applied to a glass front cover of a photovoltaic module and that this polymeric coating is textured according to the disclosed method. Therefore, it can be said that the texture could be formed into or onto a cover of the photovoltaic device.

In an embodiment, the texture is formed by bringing a polymerizable material into contact with the mould. After bringing the

polymerizable material in contact with the mould, the material undergoes polymerization, thereby setting the texture in the material. In an embodiment, the polymerizable material comprises reactive groups, such as acrylate and/or methacrylate groups. In a further embodiment, the polymerizable material comprises an initiator that initiates polymerization. In an embodiment, the initiator is a thermal initiator that is activated at a temperature from 120 °C to 160 °C.

In an embodiment, the viscosity of the material is reduced during the step of forming a texture. The reduced viscosity of the material enables the material to fill the durable mould and form an accurate replication of the mould surface. In an embodiment, the viscosity of the material is reduced to at least 7x10⁶ Pa s for at least 900 seconds. In another embodiment, the viscosity of the material is reduced to at least 2.5x10⁶ Pa-s for at least 300 seconds. By reducing viscosity of the material to such a level for such a time, a high degree of mould fill may be exhibited. In an embodiment, the mould fill is 95% or more, preferably 98% or more, and more preferably 99% or more for a mould with a mean slope of at least 35 degrees. In an embodiment, the mould fill is 95% or more, preferably 98% or more, and more preferably 99% or more for a mould with a mean slope of at least 40 degrees. In an embodiment, the mould fill is 95% or more, preferably 98% or more, and more preferably 99% or more for a mould with a mean slope of at least 45 degrees.

After the material is contacted with the mould and allowed to fill the mould, the viscosity is then increased so that the texture is retained in the material and able to separate from the mould. The viscosity may be increased by reducing the temperature, by cross-linking, or by some combination of both. In an embodiment, the viscosity is increased by crossing the T_g of the material, by forming ionic or hydrogen bond interaction, by crystallization, or by forming covalent bonds. Textures formed using a durable mould may exhibit improved texture definition, mean slope, and depth retention ratios over textures formed from non-durable moulds. The mean slope is defined as the average of the absolute values of all slopes. The texture depth is defined as the depth from a neutral plane of the texture to the apex of a texture. The mean slope retention ratio is defined as the ratio of the mean slope of the formed texture to the mean slope of the mould face.

Reference is now made to Figure 1 . Figure 1 shows a cross- section of a texture on a cover of a photovoltaic device. In Figure 1 , a texture of v-shaped grooves 1 is formed on a cover of a photovoltaic device 2. The texture has faces with slopes 3, 4, 5, 6, 7, 8, 9, and 10. The mean slope of the texture in figure 1 would be determined by taking the absolute values of all slopes 3, 4, 5, 6, 7, 8. 9 and 10. The texture depth is indicated by dimension 1 1 .

In an embodiment, the mean slope of the texture on the mould face is 35 degrees or more, preferably from 35 to 60 degrees. In an

embodiment, the mean slope of the texture on the mould face is at least 45 degrees, preferably from 45 to 60 degrees.

Textures formed in accordance with the invention may have a mean slope of 35 degrees or more, preferably from 35 to 60 degrees. In an embodiment, the mean slope of the textures formed is at least 45 degrees, preferably from 45 to 60 degrees. Furthermore, the mean slope retention ratio may be 90% or greater, preferably 95% or greater.

Moreover, a durable mould allows for improved texture depth retention ratios at higher mean slopes than with the use of a non-durable mould. In an embodiment, the texture depth retention ratio, defined as the ratio of the texture depth of the formed texture to the texture depth of the mould, is 90% or greater. In another embodiment, the texture depth retention ratio is 90% or greater and the mean slope of the formed texture is 35° or greater. In another embodiment, the texture depth retention ratio is 95% or greater and the mean slope of the formed texture is 40° or greater. Another embodiment of the present invention is a laminator suitable for laminating a front and back cover of a photovoltaic device together, which laminator comprises a durable mould; said durable mould contains a relief texture and is placed inside the laminator, with the relief texture facing the surface of the photovoltaic device that needs to be textured. Preferably, the durable mould is flat on one side, allowing for straight-forward installation in a flatbed laminator. In an embodiment, the durable mould is flat and placed in a flatbed laminator.

Examples

Example 1 :

A nickel mould containing a relief texture is placed inside a flatbed laminator. A stack of a crystalline PET front cover, a first sheet of PVB encapsulent, flexible CIGS cells, a second sheet of PVB encapsulent and a PET back cover are placed in their respective order on top of the nickel mould. The flat-bed laminator is closed and the nickel mould and the stack of components are heated for e.g. 15 minutes to a temperature of 170 °C while maintaining a vacuum in the laminator and a pressure of 1 bar (atmospheric) on nickel mould and the components. During the lamination process the relief from the nickel mould is pressed into the PET front cover. After opening the laminator, a photovoltaic device with a textured front cover is obtained.

Example 2:

A nickel mould containing a relief texture is placed inside a flat- bed laminator. A stack of a resin coated glass front cover (with the resin facing the nickel mould), a first sheet of EVA encapsulent, poly-crystalline cells, a second sheet of EVA encapsulent and a Tedlar® back cover are placed in their respective order on top of the nickel mould. The flat-bed laminator is closed and the nickel mould and the stack of components are heated for e.g. 15 minutes to a temperature of 150 °C while maintaining a vacuum in the laminator and a pressure of 1 bar (atmospheric) on nickel mould and the components. During the lamination process the relief from the nickel mould is pressed into the resin coating on the glass front cover and the resin is hardened by heat from the laminating step. After opening the laminator, a photovoltaic device with a textured front cover is obtained. Example 3:

A nickel mould containing a corner cube relief texture as described in WO2009/059998 is placed inside a laminator. A 3 mil thick film of PVDF (P/N P-00017-7, Welch Fluorocarbon, Inc., Dover, NH, USA) is placed in a laminator. A standard lamination process as when EVA is the encapsulent is carried out. A vacuum is applied substantially equally on both sides of the film. The temperature is gradually raised and, after some initial heating the vacuum on top of the film is turned off leaving a pressure of approximately 1 bar on the film. The film is heated until a temperature of 150 °C is reached and then the temperature is held for a few minutes. The film is cooled while still under pressure and then removed from the laminator. The total process time was 15 minutes with a maximum temperature of 150 °C. A textured polymeric film of high definition is obtained.

Although not specifically carried out, a similar process could be performed while fixing the components of the photovoltaic device together and the formed texture could be secured to a surface of the photovoltaic device with a hot melt adhesive, such as EVA,

All references, including publications, patent applications, and patents, cited herein are hereby incorporated by reference to the same extent as if each reference were individually and specifically indicated to be

incorporated by reference and were set forth in its entirety herein.

The use of the terms "a" and "an" and "the" and similar referents in the context of describing the invention (especially in the context of the following claims) are to be construed to cover both the singular and the plural, unless otherwise indicated herein or clearly contradicted by context. The terms "comprising," "having," "including," and "containing" are to be construed as open-ended terms (i.e., meaning "including, but not limited to,") unless otherwise noted. Recitation of ranges of values herein are merely intended to serve as a shorthand method of referring individually to each separate value falling within the range, unless otherwise indicated herein, and each separate value is incorporated into the specification as if it were individually recited herein. All methods described herein can be performed in any suitable order unless otherwise indicated herein or otherwise clearly contradicted by context. The use of any and all examples, or exemplary language (e.g., "such as") provided herein, is intended merely to better illuminate the invention and does not pose a limitation on the scope of the invention unless otherwise claimed. No language in the specification should be construed as indicating any non- claimed element as essential to the practice of the invention.

Preferred embodiments of this invention are described herein, including the best mode known to the inventors for carrying out the invention. Variations of those preferred embodiments may become apparent to those of ordinary skill in the art upon reading the foregoing description. The inventors expect skilled artisans to employ such variations as appropriate, and the inventors intend for the invention to be practiced otherwise than as specifically described herein. Accordingly, this invention includes all modifications and equivalents of the subject matter recited in the claims appended hereto as permitted by applicable law. While certain optional features are described as embodiments of the invention, the description is meant to encompass and specifically disclose all combinations of these features unless specifically indicated otherwise or physically impossible.

Claims

A method of forming a photovoltaic device comprising the steps of: fixing components of the photovoltaic device together, said components comprising a front cover and a back cover, and forming a texture on the front cover or the back cover by bringing a material, said material being polymeric or polymerizable, on the front cover or the back cover in contact with a durable mould, wherein the steps of fixing components of the photovoltaic device together and forming a texture on a surface of the photovoltaic device are performed simultaneously.

The method of claim 1 , wherein the durable mould comprises a metal surface and wherein the step of forming a texture comprises bringing the material on the front cover or back cover in contact with the metal surface of the durable mould.

The method of claim 1 or 2, wherein the durable mould comprises a negative image of the texture.

The method of any one of claims 1 -3 further comprising the steps of reducing the viscosity of the material by heating the material, and increasing the viscosity of the material to a level sufficient to allow the material to retain a texture and to separate from the mould.

The method of any one of claims 1 to 4 further comprising the step of applying a pressure of from 0.05 to 0.2 MPa.

The method of any one of claims 1 to 5 wherein the components of the photovoltaic device further comprises an encapsulent.

The method of any one of claims 1 to 6 wherein the durable mould has recesses of from 1 micron to 1 millimeter in depth.

The method of any one of claims 1 to 7 wherein the durable mould has recesses of from 10 microns to 100 microns in depth.

The method of any one of claims 1 to 8 wherein the durable mould has a mean slope of at least 35°.

The method of any one of claims 1 to 9 wherein the formed texture has a mean slope of at least 35°. The method of any one of claims 1 to 10, wherein the texture depth retention ratio is greater than 90%.

The method of any one of claims 1 to 1 1 , wherein the texture depth retention ratio is 90% or greater and the mean slope of the formed texture is 35° or greater.

The method of any one of claims 1 to 12, wherein the texture depth retention ratio is 95% or greater and the mean slope of the formed texture is 40° or greater.

The method of any one of claims 1 to 14 wherein the material is a thermoplastic polymer.

The method of any one of claims 1 to 15 wherein the material is a semi- crystalline thermoplastic polymer.

The method of any one of claims 4-15 wherein the steps of reducing the viscosity and increasing the viscosity are effectuated by crossing either a glass transition temperature or a melting temperature transition of the material.

The method of any one of claims 4 through 16 wherein the viscosity is reduced to 2.5x10⁶ Pa s or less for at least 300 seconds.

The method of any one of claims 1 to 13, 16 or 17 wherein the material is polymerizable and is a sheet of polymerizable material comprising at least one initiator.

A method to apply a texture to a photovoltaic device which comprises a laminating step during which the front and back cover of said

photovoltaic devices are laminated together characterized in that while the laminating step is carried out a relief texture is imprinted onto or into one of the surfaces of the photovoltaic devices by a durable mould, which durable mould contains a relief texture and is placed inside the laminator, with the relief texture facing the surface that needs to be textured, wherein the front cover comprises a thermoplastic polymer. A laminator suitable for laminating a front and back cover of a photovoltaic device together, characterized in that the laminator comprises a durable mould, which durable mould contains a relief texture and is placed inside the laminator, with the relief texture facing the surface of the photovoltaic device that needs to be textured.