WO2021165792A1

WO2021165792A1 - Light redirecting film and photovoltaic module

Info

Publication number: WO2021165792A1
Application number: PCT/IB2021/051099
Authority: WO
Inventors: Vivian W. Jones; Jiaying Ma; Mark J. VOTAVA; Eric J. Iverson
Original assignee: 3M Innovative Properties Company
Priority date: 2020-02-21
Filing date: 2021-02-10
Publication date: 2021-08-26

Abstract

A flexible light redirecting film includes a continuous removable layer and a discontinuous light redirecting layer disposed on the removable layer and including a plurality of distinct spaced apart light redirecting portions extending along a first direction and arranged along an orthogonal second direction. Each light redirecting portion includes a structured polymeric portion having a first major surface facing the removable layer and an opposing structured second major surface including a plurality of linear microstructures; a structured adhesive portion including a structured third major surface facing, and substantially conforming to, the structured second major surface; and an optically reflective portion disposed between, and substantially conforming to, the structured second and third major surfaces. The light redirecting portions can be removed one at a time from the removable layer. A photovoltaic module and a method of applying a light redirecting film to a tabbing ribbon of a photovoltaic module are described.

Description

LIGHT REDIRECTING FILM AND PHOTOVOLTAIC MODULE

Background

Photovoltaic cells can be arranged in a row and electrically connected in series using tabbing ribbons. Light redirecting films can be applied over the tabbing ribbons.

Summary

In some aspects of the present disclosure, a flexible light redirecting film is provided. The light redirecting film includes a continuous first removable layer and a discontinuous light redirecting layer disposed on the first removable layer and including a plurality of distinct spaced apart substantially parallel light redirecting portions extending along a first direction and arranged along an orthogonal second direction. Each light redirecting portion includes a structured polymeric portion including a first major surface facing the continuous first removable layer and an opposing structured second major surface including a plurality of substantially parallel linear microstructures extending along a third direction and arranged along an orthogonal fourth direction; a structured adhesive portion including a structured third major surface facing, and substantially conforming to, the structured second major surface, and a fourth major surface opposite the structured third major surface; and an optically reflective portion disposed between, and substantially conforming to, the structured second and third major surfaces. The structured polymeric portion, the structured adhesive portion, and the optically reflective portion are substantially coextensive with each other. The light redirecting portions can be removed one at a time from the continuous first removable layer.

In some aspects of the present disclosure, a flexible light redirecting film is provided. The light redirecting film includes a flexible support layer and a plurality of distinct spaced apart substantially parallel light redirecting portions removably adhered to a same major surface of the support layer. The light redirecting portions extend along a first direction and are arranged along an orthogonal second direction. Each light redirecting portion includes a reflective layer including opposing structured first and second major surfaces in substantial conforming registration with each other where each of the structured first and second major surfaces includes a plurality of substantially parallel microstructures extending along a third direction and arranged along an orthogonal fourth direction and where the structured first major surface is disposed between the support layer and the structured second major surface; a polymeric layer disposed on and substantially planarizing the first major surface of the reflective layer to define a substantially planar first major surface of the polymeric layer facing the support layer; and an adhesive layer disposed on and substantially planarizing the second major surface of the reflective layer to define a substantially planar first major surface of the adhesive layer facing away from the support layer. The light redirecting portions can be removed one at a time from the support layer.

In some aspects of the present disclosure, a method of applying a light redirecting film to a tabbing ribbon of a photovoltaic module is provided. The method includes providing a photovoltaic module including a plurality of photovoltaic cells electrically connected by a plurality of substantially parallel tabbing ribbons extending along a first direction and arranged along an orthogonal second direction; providing an optical film including a removable carrier, and a plurality of individual spaced apart substantially parallel light redirecting films removably disposed on a same major surface of the removable carrier where the light redirecting films extend along a third direction and are arranged on the removable carrier along an orthogonal fourth direction and where each light redirecting film includes an adhesive layer disposed on a structured reflective layer away from the removable carrier; orienting the optical film so that the third direction is substantially parallel to the first direction and the adhesive layer of at least one of the light redirecting films faces, extends along substantially an entire length of, and is in substantial alignment and registration with, a corresponding at least one tabbing ribbon; and applying the adhesive layer of the at least one of the light redirecting films to the corresponding at least one tabbing ribbon, thereby transferring the at least one of the light redirecting films from the removable carrier onto the corresponding at least one tabbing ribbon.

In some aspects of the present disclosure, a photovoltaic module is provided. The photovoltaic module includes a plurality of photovoltaic cells connected by a plurality of substantially parallel tabbing ribbons extending along a first direction and arranged along an orthogonal second direction at a pitch P 1. For at least a majority of the tabbing ribbons, a first light redirecting film is disposed on the tabbing ribbon where the first light redirecting film extends along a length direction of the tabbing ribbon and has a substantially planar first major surface facing the tabbing ribbon and an opposite substantially planar second major surface having an average width W1 along a width direction orthogonal to the length direction. The light redirecting film includes an adhesive layer including the first major surface and an opposite structured third major surface where the structured third major surface includes a plurality of substantially parallel microstructures extending along a first direction and arranged along an orthogonal second direction and where the adhesive layer bonds the light redirecting film to the tabbing ribbon; a polymeric layer including the second major surface and an opposite fourth major surface facing, and substantially conforming to, the structured third major surface; and a reflective layer disposed between, and substantially coextensive with, the structured third and fourth major surfaces. For an integer N1 greater than 1, |P1/W1 - N 11 is less than 0.1.

These and other aspects will be apparent from the following detailed description. In no event, however, should this brief summary be construed to limit the claimable subject matter.

Brief Description of the Drawings

FIG. 1 is a schematic cross-sectional view of an illustrative light redirecting fdm according to some embodiments.

FIG. 2 schematic bottom plan view of an illustrative light redirecting fdm according to some embodiments.

FIG. 3 is a cross-sectional view of an illustrative light redirecting fdm which can be kiss- cut to define gaps between light redirecting portions.

FIG. 4 is a schematic cross-sectional view of another illustrative light redirecting fdm according to some embodiments.

FIG. 5 is a schematic cross-sectional view of an illustrative roll of optical fdm according to some embodiments.

FIGS. 6A-6B are schematic illustrations of an illustrative method of applying light redirecting film(s) to tabbing ribbon(s) of a photovoltaic module according to some embodiments.

FIG. 7 is a schematic top view of an illustrative photovoltaic module according to some embodiments.

FIGS. 8-10 are schematic cross-sectional views of an illustrative photovoltaic module according to some embodiments.

FIG. 11 is a schematic cross-sectional view of an illustrative single light redirecting fdm.

FIG. 12 is a schematic cross-sectional view of an illustrative reflective layer.

Detailed Description

In the following description, reference is made to the accompanying drawings that form a part hereof and in which various embodiments are shown by way of illustration. The drawings are not necessarily to scale. It is to be understood that other embodiments are contemplated and may be made without departing from the scope or spirit of the present description. The following detailed description, therefore, is not to be taken in a limiting sense.

Light redirecting films (LRFs), such as those described in U.S. Pat. No. 9,972,734 (Chen et ah), can be laminated onto the conducting tabbing ribbons (e.g., zinc plated copper tabbing ribbons) of (e.g., silicon) photovoltaic cells (e.g., solar cells), for example. The fdm can redirect/reflect light rays that would otherwise be absorbed or scattered by the tabbing ribbons to increase the captured power of the cell (e.g., by about 2%). Such films have typically included aluminum coated, 120 degree microreplicated prisms formed on a polyethylene terephthalate (PET) substrate with an adhesive on the PET substrate opposite the prisms for attaching the film to the tabbing ribbons.

The light redirecting films are typically provided in a roll and strips of the light redirecting film are cut from the roll in a slitting process and then laminated to the tabbing ribbons. This process typically accounts for a substantial portion of the cost of the LRF. According to some embodiments of the present disclosure, more cost effective methods of processing LRFs and assembling the LRFs to photovoltaic modules are provided. According to some embodiments of the present disclosure, an optical film includes a plurality of LRFs releasably attached to a carrier layer. In some embodiments, a light redirecting film is formed that includes a light redirecting layer and a removable carrier layer, or a removable carrier layer (e.g., a premask) can be subsequently added to a light redirecting layer that was formed separately. A kiss-cutting process (e.g., using a rotary die cutter) can then be utilized to cut strips, or light redirecting portions, from the light redirecting layer while only partially cutting into the carrier layer so that the strips remain removably attached to the carrier layer. A section of the light redirecting film having a width corresponding to a width of a photovoltaic module and having a length typically substantially larger than the width can be removed from the light redirecting film (before or after the kiss cutting process) and optionally wound onto a roll for further processing. The light redirecting film can then be applied to a photovoltaic module by aligning the light redirecting film relative to tabbing ribbons, for example, of the photovoltaic module and applying an appropriate pressure and/or heat to at least one of the strips to adhere the strip to the tabbing ribbon. Once the strip is adhered to the tabbing ribbon, the carrier layer can be removed from the strip. In some embodiments, the spacing between tabbing ribbons is an integer number times the width of the strips so that multiple strips can be applied to multiple tabbing ribbons in one step. The light redirecting film can then be shifted over so that another set of strips can be applied to another set of tabbing ribbons. Additional strips of LRFs can optionally be applied at other locations in the photovoltaic module as described further elsewhere.

Furthermore, traditional processing of LRFs into strips and applying the strips to tabbing ribbons becomes more difficult as the LRFs become thinner. One of the downsides with traditional LRF film is that it exacerbates the problem of cell fracture/cracking upon thermal cycling since the presence of tabbing ribbons can cause stress on the photovoltaic cell and the LRF disposed on the tabbing ribbons can increase the stress. This problem can be addressed by increasing the thickness of the encapsulating material (typically ethylene-vinyl acetate) to counteract the stress. Attaching the LRF to the tabbing ribbons may further increase the stress, and so the thickness of the encapsulating material would need to be further increased to counteract the stress. The need to increase the thickness of the encapsulating material is a problem for traditional LRFs since the industry is driving towards thinner and thinner solar cells to minimize material costs. According to some embodiments, the LRFs described herein are thin (e.g., less than about 55 micrometers thick, not including any carrier layer or release layer that may be present). The thin LRF can include an adhesive layer (e.g., a hot melt adhesive layer) disposed on a polymeric layer with an optically reflective (e.g., metal) layer disposed therebetween.

FIG. 1 is a schematic cross-sectional view of an illustrative light redirecting fdm 200 according to some embodiment of the present disclosure. The light redirecting fdm 200 can be flexible (e.g., sufficiently flexible that the film can be bend around a cylindrical mandrel having a radius of 2 cm). The light redirecting film 200 includes a continuous first removable layer 10 and a discontinuous light redirecting layer 20 disposed on the first removable layer 10. The discontinuous light redirecting layer 20 includes a plurality of distinct spaced apart substantially parallel (e.g., within 20 degrees or within 10 degrees or within 5 degrees of parallel) light redirecting portions 30 extending along a first direction (y-direction) and arranged along an orthogonal second direction (x-direction). Each light redirecting portion 30 includes a structured polymeric portion 40 including a first major surface 41 facing the continuous first removable layer 10 and an opposing structured second major surface 42 that includes a plurality of substantially parallel (e.g., linear) microstructures 50 extending along a third direction (y’ -direction; see, e.g., FIG. 2) and arranged along an orthogonal fourth direction (x’ -direction; see, e.g., FIG. 2). Each light redirecting portion 30 further includes a structured adhesive portion 80 including a structured third major surface 51 facing, and substantially conforming to, the structured second major surface, and a fourth major surface 52 opposite the structured third major surface; and an optically reflective portion 60 disposed between, and substantially conforming to, the structured second and third major surfaces 42 and 51. Substantially conforming surfaces can be nominally conforming, or conforming up to variations on a length scale smaller than or small compared to an average thickness of the layer 60, or conforming up to variations on a length scale small compared to an average peak to valley height h (see, e.g., FIG. 3) of the microstructures 50, for example. The structured polymeric portion 40, the structured adhesive portion 80, and the optically reflective portion 60 are substantially coextensive with each other. The light redirecting portions 30 can be removed one at a time from the continuous first removable layer 10.

The microstructures 50 can be linear prisms, for example. As another example, the microstructures 50 can extend primarily along a first axis but can have a lateral displacement from the first axis that can vary along the length of the microstructures such that the microstructures have a “wavy” shape as described in U.S. Pat. Appl. Pub. No. 2018/0040757 (O’Neill et ah), for example. Such “wavy” microstructures can be described as extending along a first direction and can be arranged along an orthogonal second direction such that the microstructures are substantially parallel. A microstructure can have at least two orthogonal dimensions (e.g., a height h (see, e.g., FIG. 3) and a width W2) that are each greater than about 10 nm and less than about 1 mm. At least some (e.g., at least a majority) of the microstructures 50 can have a length LI (see, e.g., FIG. 2) along a length direction (y’ direction of FIG. 2) greater than about 0.5 mm or greater than about 1 mm, for example.

In some embodiments, the first major surface 41 of the structured polymeric portion 40 of each light redirecting portion 30 is substantially planar. In some embodiments, the fourth major surface 52 of the structured adhesive portion 80 of each light redirecting portion 30 is substantially planar. A surface can be described as substantially planar if the surface is planar, or nominally planar (planar up to minor surface variations that would occur in normal manufacturing processes, for example), or planar up to minor surface variations (e.g., surface roughness) that are small or negligible compared to those provided by the structures of the opposing structured major surface.

The first removable layer 10 can be a carrier layer and/or a flexible support layer coextruded with the polymeric portion 40, for example. In some embodiments, the continuous first removable layer 10 has a substantially planar major surface 11 facing the discontinuous light redirecting layer 20. The removable layer 10 can also have a substantially planar major surface 13 opposite the major surface 11. In some embodiments, the continuous first removable layer 10 includes a plurality of spaced apart slits 12 extending along the first direction (y-direction) and arranged along the second direction (x-direction), where each slit 12 extends partially through a thickness t of the first removable layer 10. The slits 12 may also be referred to as score lines.

The light redirecting film 200 can further include an optional second removable layer 70 disposed on the structured adhesive portion 80 opposite the continuous first removable layer 10. The second removable layer 70 can be a release liner, for example. In some embodiments, the adhesive portion 80 is formed from a hot melt adhesive, for example, and the optional second removable layer 70 is omitted. In some embodiments, one or both of the major surfaces 13 and 52 is roughened to minimize points of contact with an adjacent layer when the light redirecting film 200 is rolled into a roll.

FIG. 2 schematic bottom plan view of an illustrative light redirecting film 200 according to some embodiments. The light redirecting film 200 includes a plurality of substantially parallel (e.g., linear) microstructures 50 extending along a third direction (y’-direction) and arranged along an orthogonal fourth direction (x’ -direction). In some embodiments, the third direction (y’- direction) makes an oblique angle a with the second direction (x-direction). In other embodiments, the third direction (y’ -direction) may be substantially parallel or substantially perpendicular to the second direction (x-direction).

In some embodiments, a flexible light redirecting fdm 200 includes a flexible support layer 10 and a plurality of distinct spaced apart substantially parallel light redirecting portions 30 removably adhered to a same major surface 11 of the support layer 10. The light redirecting portions extend along a first direction (y-direction) and are arranged along an orthogonal second direction (x-direction). Each light redirecting portion 30 includes a reflective layer 60 including opposing structured first (62) and second (61) major surfaces in substantial conforming registration with each other (e.g., nominally in conforming registration with each other, or in conforming registration with each other up to variations on a length scale smaller than or small compared to an average thickness of the layer 60, or in conforming registration with each other up to variations on a length scale small compared to an average peak to valley height h (see, e.g., FIG. 3) of the microstructures 50). Each of the structured first and second major surfaces 62 and 61 includes a plurality of substantially parallel (e.g., linear) microstructures 50 extending along a third direction (y’ -direction) and arranged along an orthogonal fourth direction (x’ -direction). The structured first major surface 62 is disposed between the support layer 10 and the structured second major surface 61. Each light redirecting portion 30 further includes a polymeric layer 40 disposed on and substantially planarizing the first major surface 62 of the reflective layer 60 to define a substantially planar first major surface 41 of the polymeric layer 40 facing the support layer 10. Each light redirecting portion 30 further includes an adhesive layer 80 disposed on and substantially planarizing the second major surface 61 of the reflective layer 60 to define a substantially planar first major surface 52 of the adhesive layer facing away from the support layer 10. The light redirecting portions 30 can be removed one at a time from the support layer 10. The polymeric layer 40 has a second major surface 42 of the polymeric layer 40 that may substantially conform to the first major surface 62 of the reflective layer 60. The adhesive layer 80 has a second major surface 51 of the adhesive layer 80 that may substantially conform to the second major surface 61 of the reflective layer 60.

In some embodiments, each pair of adjacent light redirecting portions 30 defines a substantially v-shaped gap 31 therebetween. The gaps 31 can be formed by a kiss-cutting process, for example, where the cut extends only partially into the support layer 10. In some embodiments, the flexible support layer 10 includes a plurality of spaced apart slits 12, also referred to as score lines, extending along the first direction (y-direction) and arranged along the second direction (x- direction), where each slit 12 extends partially through a thickness t of the flexible support layer 10. The slits 12 extends only partially through the thickness t of the flexible support layer 10 so that the flexible support layer 10 remains a continuous layer. In some embodiments, the kiss- cutting process is carried out using a rotary die cutter. The rotary die cutter can be oriented such that the blades make a small angle (e.g., about a half of a degree) with the web direction.

FIG. 3 is a cross-sectional view of an illustrative light redirecting fdm 201 which can be kiss-cut to define gaps 31 (see, e.g., FIG. 1) between light redirecting portions 30 (see, e.g., FIG.

1). In some embodiments, the layers 10 and 40 formed together by coextrusion, layer 60 is then deposited on the structured surface 42 (e.g., layer 60 can be an aluminum or other metal layer deposited by sputtering or evaporative deposition), layer 80 is then deposited onto layer 60. For example, layer 80 can be extruded onto layer 60 at a temperature above the softening temperature of the layer 80 and cast against a chill roll, which can have a flat or roughened surface. As another example, layer 80 can be formed by laminating a film adhesive to the surface of layer 60 by thermally embossing the film at a nip using layer 60 to form structures in the film (e.g., using layer 60 as an "embossing roll”). A surface treatment (e.g., oxygen plasma treatment) can be applied to the structured surface 61 of the layer 60 prior to depositing the layer 80 to improve adhesion. After the layers 60 and 80 are formed, one or both of the layers may be cross-linked (e.g., via electron- beam cross-linking) to provide improved mechanical stability, for example. Other light redirecting films similar to light redirecting film 201 that can be used in the present disclosure are described in U.S. Pat. Appl. No. 62/950261 filed on December 19, 2019 and titled “Light Redirecting Film”.

Alternatively, instead of forming the polymeric layer 40 with the first removable layer 10, the polymeric layer 40 can be formed separately, and the reflective layer 60 can then be deposited. FIG. 4 is a schematic cross-sectional view of an illustrative flexible light redirecting film 300. A first removable layer 10 and be releasably attached to the reflective layer 60, and an adhesive layer 80 can be applied to the polymeric layer 40 opposite the reflective layer 60, and an optional second removable layer 70 can be disposed on the adhesive layer 80 opposite the first removable layer 10. The layers can be cut through (e.g., using a plurality of blades and/or a plurality of cutting steps) from the second removable layer 70 to the first removable layer 10. The cut can partially penetrate into the first removable layer 10 to form a plurality of spaced apart slits 12 extending along the first direction (y-direction) and arranged along the second direction (x-direction). The first removable layer 10 can be a protective premask layer which can be tacky for bonding to the reflective layer 60. The second removable layer 70 can be a release liner.

In some embodiments, the light redirecting film 200 or 300, for example, is provided as a roll of the film.

FIG. 5 is a schematic cross-sectional view of a roll 400 of optical film 500. The optical film 500 can correspond to light redirecting film 200 or 300, for example. The optical film 500 is rolled along a length direction (x-direction) orthogonal to a width direction (y-direction) of the optical film 500 to form a roll 400 of the optical film 500. The optical film 500 has a length L and a width W along the respective length and width directions, where L/W > 10. In some embodiments, L/W > 30 or L/W > 100. The optical fdm 500 includes a continuous removable carrier 10 substantially coextensive with the optical fdm 500 in length and width; and a plurality distinct spaced apart substantially parallel light redirecting fdms 30 removably adhered to a same major surface 11 of the removable carrier 10. The light redirecting fdms extend along the width direction and are arranged along the length direction. Each light redirecting fdm includes a reflective layer 60 having a zig-zag shape defining a plurality of angled sides extending along a first direction (y’-direction) and arranged along an orthogonal second direction (x’ -direction). In some embodiments, the first direction (e.g., the y’-direction of FIG. 2) makes an oblique angle a with the length direction (e.g., the x-direction of FIG. 2). The optical fdm can be rolled with the continuous removable carrier 10 facing the inside or the outside of the roll 400.

In some embodiments, each light redirecting film 30 further includes a structured adhesive layer 80 having a structured major surface 51 facing, and substantially conforming to, the reflective layer. In some embodiments, each light redirecting fdm 30 further includes a structured polymeric layer 40, where the reflective layer 60 is disposed between the structured polymeric layer 40 and the adhesive layer 80 with the structured polymeric layer 40 having a structured major surface 42 facing, and substantially conforming to, the reflective layer 60.

Suitable materials for the layer 40 include thermoplastic olefin (TPO) polymers and copolymers (including, for example, linear low-density polyethylene (FFDPE) or high-density polyethylene (HDPE)), fluoropolymers (e.g., polyvinylidene fluoride (PVDF)) or fluoropolymer blends, cyclic olefin copolymers, or blends thereof, for example. Such polymers have refractive indices similar to encapsulants used in solar cell applications and are photochemically stable to wavelengths experienced in solar cell applications. Other suitable materials for layer 40 include polycarbonate, (co)polyester (polyester or copolyester), or combinations thereof, optionally blended with one or more other polymers or copolymers described elsewhere for layer 40 to lower the refractive index, for example. Suitable TPO resins include TPX Grade DX310, a 4- methylpentene-1 -based olefin copolymer (also known as polymethylpentene) available from Mitsui Chemicals America, Inc. (Rye Brook, NY 10573 USA), and HD6719, a high density polyethylene copolymer available from Exxon Mobil Chemical (Baytown, TX 77520 USA).

Reflective layer 60 can be a metal layer or a dielectric reflector, for example. In some embodiments, the reflective layer 60 is electrically conductive. In some embodiments, the reflective layer 60 is or incudes a metal layer. The metal layer can include one or more of silver, gold and aluminum. For example, the metal layer can be an aluminum layer. As an alternative to a metal layer, a dielectric reflector can be used as the reflective layer. Dielectric reflectors including alternating layers are known in the art. FIG. 12 is a schematic cross-sectional view of a portion of an illustrative reflective layer 60, according to some embodiments. In the illustrated embodiment, the reflective layer includes a plurality of alternating lower index first (101) and higher index second (102) layers. The refractive index of the first layers 101 is denoted nl and the refractive index of the second layers 102 is denoted n2. Refractive indices are determined at 532 nm, unless indicated otherwise. In some embodiments, n2-nl is at least about 0.05, or at least about 0.1. The alternating first and second layers can be deposited by vapor deposition or by any suitable thin- film deposition technique known in the art. One or both of the first and second layers can be inorganic or organic. In some embodiments, the lower index first layers 101 are organic polymeric layers and the higher index second layers 102 are inorganic layers. Substantially normally incident light 333 is schematically illustrated in FIG. 12.

In some embodiments, for substantially normally incident light (e.g., within 20 degrees or 10 degrees or 5 degrees of normally incident) and for at least one wavelength in a range from about 350 nm to about 1100 nm, the reflective layer 60 (e.g., metal layer or dielectric reflector) reflects at least 60%, or at least 70%, or at least 80% of the incident light. In some embodiments, for substantially normally incident light, the reflective layer 60 has an average reflectance of at least 60% in a wavelength range from about 450 nm to about 650 nm, or from about 350 nm to about 1100 nm.

Layer 10 can be formed from any polymer that provides a desired peel force with layer 40. For example, the material for layer 10 can be selected to be a polymer that is incompatible with the material of layer 40 so that the layer 10 can readily separate from the layer 40. In some embodiments, layer 10 is or includes polycarbonate or (co)polyester based resins. Suitable materials for layer 10 include MARKROLON 2407, a polycarbonate available from Covestro North America (Pittsburgh, PA 15205 USA), and EASTAR GN071 is a copolyester available from Eastman Chemical Company (Kingsport, TN 37660 USA).

Layer 70, if included, can be any suitable release liner such as a suitably coated polyester, polypropylene or polyethylene film, for example.

Layer 80 can be any suitable adhesive layer and can include one or more of a hot melt adhesive, a heat activated adhesive, a pressure sensitive adhesive, a structural adhesive, or an optically clear adhesive, for example. In some embodiments, layer 80 is a hot melt adhesive layer. Hot melt adhesives are thermoplastic materials that are typically solid and non-tacky at room temperature (e.g., 20 °C) but melt and flow upon heating. Hot melt adhesives are applied in the molten state and form a bond upon cooling to a solid state. Suitable hot melt adhesives include those that include ethylene-vinyl acetate (EVA) copolymer, polyolefin, metallocene polyolefin (e.g., metallocene polyethylene), polyamide, polyester, polyurethane, or styrene block copolymer, for example. These materials can be blended with tackifier(s). For example, an EVA-based hot melt adhesive can include EVA blended with terpene -phenol resin (TPR) tackifier. Suitable EVA- based hot melt adhesives are available from 3M Company, St. Paul, MN, or from Dow Chemical Company, Midland, MI, for example. Exemplary EVA-based hot melt adhesives include ELVAX 3180 and ELVAX 3175, both available from Dow Chemical Company. Suitable polyolefin-based adhesives include amorphous polyolefin hot melt adhesives, for example. Other suitable hot melt adhesives include copolymers of ethylene and methyl acrylate such as ELVALOY 1224 available from Dow Chemical Company. Still other suitable hot melt adhesives include ethylene acid copolymers such as those available under the tradename NUCREL from Dow Chemical Company.

FIGS. 6A-6B are schematic illustrations of an illustrative method of applying light redirecting film(s) 30 to tabbing ribbon(s) 91 of a photovoltaic module 90. FIG. 6A is a schematic cross-sectional view of a photovoltaic module 90 and a roll of optical film 500 that includes light redirecting films 30 as described elsewhere. FIG. 6B is a schematic top view of an illustrative photovoltaic module 90 and a roll of optical film 500 that includes light redirecting films 30 as described elsewhere. The photovoltaic module 90 can include other features not shown in FIGS. 6A-6B) (see, e.g., FIG. 7 described elsewhere). The method includes providing a photovoltaic module 90 including a plurality of photovoltaic cells 92 electrically connected by a plurality of substantially parallel tabbing ribbons 91 extending along a first direction (yl -direction) and arranged along an orthogonal second direction (xl -direction); and providing an optical film 500 including a removable carrier 10, and a plurality of individual spaced apart substantially parallel light redirecting films 30 removably disposed on a same major surface 11 of the removable carrier 10. The light redirecting films 30 extend along a third direction (y-direction) and are arranged on the removable carrier 10 along an orthogonal fourth direction (x-direction). Each light redirecting film 30 includes an adhesive layer 80 disposed on a structured reflective layer 60 away from the removable carrier. The method further includes orienting the optical film 500 so that the third direction (y-direction) is substantially parallel to the first direction (yl -direction) and the adhesive layer 80 of at least one of the light redirecting films 30 faces, extends along substantially an entire length (e.g., at least 60% or at least 70% or at least 80% or at least 90% of the length) of, and is in substantial alignment and registration with, at least one corresponding tabbing ribbon 91 (e.g., sufficiently aligned and registered such that the adhesive layer overlaps at least 60% or at least 70% or at least 80% or at least 90% or 100% of the width of the tabbing ribbon over substantially the entire length of the tabbing ribbon); and applying the adhesive layer 80 of the at least one of the light redirecting films 30 to the corresponding at least one tabbing ribbon 91, thereby transferring the at least one of the light redirecting films 30 from the removable carrier 10 onto the corresponding at least one tabbing ribbon 90. In some embodiments, the at least one of the light redirecting films includes a plurality of the light redirecting films. In such embodiments, the corresponding at least one tabbing ribbon can then include a plurality of tabbing ribbons. In some embodiments, applying the adhesive layer 80 of the at least one of the light redirecting fdms 30 to the corresponding at least one tabbing ribbon 91 includes using a tool 77 to apply pressure to the at least one of the light redirecting fdms 30. Heat may also be applied (e.g., when the adhesive layer 80 is a hot-melt adhesive layer). For example, photovoltaic cells 92 can be heated to a temperature in a range of 120 °C to 140 °C or 120 °C to 140 °C, for example. In some embodiments, the photovoltaic cells 92 are heated to a temperature above a softening temperature of the adhesive layer 80.

In some embodiments, the tabbing ribbons are spaced part by an integer number of widths of the light redirecting fdms 30 so that a plurality of the light redirecting fdms 30 can be transferred to the tabbing ribbons 91 and remain aligned and registered with the tabbing ribbons. In some embodiments, the tabbing ribbons 91 are arranged along the second direction (xl -direction) at a pitch PI, the at least one of the light redirecting fdms 30 have an average width W1 (see, e.g., FIG. 2), where for an integer N1 greater than 1, |P1/W1 - N 11 is less than 0.1. In some embodiments, N1 is in a range of 3 to 300, or 5 to 200, or 8 to 100. In some such embodiments, or in other embodiments, |P1/W1 - N 11 is less than 0.05, or 0.03, or 0.02, or 0.01.

FIG. 7 is a schematic top view of an illustrative photovoltaic module 90 according to some embodiments. FIGS. 8-10 are schematic cross-sectional views of an illustrative photovoltaic module 90 according to some embodiments. In FIG. 8, the cross-section is through and perpendicular to the length direction of the tabbing ribbons 91. In FIG. 9, the cross-section is between adjacent tabbing ribbons 91. In FIG. 10, the cross-section is along a tabbing ribbon 91. FIG. 11 is a schematic cross-sectional view of a light redirecting film 30 according to some embodiments. The light redirecting film 30 of FIG. 11 can be used as any of the light redirecting fdms of FIGS. 8-10. In FIG. 7, the tabbing ribbons 91 extend along the yl -direction referring to the indicated xl-yl-zl coordinate system. In FIGS. 8-10 the light redirecting fdms 30 extend along a y-direction referring to the indicated x-y-z coordinate system. The x-y-z directions of FIGS. 8-10 are considered to be aligned with the respective xl-yl-zl directions of FIG. 7 and so separate xl- yl-zl coordinates are not illustrated in FIGS. 8-10.

In some embodiments, a photovoltaic module 90 includes a plurality of photovoltaic cells 92 connected by a plurality of substantially parallel tabbing ribbons 91 extending along a first direction (yl -direction) and arranged along an orthogonal second direction (xl -direction) at a pitch PI (see, e.g., FIG. 6B). For at least a majority of the tabbing ribbons 91, a first light redirecting film 30 is disposed on the tabbing ribbon 91, where the first light redirecting film 30 extends along a length direction of the tabbing ribbon 91 and has a substantially planar first major surface 52 facing the tabbing ribbon and an opposite substantially planar second major surface 41. The second major surface 41 has an average width W1 along a width direction (x-direction) orthogonal to the length direction (y-direction). The first light redirecting film 30 has a thickness tl between the first and second major surfaces 52 and 41. The thickness tl can be less than about 65 micrometers, or less than about 60 micrometers, or less than about 55 micrometers, or less than about 50 micrometers, or less than about 45 micrometers, or less than about 40 micrometers. In some embodiments, the thickness tl is in a range of about 10 micrometers to about 55 micrometers, or about 15 micrometers to about 50 micrometers, or about 20 micrometers to about 45 micrometers, for example. The light redirecting film 30 includes an adhesive layer 80 including the first major surface 52 and an opposite structured third major surface 51, where the structured third major surface 51 includes a plurality of substantially parallel microstructures 50 extending along a first direction (y’ -direction) and arranged along an orthogonal second direction (x’- direction). The adhesive layer 80 bonds the light redirecting film 30 to the tabbing ribbon 19. The light redirecting film 30 further includes a polymeric layer 40 including the second major surface 41 and an opposite fourth major surface 42 facing, and substantially conforming to, the structured third major surface 51; and a reflective layer 60 disposed between, and substantially coextensive with, the structured third and fourth major surfaces 51 and 42. In some embodiments, for an integer N1 greaterthan 1, |P1/W1 - N 11 is less than 0.1. In some embodiments, N 1 is in a range of 3 to 300, or 5 to 200, or 8 to 100. In some such embodiments, or in other embodiments, |P1/W1 - N 11 is less than 0.05, or 0.03, or 0.02, or 0.01. In some embodiments, each tabbing ribbon 91 has an average width W2 in the width direction (x-direction), where W1 > W2. In some embodiments, W1 is at least 1.1 or 1.2 times W2.

Layers (resp., films, surfaces) can be described as substantially coextensive with each other if at least about 60% by area of one layer (resp., film, surface) is coextensive with at least about 60% by area of the other layer (resp., film, surface). In some embodiments, for layers (resp., films, surfaces) describes as substantially coextensive, at least about 80% or at least about 90% by area of one layer (resp., film, surface) is coextensive with at least about 80% or at least about 90% by area of the other layer (resp., film, surface). Layers (resp., films, surfaces) can be described as having substantially coextensive lengths or widths if at least about 60% of the length or width of one layer (resp., film, surface) is coextensive with at least about 60% of the respective length or width of the other layer (resp., film, surface). In some embodiments, for layers (resp., films, surfaces) describes as having substantially coextensive lengths or widths, at least about 80% or at least about 90% of the respective length or width of one layer (resp., film, surface) is coextensive with at least about 80% or at least about 90% of the respective length or width of the other layer (resp., film, surface). In some embodiments, the photovoltaic cells 92 are spaced apart in a layer 96 of the photovoltaic cells 92 defining gaps 95 between adjacent photovoltaic cells 92. In some embodiments, for each gap 95 in a plurality of the gaps 95, a second light redirecting film 32 is disposed adjacent the gap 95 such that in a top plan view, the second light redirecting film 32 extends along a length direction of the gap (y-direction) and overlaps a width of the gap. The second light redirecting film 32 includes a reflective first layer 60 disposed on, and substantially conforming to, a structured major surface of a second layer (e.g., one or both of layers 40 and 80). The second light redirecting film 32 can be as described for the light redirecting film 30 of FIG.

11, for example, or as described for the light redirecting film 30 of FIG. 4 after being removed from the layer 10 and optional layer 70 if included, for example. In some embodiments, the layer 96 of the photovoltaic cells 92 is disposed adjacent a backing layer 93, where the second light redirecting films 32 are disposed on the backing layer 93 facing the layer of photovoltaic cells 92. For example, the second light redirecting films 32 can be positioned on the backing layer 93 using a process similar to that illustrated in FIGS. 6A-6B. Then, an encapsulant layer can be disposed over the backing layer and second light redirecting films 32. Then, a layer of the photovoltaic cells 92 can be disposed on the encapsulant layer followed by applying the first light redirecting films 30 to the tabbing ribbons 91. Then, a second encapsulant layer and cover layer 99 can be disposed over the photovoltaic cells 92 and the light redirecting films 30. In some embodiments, the backing layer 93 is or includes a polymeric backsheet. In some embodiments, the backing layer 93 is or includes a glass layer. In some embodiments, the photovoltaic module 90 further includes a cover layer 99, where the layer 96 of the photovoltaic cells 92 is disposed between the cover and the backing layers 99 and 93. In some embodiments, the photovoltaic module 90 further includes an encapsulant 98 disposed between the cover and backing layers 99 and 93 and encapsulating the photovoltaic cells 92.

Examples

Structured films were made where a carrier layer was coextruded with a thermoplastic polyolefin resin using a die equipped with a multilayer feedblock. A cylindrically-shaped metal roll with finely detailed prismatic channels cut into its outer surface served as the mold. The two layers were coextruded such that the carrier layer contacted a rubber nip roll and the thermoplastic polyolefin resin contacted the cylindrically-shaped metal roll with finely detailed prismatic channels. Layers 10 and 40 of FIG. 3 (without the other layers of the figure) is representative of such a two-layered structured film. The thickness of layer 40 was approximately 22 micrometers and the thickness of the carrier layer 10 was approximately 75 micrometers. The material of the carrier layer was selected to be incompatible with the thermoplastic polyolefin resin such that the two layers could readily separate from each other when in film format. Two-layered structured films were made using TPX Grade DX3104-methylpentene-l- based olefin copolymer (available from Mitsui Chemicals America, Inc., Rye Brook, NY, USA) as the thermoplastic polyolefin resin and MAKROLON 2407 polycarbonate (available from Covestro North America, Pittsburgh, PA, USA) as the resin for the carrier layer. The structured surface of the TPX Grade DX310/MAKROUON 2407 film was treated using an oxygen plasma and then immediately (in the same vacuum chamber) coated with 60-100 nm of aluminum using a sputter coater.

The aluminum metal coated film was then coated with a hot melt adhesive (NUCREU ethylene acid copolymer, available from Dow Chemical Company, Midland, MI, USA) by extruding the adhesive above its softening point and casting the hot melt against a chilled roll to yield an approximately 25 micrometer thick layer. The total thickness of the sample not including the carrier layer (layer 10) was about 47 micrometers.

The resulting light redirecting film was then kiss-cut using a rotary die resulting in gaps 31 between adjacent light redirecting portions 30 (strips of light redirecting film) as generally illustrated in FIG. 1. The film, which was wound onto a roll of the film after being kiss-cut, was 6 inches wide and the light redirecting strips (portions 30) had a width of 1.2 mm.

The light redirecting strips were applied to the tabbing ribbons of a 156mm x 156mm 3- tabbing ribbon crystalline silicon solar cell using the process generally illustrated in FIGS. 6A-6B. The solar cell was heated from the bottom to a temperature of 130 - 140 °C. A pressure was applied to a light redirecting strip for 1-2 seconds to attach the light redirecting strip to a tabbing ribbon. The pressure, temperature and time were sufficient for the hot melt adhesive layer of the light redirecting strip to bond to the tabbing ribbon. The light redirecting strips were applied one at a time and the film was manually translated a fixed distance after applying a light redirecting strip to a tabbing ribbon to align another light redirecting strip to another tabbing ribbon.

Terms such as “about” will be understood in the context in which they are used and described in the present description by one of ordinary skill in the art. If the use of “about” as applied to quantities expressing feature sizes, amounts, and physical properties is not otherwise clear to one of ordinary skill in the art in the context in which it is used and described in the present description, “about” will be understood to mean within 10 percent of the specified value. A quantity given as about a specified value can be precisely the specified value. For example, if it is not otherwise clear to one of ordinary skill in the art in the context in which it is used and described in the present description, a quantity having a value of about 1, means that the quantity has a value between 0.9 and 1.1, and that the value could be 1.

All references, patents, and patent applications referenced in the foregoing are hereby incorporated herein by reference in their entirety in a consistent manner. In the event of inconsistencies or contradictions between portions of the incorporated references and this application, the information in the preceding description shall control.

Descriptions for elements in figures should be understood to apply equally to corresponding elements in other figures, unless indicated otherwise. Although specific embodiments have been illustrated and described herein, it will be appreciated by those of ordinary skill in the art that a variety of alternate and/or equivalent implementations can be substituted for the specific embodiments shown and described without departing from the scope of the present disclosure. This application is intended to cover any adaptations, or variations, or combinations of the specific embodiments discussed herein. Therefore, it is intended that this disclosure be limited only by the claims and the equivalents thereof.

Claims

What is claimed is:

1. A flexible light redirecting fdm comprising: a continuous first removable layer; a discontinuous light redirecting layer disposed on the first removable layer and comprising a plurality of distinct spaced apart substantially parallel light redirecting portions extending along a first direction and arranged along an orthogonal second direction, each light redirecting portion comprising: a structured polymeric portion comprising a first major surface facing the continuous first removable layer and an opposing structured second major surface comprising a plurality of substantially parallel linear microstructures extending along a third direction and arranged along an orthogonal fourth direction; a structured adhesive portion comprising a structured third major surface facing, and substantially conforming to, the structured second major surface, and a fourth major surface opposite the structured third major surface; and an optically reflective portion disposed between, and substantially conforming to, the structured second and third major surfaces, wherein the structured polymeric portion, the structured adhesive portion, and the optically reflective portion are substantially coextensive with each other, and wherein the light redirecting portions can be removed one at a time from the continuous first removable layer.

2. The flexible light redirecting film of claim 1, wherein each light redirecting portion further comprises a second removable layer disposed on the structured adhesive portion opposite the continuous first removable layer.

3. The flexible light redirecting film of claim 1 or 2, wherein the continuous first removable layer comprises a substantially planar major surface facing the discontinuous light redirecting layer.

4. The flexible light redirecting film of any one of claims 1 to 3, wherein the first major surface of the structured polymeric portion of each light redirecting portion is substantially planar.

5. The flexible light redirecting film of any one of claims 1 to 4, wherein the fourth major surface of the structured adhesive portion of each light redirecting portion is substantially planar.

6. A flexible light redirecting film comprising: a flexible support layer; a plurality of distinct spaced apart substantially parallel light redirecting portions removably adhered to a same major surface of the support layer, the light redirecting portions extending along a first direction and arranged along an orthogonal second direction, each light redirecting portion comprising: a reflective layer comprising opposing structured first and second major surfaces in substantial conforming registration with each other, each of the structured first and second major surfaces comprising a plurality of substantially parallel microstructures extending along a third direction and arranged along an orthogonal fourth direction, the structured first major surface disposed between the support layer and the structured second major surface; a polymeric layer disposed on and substantially planarizing the first major surface of the reflective layer to define a substantially planar first major surface of the polymeric layer facing the support layer; and an adhesive layer disposed on and substantially planarizing the second major surface of the reflective layer to define a substantially planar first major surface of the adhesive layer facing away from the support layer, wherein the light redirecting portions can be removed one at a time from the support layer.

7. The flexible light redirecting film of claim 6, wherein flexible support layer comprises a plurality of spaced apart slits extending along the first direction and arranged along the second direction, each slit extending partially through a thickness of the flexible support layer.

8. A roll of optical film rolled along a length, orthogonal to a width, direction of the optical film to form a roll of the optical film, the optical film comprising: a length L and a width W along the respective length and width directions, L/W > 10; a continuous removable carrier substantially coextensive with the optical film in length and width; and a plurality distinct spaced apart substantially parallel light redirecting films removably adhered to a same major surface of the removable carrier, the light redirecting films extending along the width direction and arranged along the length direction, each light redirecting film comprising a reflective layer having a zig-zag shape defining a plurality of angled sides extending along a first direction and arranged along an orthogonal second direction.

9. The roll of claim 8, wherein each light redirecting film further comprises a structured adhesive layer comprising a structured major surface facing, and substantially conforming to, the reflective layer.

10. The roll of claim 9, wherein each light redirecting film further comprises a structured polymeric layer, the reflective layer disposed between the structured polymeric layer and the adhesive layer, the structured polymeric layer comprising a structured major surface facing, and substantially conforming to, the reflective layer.

11. A method of applying a light redirecting film to a tabbing ribbon of a photovoltaic module, the method comprising: providing a photovoltaic module comprising a plurality of photovoltaic cells electrically connected by a plurality of substantially parallel tabbing ribbons extending along a first direction and arranged along an orthogonal second direction; providing an optical film comprising a removable carrier, and a plurality of individual spaced apart substantially parallel light redirecting films removably disposed on a same major surface of the removable carrier, the light redirecting films extending along a third direction and arranged on the removable carrier along an orthogonal fourth direction, each light redirecting film comprising an adhesive layer disposed on a structured reflective layer away from the removable carrier; orienting the optical film so that the third direction is substantially parallel to the first direction and the adhesive layer of at least one of the light redirecting films faces, extends along substantially an entire length of, and is in substantial alignment and registration with, a corresponding at least one tabbing ribbon; and applying the adhesive layer of the at least one of the light redirecting films to the corresponding at least one tabbing ribbon, thereby transferring the at least one of the light redirecting films from the removable carrier onto the corresponding at least one tabbing ribbon.

12. The method of claim 11, wherein the at least one of the light redirecting films comprises a plurality of the light redirecting films.

13. The method of claim 11 or 12, wherein the tabbing ribbons are arranged along the second direction at a pitch PI, the at least one of the light redirecting films having an average width Wl, wherein for an integer N1 greater than 1, |P1/W1 - N 11 is less than 0.1.

14. A photovoltaic module comprising a plurality of photovoltaic cells connected by a plurality of substantially parallel tabbing ribbons extending along a first direction and arranged along an orthogonal second direction at a pitch PI, wherein for at least a majority of the tabbing ribbons, a first light redirecting film is disposed on the tabbing ribbon, the first light redirecting film extending along a length direction of the tabbing ribbon and having a substantially planar first major surface facing the tabbing ribbon and an opposite substantially planar second major surface, the second major surface having an average width W1 along a width direction orthogonal to the length direction, the light redirecting film comprising: an adhesive layer comprising the first major surface and an opposite structured third major surface, the structured third major surface comprising a plurality of substantially parallel microstructures extending along a first direction and arranged along an orthogonal second direction, the adhesive layer bonding the light redirecting film to the tabbing ribbon; a polymeric layer comprising the second major surface and an opposite fourth major surface facing, and substantially conforming to, the structured third major surface; and a reflective layer disposed between, and substantially coextensive with, the structured third and fourth major surfaces, wherein for an integer N1 greater than 1, |P1/W1 - N 11 is less than 0.1.

15. The photovoltaic module of claim 14, wherein |P1/W1 - N 11 is less than 0.05.