BACKGROUND

Field

[0001] The present disclosure generally relates to transparent composites which are useful for improving indoor illumination.

Description of the Related Art

[0002] With the recent increase in environment and energy-related issues, the needs for energy-saving industrial products has drawn a significant amount of interest in recent years. One approach being considered to reduce energy consumption in buildings is the more efficient use of sunlight to provide lighting inside buildings.

SUMMARY

[0003] Described herein are transparent composites which are useful for improving indoor illumination. The transparent composite redirects sunlight so that illumination inside the building is improved while also reducing or eliminating glaring. In some embodiments, the sunlight redirecting transparent composite comprises a transparent substrate and a holographic element, wherein the holographic element comprises an interference pattern that diffracts a selected portion of the incident solar light such that the light is redirected into the building at angle that provides improved illumination within the building. In some embodiments, the diffractive structures are the same throughout the area of the holographic element. In some embodiments, the diffractive structures continuously vary across the area defined by a surface of the holographic element, such as a surface that overlays or contacts the transparent substrate. In some embodiments, the system may also comprise luminescent wavelength conversion elements. In some embodiments, the luminescent material absorbs UV photons and converts these photons into visible wavelengths. In some embodiments, the system may also comprise UV absorbing elements.

[0004] In some embodiments, the diffractive structures are the same across the surface of the holographic element. In some embodiments, the diffractive structures continuously vary across the surface of the holographic element. In some embodiments, the holographic element is configured with multiple diffractive structures. In some embodiments, the diffractive structures of the holographic element vary throughout the area defined by the surface of the holographic element, such that light incident on one side of the holographic element is diffracted at a different angle than the light incident on a different side of the holographic element. In some embodiments, the diffractive structures of the holographic element are continuously varying throughout the area defined by the surface of the holographic element.

[0005] In some embodiments, the holographic element is configured to diffract incident light of greater than 80 degrees, greater than 60 degrees, greater than 30 degrees, or greater than 5 degrees, greater than 80 degrees or less than -80 degrees, greater than 60 degrees or less than -60 degrees, greater than 30 degrees or less than -30 degrees, or greater than 5 degrees or less than -5 degrees (from horizontal, or from a direction normal to the face of the window) at an angle that redirects these photons into the building such that the illumination is improved.

[0006] In some embodiments, the holographic element is configured to diffract photons at a different angle depending on the incident wavelength.

[0007] The transparent composite may be configured to be transparent at a variety of viewing angles depending on the application and/or location of the window in the building or vehicle, and/or the longitudinal location of the building. In some embodiments of the transparent composite, the transparent composite is transparent for a viewing angle of 0 degrees (i.e., the transparent composite is transparent when looking straight through the window, see FIG. 1). In some embodiments of the transparent composite, the transparent composite is transparent for a viewing angle of about +20 degrees to about -20 degrees, about +40 degrees to about -40 degrees, about +60 degrees to about -60 degrees, about +90 degrees to about -90 degrees, about +20 degrees to about -90 degrees, about +40 degrees to about -90 degrees from horizontal, or from normal to the face of the window.

[0008] In order for the transparent composite to be applicable to window based applications, the transparent composite may be transparent to provide undistorted viewing of the scenery through the window. The transmittance of visible light (wavelengths of light between about 400 nm and about 700 nm) through the transparent composite is a good indicator of transparency. In some embodiments of the transparent composite, the transparent composite has a transmittance in at least one viewing angle of at least 50%, at least 60%, at least 70%, at least 80%, or at least 90% for wavelengths of light between about 400 nm and about 700 nm. [0009] In some embodiments, the window may be placed vertically in a building. In some embodiments, the holographic element is configured to diffract light incident on the system at angles of greater than about +70 degrees, about +50 degrees, about +30 degrees, about +15 degrees from the horizontal, or from the direction normal to the face of the window.

[0010] In some embodiments, the window may be placed horizontally (such as a sky light in a building or vehicle), in which case the holographic element(s) may be configured based on the desired viewing angle and/or the optimal light redirection illumination needed for the particular room.

[0011] In some embodiments, a luminescent material is incorporated into the transparent composite to further enhance the illumination effect. In some embodiments, the luminescent material absorbs UV photons and converts these photons into visible wavelengths.

[0012] In some embodiments of the transparent composite, the transparent substrate further comprises a luminescent material, wherein said luminescent material acts to absorb incident photons of a particular wavelength range, and re-emit those photons at a different wavelength. In some embodiments, the re-emitted photons are internally reflected and refracted within the transparent substrate until they reach the edge surfaces where they can escape. In some embodiments, the re-emitted photons are directed into the building to further provide improved illumination. In some embodiments, the luminescent material absorbs photons of UV wavelengths and converts them into visible wavelengths, which are then redirected into the building to further improve illumination. In some embodiments, the transparent substrate comprises a single wavelength conversion layer, wherein said wavelength conversion layer comprises a polymer matrix and at least one luminescent material. In some embodiments, the transparent substrate comprises two or more transparent layers, wherein at least one of the layers is a wavelength conversion layer, wherein said wavelength conversion layer comprises a polymer matrix and a luminescent material. In some embodiments, the wavelength conversion layer or layers may be in between glass or polymer plates, wherein the glass or polymer plates also act to internally reflect and refract photons towards the edge surface. In some embodiments, the wavelength conversion layer or layers may be on top of or on bottom of a glass or polymer plate, wherein the glass or polymer plate also acts to internally reflect and refract photons towards the edge surface. [0013] The transparent composite comprising a holographic element and a transparent substrate, as described herein, may include additional layers. For example, the transparent composite may comprise an adhesive layer in between the holographic element and transparent substrate. Some embodiments the system may also comprise additional glass or polymer layers. In some embodiments, the additional glass or polymer layers may be incorporated into the transparent substrate, to sandwich a wavelength conversion layer and protect it from environmental elements. In some embodiments, the additional glass or polymer layers may be used which encapsulate the holographic elements, or may be placed on top of the wavelength conversion layer. The glass or polymer layers may be configured to protect and prevent oxygen and moisture penetration into the wavelength conversion layer. In some embodiments, the glass or polymer layers may be used to internally refract or reflect photons that are emitted from the holographic element. In some embodiments, the system may further comprise a polymer layer comprising a UV absorber, configured to prevent harmful high energy photons from transmitting through the window into the building and/or contacting the wavelength conversion layer. In some embodiments, it may also be possible to combine layers to optimize different advantages together into one device.

[0014] The transparent composite may further comprise a photovoltaic or solar cell. The transparent composite may be configured for different types of solar energy conversion devices. In some embodiments of the transparent composite, the photovoltaic cell is attached to the edge surface of the transparent composite, and the photovoltaic cell absorbs a portion of the light that is diffracted by the holographic element. In some embodiments of the transparent composite, the photovoltaic cell is attached to the edge surface of the transparent composite, and the photovoltaic cell absorbs a portion of the light that is absorbed by the luminescent material and re-emitted at a different wavelength. In some embodiments, the solar energy conversion device is a silicon-based device, a III-V or II- VI PN junction device, a Copper-Indium-Gallium-Selenium (CIGS) thin-film device, an organic sensitizer device, an organic thin-film device, or a Cadmium Sulfide/Cadmium Telluride (CdS/CdTe) thin- film device. In some embodiments, the photovoltaic device or solar cell may be an amorphous Silicon (a-Si) solar cell. In some embodiments, the photovoltaic device or solar cell comprises a microcrystalline Silicon ^c-Si) solar cell. In some embodiments, the photovoltaic device or solar cell may be a crystalline Silicon (c-Si) solar cell.

[0015] These and other embodiments are described in greater detail below. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] FIG. 1 illustrates the viewing angle of an embodiment of a transparent composite.

[0017] FIG. 2 shows a schematic of an embodiment of the transparent composite comprising a holographic element and a transparent substrate.

[0018] FIG. 3 shows a schematic of an embodiment of the transparent composite comprising a holographic element and a transparent substrate.

[0019] FIG. 4 shows a schematic of an embodiment of the transparent composite comprising a holographic element and a transparent substrate.

[0020] FIG. 5 shows a schematic of an embodiment of the transparent composite comprising a holographic element, a transparent substrate, and a wavelength conversion layer.

[0021] FIG. 6 shows a schematic of an embodiment of the transparent composite comprising a holographic element, a transparent substrate, a wavelength conversion layer, and a solar energy conversion device.

[0022] FIG. 7 shows a transmission spectrum of HOE/WLC film vs. different incident light wavelength at the incident angle of 0° towards the sample normal.

[0023] FIG. 8 shows the diffraction efficiency of HOE/WLC film vs. different incident light wavelength at the incident angle of 50° towards the sample normal.

[0024] FIG.9 shows the results of the sunlight redirecting experiment of the HOE/WLC film.

DETAILED DESCRIPTION

[0025] Since sunlight often enters windows at a downward angle, much of the light is not useful in illuminating a room, and the light that does enter the room typically falls in one spot on the floor near the window. This unguided light in office buildings often causes glaring on computer screens and is essentially wasted on undesired areas. However, if the incoming downward light rays can be redirected upward, such that they strike the ceiling, the light can be more usefully employed in lighting the room.

[0026] In particular, the embodiments described herein are useful for window based building applications. For window-based systems, the currently available products cannot provide high transparency, reduced glare, and improved natural illumination uniformity throughout the room. The disclosed transparent composite uses holographic elements to redirect a portion of the incoming solar radiation into the building at an angle that improves the illumination and reduces glaring while maintaining a clear transparent window (>70% transmittance of visible wavelengths).

[0027] Holographic elements or holographic optical elements (HOEs) are holograms that consist of a diffraction pattern rendered as a surface relief, or a thin film containing an index modulation throughout the thickness of the film. HOEs are typically produced on a glass plate coated with a film of dichromated gelatin emulsion by exposing it to two mutually coherent laser beams, referred to as object and reference beams. HOEs have been employed to act as concentrators of incoming solar radiation. U.S. Patent No. 5,517,339 discloses a method of manufacturing holographic optical elements. U.S. Patent Nos. 5,877,874; 6,274,860; and 6,469,241 disclose holographic concentrator devices used to separate and concentrate optical radiation. U.S. Patent Application No. 61/903,317 to Nitto Denko Inc. discloses solar energy collection systems utilizing holographic optical elements useful for building integrated photovoltaics. All of the foregoing citations are hereby incorporated by reference in their entireties. In some embodiments, a holographic optical element comprises diffractive elements having varying indices of refraction. When confronted by light of certain angles, the varying indices of refraction of the diffractive elements produce a diffraction pattern that directs the light into the building at an angle that provides improved illumination within the building.

[0028] In some embodiments, the transparent composite comprises at least one holographic element and a transparent substrate. In some embodiments, the holographic element and the transparent substrate of the transparent composite are transparent such that they provide little to no visibility distortion which makes the transparent composite highly useful for window-based building applications. In some embodiments, the holographic element comprises an interference pattern that diffracts a selected portion of the incident solar light such that the light is redirected into the building at an angle that provides improved illumination within the building.

[0029] In some embodiments, the diffractive structures are the same across the area defined by the surface of the holographic element. In some embodiments, the diffractive structures continuously vary across the area defined by the surface of the holographic element. In some embodiments, the holographic element is configured with multiple diffractive structures. In some embodiments, the diffractive structures of the holographic element vary throughout the area defined by the surface of the holographic element, such that light incident on one side of the holographic element is diffracted into the transparent substrate at a different angle than the light incident on a different side of the holographic element. In some embodiments, the diffractive structures of the holographic element are continuously varying throughout the area defined by the surface of the holographic element. The direction of diffraction for any given angle with respect to the holographic optical element can be controlled based upon angular the position of the two coherent laser beams used to record a hologram of the holographic optical element.

[0030] Solar radiation is directly incident on building windows (which are vertical) at an angle equal to or greater than 0 degrees from horizontal. Therefore, in some embodiments it may only be necessary to configure the holographic optical element to diffract light that is incident on the window at angles greater than 0 degrees from horizontal, or from the direction normal to the face of the window, in order to provide adequate indoor illumination. In some embodiments of the transparent composite, the transparent composite is transparent for a viewing angle of about +20 degrees to about -90 degrees, about +40 degrees to about -90 degrees, about +50 degrees to about -90 degrees, about +75 degrees to about -90 degrees from horizontal, or from the direction normal to the face of the window.

[0031] In order for the transparent composite to be applicable to building window based applications, the transparent composite may be transparent in at least one viewing angle, or objects may be recognizable when viewed through the transparent composite, to provide undistorted viewing of the scenery through the window. The transmittance of visible light (wavelengths of light between about 400 nm and about 700 nm) through the transparent composite is a good indicator of transparency. In some embodiments, the transparent composite has a transmittance of at least 50%, at least 60%, at least 70%, at least 80%, or at least 90% for wavelengths of light between about 400 nm and about 700 nm, for the required viewing angle of the application.

[0032] The transparent composite may be configured to be transparent at a variety of viewing angles depending on the application and/or location of the window in the building, and/or the longitudinal location of the building. In some embodiments, the transparent composite is transparent for a viewing angle of 0 degrees (i.e., the transparent composite is transparent when looking straight through the window as illustrated in FIG. 1). In some embodiments, the transparent composite may be placed vertically, such as a window in a building. In some embodiments of the transparent composite which is placed vertically, the transparent composite is transparent for a viewing angle of about +20 degrees to about -20 degrees, about +40 degrees to about -40 degrees, about +60 degrees to about -60 degrees, or about +90 degrees to about -90 degrees from horizontal, or from the direction normal to the face of the window. In some embodiments, the transparent composite may be placed horizontally, such as a sky light in a building. In some embodiments of the transparent composite which is place horizontally, the transparent composite is transparent for a viewing angle of about +20 degrees to about -20 degrees, about +40 degrees to about -40 degrees, about +60 degrees to about -60 degrees, or about +90 degrees to about -90 degrees from vertical, or from the direction normal to the face of the window. In some embodiments, the transparent composite may be placed at an angle other than horizontal or vertical, in which case, the transparent composite may be designed to be transparent for a viewing angle depending on the particular application.

[0033] In some embodiments, the holographic element is configured to diffract photons into the transparent substrate at a different angle depending on the incident wavelength. It may be desirable to configure the holographic element of the transparent composite to diffract portions of the light spectrum at different angles. In some embodiments, the diffractive portion of the light spectrum to be diffracted at different angles can be visible light or portions of the visible light spectrum. In some embodiments, the portion of the light spectrum to be diffracted include from about 400 nm to about 700 nm. In some embodiments, for instance, for building applications, it may be desirable to not allow UV and IR wavelengths into the building (UV and IR photons do not provide illumination, but they are absorbed and converted into heat, which increases the heat removal requirements). In some embodiments, the holographic element may be configured to diffract visible light (400 nm to about 700 nm) into the building at such an angle, for example upwards towards the ceiling, such that the indoor illumination is improved. In some embodiments, the holographic element may be configured to diffract all visible light into the building such that the indoor illumination is improved, while diffracting all incident UV and IR photons at an angle that prevents these photons from entering the building. For some applications, the viewing angle required from the inside may be very small, such as +/- 5 degrees from horizontal, in which case the holographic element may be configured to diffract visible light with incoming angles greater than +5 degrees or less than -5 degrees from horizontal, and redirect this light into the building at an angle that improves the indoor illumination. In this manner, the amount of light that is redirected into useful illumination within the building is maximized, while also maintaining the visibility requirements for the particular application. In some embodiments, the holographic element may be optimized to diffract or not diffract different portions of the light spectrum at different angles depending on the application of the transparent composite. In some embodiments, the holographic element is configured to diffract all incident UV wavelengths at an angle that prevents these photons from entering the building. In some embodiments, the holographic element is configured to diffract all incident IR wavelengths at an angle that prevents these photons from entering the building. In some embodiments, the holographic element is configured to diffract only incident visible wavelengths of greater than 80 degrees, greater than 60 degrees, greater than 30 degrees, or greater than 5 degrees, greater than 80 degrees or less than -80 degrees, greater than 60 degrees or less than -60 degrees, greater than 30 degrees or less than -30 degrees, or greater than 5 degrees and less than -5 degrees (from horizontal) at an angle that redirects these photons into the building such that illumination is improved.

[0034] In some embodiments, the holographic element diffracts direct solar incident light upwards towards the ceiling of the building interior. In some embodiments, 10% to 95% of the direct solar incident light is directed towards the ceiling. In some embodiments, the amount of direct solar incident light diffracted towards the ceiling may be about 10%, 15%, 20%, 25%, 30%, 35%, or 40% to about 50%, 60%, 70%, 80%, 90%, or 95%, and/or any combination of the aforementioned values of the direct solar incident light is directed towards the ceiling. In some embodiments, the direct solar incident light may be the visible light component of the incident light. In some embodiments, the visible light can be between about 400 nm to about 700 nm wavelength radiation. In some embodiments, the holographic element is configured to diffract visible wavelengths upwards at an angle of about 30°, 35°, 40°, 45° to about 55°, 60°, 65°, 70°. The amount of improved illumination upon the desired surface, e.g., the ceiling, can be determined by methods known in the art, e.g., Thanachareonkit, A., et al, Empirical assessment of a prismatic daylight-redirecting window film in a full-scale office test bed, Proceedings of Illuminating Engineering Society Annual Conference (IESNA)(October 23-24, 2013), pp 63-81, which is hereby incorporated by reference in its entirety. Those skilled in the art will recognize that the angle of incident light will vary based on geographic location and will make appropriate adjustments.

[0035] In some embodiments, the holographic element is positioned within the top or upper portion of a vertically oriented substrate. In some embodiments, the positioning of the holographic element within the top or upper portion of the vertically oriented substrate (e.g., a window) may diffuse the broad band visible light to the ceiling and out of the sight line of persons within the building. In some embodiments, the holographic element is disposed above the desired line of sight height, e.g., about 6 feet above the ground/floor level.

[0036] In some embodiments of the transparent composite, the holographic element comprises at dichromated gelatin, photopolymer, bleached, and unbleached photo emulsion, nanoparticle doped photopolymer, or any combination thereof.

[0037] In some embodiments of the transparent composite, the transparent substrate comprises transparent glass or polymer materials with a refractive index of between about 1.4 and about 1.7.

[0038] In some embodiments of the transparent composite, the transparent substrate comprises one or multiple transparent layers.

[0039] In some embodiments of the transparent composite, the transparent substrate comprises at least one layer formed from a substance selected from the group consisting of polyethylene terephthalate, polymethyl methacrylate, polyvinyl butyral, ethylene vinyl acetate, ethylene tetrafluoroethylene, polyimide, amorphous polycarbonate, polystyrene, siloxane sol-gel, polyurethane, polyacrylate, and combinations thereof. In some embodiments of the transparent composite, the transparent substrate comprises at least one layer comprising one host polymer, a host polymer and a co-polymer, or multiple polymers. In some embodiments of the transparent composite, the transparent substrate comprises at least one layer of a transparent inorganic amorphous glass. In some embodiments of the transparent composite, the transparent substrate comprises at least one layer of a glass material selected from the group consisting of silicon dioxide, albite, crown, flint, low iron glass, borosilicate glass, soda-lime glass, or any combination thereof.

[0040] In some embodiments, a luminescent material is incorporated into the transparent composite. In some embodiments, the luminescent material acts to further enhance the indoor illumination. In some embodiments, the luminescent material may also act to prevent UV photons from entering the inside of the building. In some embodiments of the transparent composite, the transparent substrate further comprises a luminescent material, wherein said luminescent material acts to absorb incident photons of a particular wavelength range, and re-emit those photons at a different wavelength. In some embodiments, a portion of the re-emitted photons may be redirected into the holographic element, wherein the holographic element diffracts the re-emitted photons into the building at an angle which improves the indoor illumination. In some embodiments, a solar energy harvesting device may be placed at the edges of the transparent composite. In some embodiments, a portion of the photons re-emitted by the luminescent material may be internally reflected and refracted within the transparent substrate until they reach the edges of the substrate where they exit the transparent composite. In some embodiments, the luminescent material absorbs UV photons and converts these photons into visible wavelengths. In some embodiments, the luminescent material absorbs visible photons and converts these photons into lower energy visible wavelengths, which may be more easily converted into energy by a solar harvesting device.

[0041] In some embodiments of the transparent composite, the transparent substrate further comprises a luminescent material, wherein said luminescent material acts to absorb incident photons of a particular wavelength range, and re-emit those photons at a different wavelength. Depending on the application and the type of luminescent material that is utilized, it may be desirable to redirect the re-emitted photons into the building to further improve the indoor illumination. It may also be desirable to redirect the re-emitted photons towards the edges of the transparent composite or reflect them back out the top of the transparent composite so that they exit the system without increasing the heat inside the building. It may also be desirable to redirect the re-emitted photons towards the edges of the transparent composite so that they may be utilized by a solar energy harvesting device. In some embodiments, the transparent substrate comprises a single wavelength conversion layer, wherein said wavelength conversion layer comprises a polymer matrix and at least one luminescent material. In some embodiments, the transparent substrate comprises two or more transparent layers, wherein at least one of the layers is a wavelength conversion layer, wherein said wavelength conversion layer comprises a polymer matrix and a luminescent material. In some embodiments, the wavelength conversion layer or layers may be sandwiched in between glass or polymer plates, wherein the glass or polymer plates also act to internally reflect and refract photons as desired. In some embodiments, the wavelength conversion layer or layers may be on top of or on bottom of a glass or polymer plate, wherein the glass or polymer plate also acts to internally reflect and refract photons as desired. In some embodiments, the wavelength conversion layer may be placed on top of the holographic element, in between the holographic element and the transparent substrate, underneath the transparent substrate and the holographic element, or in any place as needed by the particular application.

[0042] The transparent composite comprising a holographic element and a transparent substrate, as described herein, may include additional layers. For example, the system may comprise an adhesive layer in between the holographic element and transparent substrate. In some embodiments the system may also comprise additional glass or polymer layers. In some embodiments, the additional glass or polymer layers may be incorporated into the transparent substrate, to sandwich a wavelength conversion layer and protect it from environmental elements. In some embodiments, the additional glass or polymer layers may be used which encapsulate the holographic elements, or may be placed on top of the wavelength conversion layer. The glass or polymer layers may be configured to protect and prevent oxygen and moisture penetration into the wavelength conversion layer. In some embodiments, the glass or polymer layers may be used to internally refract or reflect photons that are emitted from the holographic element. In some embodiments, the system may further comprise a polymer layer comprising a UV absorber, configured to prevent harmful high energy photons from transmitting through the window into the building and/or contacting the wavelength conversion layer. In some embodiments, it may also be possible to combine layers to optimize different advantages together into one device.

[0043] The diffractive structures employed in a holographic element act to diffract the incident light into the transparent substrate. The diffractive structures for each transparent composite may be optimized for the particular system, with regards to the size, shape of the system, and it's location on the building and latitude. In some embodiments of the transparent composite, the diffractive structures of the holographic element are different throughout the area defined by the surface of the holographic element. In some embodiments of the transparent composite, the multiple diffractive structures of the holographic element are configured to diffract a portion of the solar radiation at a different angle into the transparent substrate depending on the angle of incidence of the light onto the holographic element. In some embodiments of the transparent composite, the multiple diffractive structures of the holographic element are configured to minimize the loss of photons reflected out of the transparent substrate, so that the light transmitted through the window is maximized. In some embodiments, the holographic element may cover the entire light incident surface of the transparent substrate. In some embodiments, the holographic element may only cover a portion of the entire light incident surface of the transparent substrate.

[0044] In some embodiments of the transparent composite, the holographic element is configured to diffract photons into the transparent substrate at a different angle depending on the incident wavelength. For example, the holographic element may diffract UV and IR light at an angle that will allow reflection of the light out the edges or top of the transparent waveguide substrate, while at the same time the holographic element may diffract visible wavelengths into the inside of the building at an angle that improves the indoor illumination.

[0045] The holographic element may comprise various materials using methods known in the art. In some embodiments of the transparent composite, the holographic element comprises one or a multiplicity of materials, such as dichromated gelatin, photopolymer, bleached and unbleached photo emulsion, or any combination thereof.

[0046] Numerous methods may be used to manufacture the holographic element. Such methods have been described in the art, such as U.S. Patent Nos. 5,517,339; 5,877,874; 6,274,860; and 6,469,241, and U.S. Patent Application Publication Nos. 2010/0186818. All of the foregoing citations are hereby incorporated by reference in their entireties.

[0047] The holographic element is written into dichromated gelatin (DCG) which is fabricated using standard techniques know in the art (see B.J. Chang and CD. Leonard, Dichromated gelatin for the fabrication of holographic optical elements, Applied Optics, Vol. 18, Issue 14, pp. 2407 (1979), or http://holoinfo.no- ip.biz/wiki/index.php/Dichromated_Gelatin), which is hereby incorporated by reference in its entirety. In some embodiments, in-house deposition of DCG layers is performed because freshly prepared material can provide a high Δη useful for HOE efficient performance.

[0048] In some embodiments, the DCG can be rinsed after recording for an extended period of time to effect a swelling of the DCG/gelatin. In some embodiments, the DCG can be rinsed for a period of at least about 5 minutes, at least about 7 minutes, at least about 10 minutes, at least about 15 minutes to about 30 minutes, at least about 15 minutes to about 45 minutes and/or at least about 15 minutes to about 60 minutes. In one embodiment, the DCG can be rinsed for about 20 minutes.

[0049] The transparent matrix of the transparent substrate may comprise a material selected from a glass and a transparent polymer, or any material that is transparent and is compatible with the transparent composite. In some embodiments, the transparent matrix of the transparent substrate may need to be transparent to IR, UV, and/or visible light in various combinations. In some embodiments, the transparent matrix of the transparent substrate is transparent over a large section of the visible spectrum. For example, a suitable transparent polymer would be poly(methyl methacrylate) polymer (PMMA, which typically has a refractive index of about 1.49) or a polycarbonate polymer (typical refractive index of about 1.58). The glass may be any transparent inorganic amorphous material, including, but not limited to, glasses comprising silicon dioxide and glasses selected from the albite type, crown type and flint type. Some of these glasses have refractive indexes ranging from approximately 1.30 to 1.9. In some embodiments of the transparent composite, at least one layer of the transparent substrate comprises transparent glass or polymer materials with a refractive index of between about 1.4 and about 1.7.

[0050] In some embodiments of the transparent composite, the holographic element is incorporated into the transparent substrate. In some embodiments, the transparent substrate comprises an optically transparent polymer layer sandwiched in-between two glass plates, wherein the holographic element is incorporated into the optically transparent polymer layer. In some embodiments, the optically transparent polymer layer comprises an epoxy.

[0051] It is also possible to further enhance the transparent composite by employing luminescent materials. Therefore, in some embodiments of the transparent composite, the transparent composite further comprises a luminescent material, wherein said luminescent material acts to absorb incident photons of a particular wavelength range, and re-emit those photons at a different wavelength. In some embodiments, the re-emitted photons may be redirected into the holographic element where they are diffracted into the inside of the building at an angle to improve the indoor illumination. In some embodiments, the re- emitted photons may be internally reflected and refracted within the transparent substrate until they reach the edges where they exit the transparent composite. The application of a holographic element in conjunction with a transparent substrate comprising a luminescent material may enhance the indoor illumination effect of the transparent composite. In some embodiments, the holographic element is configured to diffract the visible portions of the solar spectrum into the building at an angle that improves the indoor illumination. In some embodiments, the transparent substrate comprises at least one wavelength conversion layer. In some embodiments, the wavelength conversion layer is configured to convert photons of a particular wavelength to a more desirable wavelength that is more efficiently diffracted by the transparent composite.

[0052] In some embodiments, the transparent composite comprises a single wavelength conversion layer, wherein said wavelength conversion layer comprises a polymer matrix and at least one luminescent material. In some embodiments, the transparent composite comprises two or more transparent layers, wherein at least one of the layers is a wavelength conversion layer, wherein said wavelength conversion layer comprises a polymer matrix and a luminescent material. In some embodiments, the wavelength conversion layer or layers may be in-between glass or polymer plates, wherein the glass or polymer plates also act to reflect and refract photons as desired. In some embodiments, the wavelength conversion layer or layers may be on top of or on bottom of a glass or polymer plate, wherein the glass or polymer plate also acts to reflect and refract photons as desired.

[0053] The luminescent material can be dispersed inside the transparent matrix of the transparent substrate, deposited on at least one side of the transparent substrate, or in-between two separate transparent layers. In some embodiments, the transparent substrate comprises a single layer, wherein said layer is a wavelength conversion layer, wherein said wavelength conversion layer comprises a polymer matrix and at least one luminescent material. In some embodiments, the transparent substrate comprises two or more transparent layers, wherein at least one of the layers is a wavelength conversion layer, wherein said wavelength conversion layer comprises a polymer matrix and a luminescent material. In some embodiments, the wavelength conversion layer or layers may be sandwiched in between glass or polymer plates, wherein the glass or polymer plates also act to reflect and refract photons as desired. In some embodiments, the wavelength conversion layer or layers may be on top of or on bottom of a glass or polymer plate, wherein the glass or polymer plate also acts to reflect and refract photons as desired.

[0054] In some embodiments of the transparent composite, the holographic element is incorporated into the transparent substrate. In some embodiments, the transparent substrate comprises a wavelength conversion layer in-between two glass plates, wherein the holographic element is incorporated into the wavelength conversion layer, and wherein the wavelength conversion layer comprises a luminescent material and a polymer matrix. In some embodiments, the polymer matrix of the wavelength conversion layer comprises an epoxy.

[0055] In order for the transparent composite to be used in window based applications, the polymer matrix of the wavelength conversion layer may be transparent to allow for visibility. In some embodiments of the transparent composite, the polymer matrix of the wavelength conversion layer is formed from polyethylene terephthalate, polymethyl methacrylate, polyvinyl butyral, ethylene vinyl acetate, ethylene tetrafluoroethylene, polyimide, amorphous polycarbonate, polystyrene, siloxane sol-gel, polyurethane, polyacrylate, polyepoxide, or a combination thereof. In some embodiments of the transparent composite, the polymer matrix may comprise one host polymer, or a host polymer and a copolymer. In some embodiments of the transparent composite, the polymer matrix may comprise multiple polymers. [0056] In some embodiments, the polymer matrix material used in the wavelength conversion layer has a refractive index in the range of about 1.4 to about 1.7 or about 1.45 to about 1.55.

[0057] A luminescent material, sometimes referred to as a chromophore or fluorescent dye, is a compound that absorbs photons of a particular wavelength or wavelength range, and re-emits the photon at a different wavelength or wavelength range. Chromophores used in transparent composite media can greatly enhance the performance of solar cells and photovoltaic devices. However, such devices are often exposed to extreme environmental conditions for long periods of time, e.g., 20 years or more. As such, maintaining the stability of the chromophore over a long period of time may be important. In some embodiments, chromophore compounds with good photostability for long periods of time, e.g., 20,000 or more hours of illumination under one sun (AM1.5G) irradiation with <10% degradation, are preferably used in the transparent composite comprising a holographic element, a transparent substrate, and a wavelength conversion layer.

[0058] Luminescent materials can be up-converting or down-converting. In some embodiments, the luminescent material may be an up-conversion luminescent material, meaning a compound that converts photons from lower energy (long wavelengths) to higher energy (short wavelengths). Up-conversion dyes may include rare earth materials which have been found to absorb photons of wavelengths in the infrared (IR) region, ~97 5nm, and re-emit in the visible region (400-700 nm), for example, Yb ³⁺ , Tm ³⁺ , Er ³⁺ , Ho ³⁺ , and NaYF ⁴ . Additional up-conversion materials are described in U.S. Patent Nos. 6,654, 161 and 6, 139,210, and in the Indian Journal of Pure and Applied Physics, volume 33, pages 169-178, (1995), which are hereby incorporated by reference in their entireties. In some embodiments, the luminescent material may be a down-shifting luminescent material, meaning a compound that converts photons of high energy (short wavelengths) into lower energy (long wavelengths). In some embodiments, the down-shifting luminescent material may be a derivative of perylene, benzotriazole, or benzothiadiazole, as are described in U.S. Provisional Patent Application Nos. 61/430,053; 61/485,093; and 61/539,392, which are herby incorporated by reference in their entireties. In some embodiments, the wavelength conversion layer comprises both an up-conversion luminescent compound and a downshifting luminescent compound.

[0059] In some embodiments, the luminescent material is configured to convert incoming photons of a first wavelength to a different second wavelength. In some embodiments, the luminescent material is a down-shifting material. Various luminescent materials can be used. In some embodiments of the transparent composite, at least one of the luminescent materials is a quantum dot material. In some embodiments, the luminescent material is an organic dye. In some embodiments, the luminescent material is selected from perylene derivative dyes, benzotriazole derivative dyes, diazaborinine derivative dyes, or benzothiadiazole derivative dyes.

[0060] In some embodiments, the chromophore is an organic compound. In some embodiments, the chromophore is selected from perylene derivative dyes, benzotriazole derivative dyes, or benzothiadiazole derivative dyes. Examples of chromophores can be found in U.S. Patent Publication US2013/0074927, which is hereby incorporated by reference in its entirety.

[0061] It may be important that the transparent composite remain transparent for use in building window based applications. Luminescent materials in the UV wavelength spectrum are typically clear, and would not alter the color if used in the wavelength conversion transparent composite. In some embodiments, the transparent composite comprises a luminescent material that shifts wavelengths in the UV portion of the spectrum into the visible or IR portions of the spectrum. In some embodiments, the luminescent material is optimized to be highly absorbing in the UV and transparent in the visible portion of the solar spectrum. The luminescent material efficiency is independent of angle of incidence, allowing operation over a broad range of incidence angles.

[0062] In some embodiments, the luminescent material comprises an organic photostable chromophore. In some embodiments, the luminescent material comprises a structure as given by the following general formula (I):

wherein Ri, R ₂ , and R3 comprise optionally substituted alkyl, or optionally substituted aryl. Example compounds of general formula (I) include the following:

[0063] The term "alkyl" refers to a branched or straight fully saturated acyclic aliphatic hydrocarbon group (i.e., composed of carbon and hydrogen containing no double or triple bonds). Alkyls include, but are not limited to, methyl, ethyl, propyl, isopropyl, butyl, isobutyl, tertiary butyl, pentyl, hexyl, and the like.

[0064] The term "heteroalkyl" used herein refers to an alkyl group comprising one or more heteroatoms. When two or more heteroatoms are present, they may be the same or different.

[0065] The term "cycloalkyl" used herein refers to saturated aliphatic ring system moiety having three to twenty-five carbon atoms including, but not limited to, cyclopropyl, cyclopentyl, cyclohexyl, cycloheptyl, and the like.

[0066] The term "polycycloalkyl" used herein refers to saturated aliphatic ring system moiety having multiple cylcoalkyl ring systems.

[0067] The term "alkenyl" used herein refers to a monovalent straight or branched chain moiety of from two to twenty-five carbon atoms containing at least one carbon double bond including, but not limited to, 1-propenyl, 2-propenyl, 2-methyl-l-propenyl, 1-butenyl, 2-butenyl, and the like.

[0068] The term "alkynyl" used herein refers to a monovalent straight or branched chain moiety of from two to twenty-five carbon atoms containing a carbon triple bond including, but not limited to, 1-propynyl, 1-butynyl, 2-butynyl, and the like.

[0069] The term "aryl" used herein refers to homocyclic aromatic moiety whether one ring or multiple fused rings. Examples of aryl groups include, but are not limited to, phenyl, naphthyl, phenanthrenyl, naphthacenyl, fluorenyl, pyrenyl, and the like. Further examples include:

pyren-1-yl perylen-3-yl 9H-fluoren-2-yl

[0071] The term "alkaryl" or "alkylaryl" used herein refers to an alkyl-substituted aryl moiety. Examples of alkaryl include, but are not limited to, ethylphenyl, 9,9-dihexyl- 9H-fluorene, and the like.

[0072] The term "aralkyl" or "arylalkyl" used herein refers to an aryl-substituted alkyl moiety. Examples of aralkyl include, but are not limited to, phenylpropyl, phenylethyl, and the like.

[0073] The term "heteroaryl" used herein refers to an aromatic group comprising one or more heteroatoms, whether one ring or multiple fused rings. When two or more heteroatoms are present, they may be the same or different. In fused ring systems, the one or more heteroatoms may be present in only one of the rings. Examples of heteroaryl groups include, but are not limited to, benzothiazyl, benzoxazyl, quinazolinyl, quinolinyl, isoquinolinyl, quinoxalinyl, pyridinyl, pyrrolyl, oxazolyl, indolyl, thiazyl and the like. Further exam les of substituted and unsubstituted heteroaryl rings include:

pyridin-2-yl pyridin-4-yl 2-cyanopyridin-5-yl pyridazin-3-yl pyridazin-4-yl

pyrimidin-2-yl pyrimidin^-yl pyrazin-2-yl triazin-2-yl

quinolin-2-yl quinolin-4-yl quinolin-6-yl isoquinolin-1 -yl quinazolin

benzofuran-2-yl benzothiophen-2-yl 9H-carbazol-2yl dibenzofuran-4-yl dibenzothiophen-4-yl

[0074] The term "alkoxy" used herein refers to straight or branched chain alkyl moiety covalently bonded to the parent molecule through an— O— linkage. Examples of alkoxy groups include, but are not limited to, methoxy, ethoxy, propoxy, isopropoxy, butoxy, n-butoxy, sec -butoxy, t-butoxy and the like.

[0075] The term "heteroatom" used herein refers to any atom that is not C (carbon) or H (hydrogen). Examples of heteroatoms include S (sulfur), N (nitrogen), and O (oxygen).

[0076] The term "cyclic amino" used herein refers to either secondary or tertiary amines in a cyclic moiety. Examples of cyclic amino groups include, but are not limited to, aziridinyl, piperidinyl, N-methylpiperidinyl, and the like.

[0077] The term "cyclic imido" used herein refers to an imide in the moiety of which the two carbonyl carbons are connected by a carbon chain. Examples of cyclic imide groups include, but are not limited to, 1,8-naphthalimide, pyrrolidine-2,5-dione, lH-pyrrole-2,5- dione, and the like.

[0078] The term "alcohol" used herein refers to a moiety -OH. [0079] The term "acyl" used herein refers to a moiety -C(=0)R.

[0080] The term "aryloxy" used herein refers to an aryl moiety covalently bonded to the parent molecule through an— O— linkage.

[0081] The term "acyloxy" used herein refers to a moiety -0-C(=0)R.

[0082] The term "carbamoyl" used herein refers to a moiety -C(=0)NH ₂ .

[0083] The term "carbonyl" used herein refers to a functional group C=0.

[0084] The term "carboxy" used herein refers to a moiety -COOR.

[0085] The term "ester" used herein refers to a functional group RC(=0)OR' .

[0086] The term "amido" used herein refers to a moiety -C(=0)NR'R".

[0087] The term "amino" used herein refers to a moiety -NR'R".

[0088] The term "heteroamino" used herein refers to a moiety -NR'R" wherein R' and/or R" comprises a heteroatom.

[0089] The term "heterocyclic amino" used herein refers to either secondary or tertiary amines in a cyclic moiety wherein the group further comprises a heteroatom.

[0090] The term "cycloamido" used herein refers to an amido moiety of- C(=0)NR'R" wherein R' and R" are connected by a carbon chain.

[0091] The term "sulfone" used herein refers to a sulfonyl moiety of -S(=0)2R.

[0092] The term "sulfonamide" used herein refers to a sulfonyl group connected to an amine group, the moiety of which is -S(=0)2-NR'R".

[0093] As used herein, a substituted group is derived from the unsubstituted parent structure in which there has been an exchange of one or more hydrogen atoms for another atom or group. When substituted, the substituent group(s) is may be, individually and independently, C1-C25 alkyl, C2-C25 alkenyl, C2-C25 alkynyl, C3-C25 cycloalkyl (optionally substituted with a moiety selected from the group consisting of halo, alkyl, alkoxy, alcohol, carboxyl, haloalkyl, CN, OH, -SCValkyl, -CF ₃ , and -OCF ₃ ), cycloalkyl geminally attached, C1-C25 heteroalkyl, C3-C25 heterocycloalkyl (e.g., tetrahydrofuryl) (optionally substituted with a moiety selected from the group consisting of halo, alkyl, alkoxy, alcohol, carboxyl, CN, -SCValkyl, -CF ₃ , and -OCF ₃ ), aryl (optionally substituted with a moiety selected from the group consisting of halo, alkyl, arylalkyl, alkoxy, alcohol, aryloxy, carboxyl, amino, imido, amido (carbamoyl), optionally substituted cyclic imido, cylic amido, CN, -NH- C(=0)-alkyl, -CF ₃ -OCF ₃ , and aryl optionally substituted with C1-C25 alkyl), arylalkyl (optionally substituted with a moiety selected from the group consisting of halo, alkyl, alkoxy, alcohol, aryl, carboxyl, CN, -SC -alkyl, -CF ₃ , and -OCF ₃ ), heteroaryl (optionally substituted with a moiety selected from the group consisting of halo, alkyl, alkoxy, alcohol, aryl, heteroaryl, aralkyl, carboxyl, CN, -S0 ₂ -alkyl, -CF ₃ , and -OCF ₃ ), halo (e.g., chloro, bromo, iodo and fluoro), cyano, hydroxy, optionally substituted cyclic imido, amino, imido, amido, -CF3, C1-C25 alkoxy (optionally substituted with halo, alkyl, alkoxy, aryl, carboxyl, CN, OH, -SCValkyl, -CF ₃ , and -OCF ₃ ), aryloxy, acyloxy, sulfhydryl (mercapto), halo(Ci- C6)alkyl, C1-C6 alkylthio, arylthio, mono- and di-(Ci-C6)alkyl amino, quaternary ammonium salts, amino(Ci-C6)alkoxy, hydroxy(Ci-C6)alkylamino, amino(Ci-C6)alkylthio, cyanoamino, nitro, carbamoyl, keto(oxy), carbonyl, carboxy, acyl, glycolyl, glycyl, hydrazino, guanyl, sulfamyl, sulfonyl, sulfinyl, thiocarbonyl, thiocarboxy, sulfonamide, ester, C-amide, N- amide, N-carbamate, O-carbamate, urea, and combinations thereof. Wherever a substituent is described as "optionally substituted" that substituent can be substituted with the above substituents.

[0094] In some embodiments, the first chromophore comprises a structure as given by the following formula (Il-a) or (Il-b):

wherein R ³ is selected from the group consisting of optionally substituted alkyl, optionally substituted alkenyl, optionally substituted cycloalkyl, optionally substituted heteroalkyl, optionally substituted aryl, optionally substituted heteroaryl, optionally substituted alkoxyalkyl, optionally substituted heteroalkenyl, optionally substituted arylalkyl, optionally substituted heteroaryl, optionally substituted cycloalkenyl, optionally substituted cycloheteroalkyl, optionally substituted cycloheteroalkenyl, optionally substituted amino, optionally substituted amido, optionally substituted cyclic amido, optionally substituted cyclic imido, optionally substituted alkoxy, optionally substituted carboxy, optionally substituted carbonyl, optionally substituted ether, optionally substituted ketone, optionally substituted sulfone, and optionally substituted sulfonamide; or R ³ is an optionally substituted polycyclic ring system, wherein each ring is independently cycloalkyl, aryl, heterocycloalkyl, or heteroaryl; R ⁴ , R ⁵ , and R ⁶ are independently selected from the group consisting of optionally substituted alkyl, optionally substituted alkenyl, optionally substituted cycloalkyl, optionally substituted heteroalkyl, optionally substituted aryl, optionally substituted heteroaryl, optionally substituted alkoxyalkyl, optionally substituted heteroalkenyl, optionally substituted arylalkyl, optionally substituted heteroaryl, optionally substituted heteroarylalkyl, optionally substituted cycloalkenyl, optionally substituted cycloheteroalkyl, optionally substituted cycloheteroalkenyl, optionally substituted amino, optionally substituted amido, optionally substituted cyclic amido, optionally substituted cyclic imido, optionally substituted alkoxy, optionally substituted carboxy, optionally substituted carbonyl, optionally substituted ether, optionally substituted ketone, optionally substituted sulfone, and optionally substituted sulfonamide; or R ⁴ and R ⁵ , R ⁴ and R ⁶ , R ⁵ and R ⁶ , or R ⁴ and R ⁵ and R ⁶ , together form an optionally substituted ring or an optionally substituted polycyclic ring system, wherein each ring is independently cycloalkyl, aryl, heterocyclalkyl, or heteroaryl; and L is selected from the group consisting of optionally substituted alkyl, optionally substituted heteroalkyl, optionally substituted alkylene, optionally substituted heteroalkylene, optionally substituted alkynylene, optionally substituted arylene, and optionally substituted heteroarylene.

[0095] In some embodiments, R ³ in formula Il-a and formula Il-b is selected from the group consisting of C _1-2 s alkyl, C _1-2 s heteroalkyl, C ₂ -25 alkenyl, C3-25 cycloalkyl, polycycloalkyl, heterocycloalkyl, arylalkyl; and R ³ may be optionally substituted with one or more of any of the following substituents: C _1-2 s alkyl, C _1-2 s heteroalkyl, C2-25 alkenyl, C3-25 cycloalkyl, polycycloalkyl, heterocycloalkyl, aryl, heteroaryl, OH, C _m H _2m+ iO ether, C _m H2m ₊ iCO ketone, C _m H _2m+ iC0 ₂ carboxylic ester, C _m H _2m+ iOCO carboxylic ester, ArO aryloxy, ArCO aryl ketone, ArC0 ₂ ester of aryl-carboxylic acid, ArOCO carboxylic ester of phenol, (C _m H _2m+ i)(C _p H _2p+ i)N amine, c-(CH ₂ ) _s amine, (C _m H _2m+ i)(C _p H _2p+ i) CO amide, c- (CH ₂ ) _s NCO amide, C _m H _2m+ iCON(C _p H ₂ p ₊ i) amide, CN, C _m H _2m+ iS0 ₂ sulfone, (C _m H2 _m+ i)(CpH2p ₊ i) S02 sulfonamide, C _m H2 _m+ iS02 (C _p H2 _P+ i) sulfonamide, or c- (CH2) _S S02 sulfonamide, wherein m is an integer in the range of 1 to 20, p is an integer in the range of 1 to 20, s is an integer in the range of 2 to 6, and Ar is any aromatic or heteroaromatic ring. R ⁴ , R ⁵ , and R ⁶ in formula Il-a and formula Il-b are independently selected from the group consisting of C _1-2 s alkyl, C _1-2 s heteroalkyl, C ₂ -25 alkenyl, C3-25 cycloalkyl, polycycloalkyl, heterocycloalkyl, aryl, heteroaryl, arylalkyl, heteroarylalkyl, C02C _m H _2m+ i carboxylic ester, (C _m H2 _m+ i)(C _p H2p ₊ i) CO amide, c-(CH ₂ ) _s NCO amide, COC _m H _2m+ i ketone, COAr, S0 ₂ C _m H _2m+ i sulfone, S0 ₂ Ar sulfone, (C _m H2 _m+ i)(C _p H2 _P+ i)S02 sulfonamide, c-(CH2) _s S02 sulfonamide; and R ⁴ , R ⁵ , and R ⁶ are independently optionally substituted with one or more of any of the following substituents: C _1-2 s alkyl, C _1-2 s heteroalkyl, C ₂ -25 alkenyl, C3-25 cycloalkyl, polycycloalkyl, heterocycloalkyl, aryl, heteroaryl, OH, C _m H _2m+ iO ether, C _m H _2m+ iCO ketone, C _m H _2m+ iC0 ₂ carboxylic ester, C _m H _2m+ iOCO carboxylic ester, ArO aryloxy, ArCO aryl ketone, ArC02 ester of aryl carboxylic acid, ArOCO carboxylic ester of phenol, (C _m H _2m+ i)(C _p H _2p+ i) amine, c-(CH ₂ ) _s N amine, (C _m H _2m+ i)(C _p H _2p+ i)NCO amide, c-(CH ₂ ) _s NCO amide, C _m H _2m+ iCON(C _p H _2p+ i) amide, C _m H _2m+ iS02 sulfone, (C _m H2 _m+ i)(C _p H2 _P+ i) S02 sulfonamide, C _m H2 _m+ iS02 (C _p H2 _P+ i) sulfonamide, or c-(CH ₂ ) _s NS0 ₂ sulfonamide, wherein m is an integer in the range of 1 to 20, p is an integer in the range of 1 to 20, s is an integer in the range of 2 to 6, and Ar is any aromatic or heteroaromatic ring. L in formula Il-b is selected from the group consisting of Ci-25 alkyl, C _1-2 s heteroalkyl, C2-25 alkenyl; and L may be optionally substituted with one or more of any of the following substituents: C _1-2 s alkyl, C _1-2 s heteroalkyl, C ₂ -25 alkenyl, C3-25 cycloalkyl, polycycloalkyl, heterocycloalkyl, aryl, heteroaryl, OH, C _m H _2m+ iO ether, C _m H2m ₊ iCO ketone, C _m H _2m+ iC0 ₂ carboxylic ester, C _m H _2m+ iOCO carboxylic ester, ArO aryloxy, ArCO aryl ketone, ArC0 ₂ ester of aryl-carboxylic acid, ArOCO carboxylic ester of phenol, (C _m H _2m+ i)(C _p H _2p+ i)N amine, c-(CH ₂ ) _s amine, (C _m H _2m+ i)(C _p H _2p+ i) CO amide, c- (CH ₂ ) _s NCO amide, C _m H _2m+ iCON(CpH ₂ p ₊ i) amide, CN, C _m H _2m+ iS0 ₂ sulfone, (C _m H2 _m+ i)(CpH2p ₊ i) S02 sulfonamide, C _m H2 _m+ iS02 (C _p H2 _P+ i) sulfonamide, or c- (CH2) _S S02 sulfonamide, wherein m is an integer in the range of 1 to 20, p is an integer in the range of 1 to 20, s is an integer in the range of 2 to 6, and Ar is any aromatic or heteroaromatic ring.

[0096] In some embodiments, R ³ in formula Il-a and formula Il-b is selected from the group consisting of C _1-2 s alkyl, C _1-2 s heteroalkyl, C ₂ -25 alkenyl, C3-25 cycloalkyl, C5-25 polycycloalkyl, C _1-2 s heterocycloalkyl, C _1-2 s arylalkyl; R ⁴ , R ⁵ , and R ⁶ are independently optionally substituted with one or more of any of the following substituents: C _1-2 s alkyl, C _1-2 s heteroalkyl, C2-25 alkenyl, C3-25 cycloalkyl, C _1-2 s aryl, and C _1-2 s heteroaryl.

[0097] In some embodiments, the first chromophore is:

[0098] In some embodiments, the luminescent material is present in the polymer matrix of the wavelength conversion layer in an amount in the range of about 0.01 wt% to about 10 wt%, about 0.01 wt% to about 3 wt%, about 0.05 wt% to about 2 wt%, or about 0.1 wt% to about 1 wt%, by weight of the polymer matrix.

[0099] In some embodiments of the transparent composite, the thickness of the wavelength conversion layer is about 2 μιη to about 50 μιη, about 5 μιη to about 20 μιη, about 8 to about 10 μιη, about 10 μιη to about 2 mm, or about 50 μιη to about 1 mm.

[0100] In some embodiments, the wavelength conversion layer comprises more than one luminescent material, for example, at least two different luminescent materials. In some embodiments of the transparent composite, the two or more luminescent materials absorb photons in the UV wavelength region. It may be desirable to have multiple luminescent materials in the wavelength conversion layer, depending on the application. In some embodiments, a first chromophore may act to convert photons having wavelengths in the range of about 300 nm to about 350 nm into photons of a wavelength of about 450 nm, and a second chromophore may act to convert photons having wavelengths in the range of about 350 nm to about 400 nm into photons of a wavelength of about 450 nm. Particular wavelength control may be selected based upon the luminescent material(s) utilized.

[0101] Various configurations of the luminescent materials in the transparent composite are possible. In some embodiments of the transparent composite, the transparent substrate comprises two or more wavelength conversion layers, wherein each of the wavelength conversion layers independently comprises a different luminescent material such that each of the wavelength conversion layers absorbs photons at a different wavelength range. In some embodiments, two or more luminescent materials are mixed together within the same layer, such as, for example, in the wavelength conversion layer. In some embodiments, two or more luminescent materials are located in separate layers or sublayers within the system. For example, the wavelength conversion layer comprises a first luminescent material, and an additional polymer sublayer comprises a second luminescent material.

[0102] The holographic element can separate the incident light and diffract the separated light at different angles depending on the wavelength of the light. In some embodiments, the holographic element is configured to separate the solar spectrum into different wavelengths for multiple incident angles of incoming light. For example, light is incident on the solar module at different angles during the day, where in the morning the light is at a low angle, in the middle of the day the light may be directly above the module, and in the evening the light is again at a low angle. The holographic element may have multiple holograms to account for the different angles of incident light, and is therefore able to "passively" track the incident light, and separate the spectrum into different wavelengths. In some embodiments, the holographic element is configured to separate potentially harmful UV portions of the solar spectrum from the visible portion of the spectrum, such that the UV wavelengths are refracted out of the system without being transmitted through the window. In some embodiments, the holographic element is configured to separate the IR portion of the solar spectrum from the visible portion of the solar spectrum, such that light having IR wavelengths is refracted out of the system without being transmitted through the window.

[0103] The transparent composite may further comprise a photovoltaic or solar cell. The transparent composite may be configured for different types of solar energy conversion devices. In some embodiments of the transparent composite, the photovoltaic cell is attached to the edge surface of the transparent composite, and the photovoltaic cell absorbs a portion of the light that is diffracted by the holographic element and/or re-emitted by the luminescent material. In some embodiments, the solar energy conversion device is selected from the group consisting of a silicon-based device, a III-V or II- VI PN junction device, a Copper- Indium-Gallium-Selenium (CIGS) thin film device, an organic sensitizer device, an organic thin-film device, or a Cadmium Sulfide/Cadmium Telluride (CdS/CdTe) thin film device. In some embodiments, the photovoltaic device or solar cell may be an amorphous Silicon (a-Si) solar cell. In some embodiments, the photovoltaic device or solar cell comprises a microcrystalline Silicon ^c-Si) solar cell. In some embodiments, the photovoltaic device or solar cell may be a crystalline Silicon (c-Si) solar cell.

[0104] In some embodiments of the transparent composite, additional materials may be used, such as glass layers or polymer layers. The materials may be used to protect the holographic element. In some embodiments, glass layers selected from low iron glass, Borofloat®, borosilicate glass, or soda-lime glass, may be used in the transparent composite. In some embodiments, the composition of the glass or polymer layers may also further comprise a strong UV absorber to block harmful high energy radiation.

[0105] In some embodiments, additional materials or layers may be used such as edge sealing tape, frame materials, polymer materials, or adhesive layers to adhere additional layers to the device. In some embodiments, the device further comprises an additional polymer layer containing a UV absorber. In some embodiments, the transparent substrate further comprises a UV absorber.

[0106] In some embodiments of the transparent composite, the transparent composite further comprises a UV stabilizer, antioxidant, absorber, which may act to block high energy irradiation. In some embodiments of the transparent composite, the transparent composite further comprises means for binding the holographic element, the transparent substrate, and any additional layer in the transparent composite.

[0107] Multiple configurations of the transparent composite are also possible. In some embodiments, the holographic element 100 is optically attached to a transparent substrate 101, where incoming light 102 is incident on the holographic element, and is diffracted into the building at an angle which improves illumination, while light that does not contact the holographic element transmits directly through the window and is not useful for illumination (light hits one spot on the floor causing glaring), as illustrated in FIG. 2. In some embodiments, the holographic element is optically attached to a transparent substrate, where incoming light is incident on the holographic element, and is diffracted such that light at a certain angle (i.e., greater than +50 degrees from horizontal, or from the direction normal to the face of the window) are redirected into the building at an angle which improves illumination, while light that is incident on the window within the desired line of sight (i.e., angles less +30 from horizontal, or from the direction normal to the face of the window) are allowed to transmit through the window without diffraction by the holographic element, as illustrated in FIG. 3. In some embodiments, the holographic element is optically attached to a transparent substrate, where incoming light is incident on the holographic element, and is diffracted such that light of undesirable wavelengths are refracted directly out of the module, while the light within the line of sight and of desirable (i.e., visible) wavelengths are allowed to transmit through the window, as illustrated in FIGS. 3-6.

[0108] As shown in FIG 3, the exemplified system comprises a holographic element 100 attached to a transparent substrate 101, wherein the transparent substrate comprises a transparent matrix having a major top surface for receipt of solar radiation, a bottom surface, and at least one edge surface. The holographic element 100 is disposed on the transparent substrate, wherein light is incident on the transparent composite at different angles throughout the day and wherein the holographic element is configured to allow incident light 102 through the transparent composite that is within the viewers line of sight 103 so that this view is undistorted. Further, the holographic element is configured to diffract incident light 102 on the window outside of the viewer's line of sight, into the building such that the illumination within the building in improved

[0109] Another embodiment of the system is shown in FIG. 4, comprising a holographic element 100 attached to a transparent substrate 101, wherein the transparent substrate comprises a transparent matrix having a major top surface for receipt of solar radiation, a bottom surface, and at least one edge surface. The holographic element 100 is disposed on the transparent substrate, wherein light is incident on the transparent composite at different angles throughout the day and wherein the holographic element is configured to allow a portion of the desirable incident light (visible) 104 through the transparent composite that is within the viewers line of sight 103 so that this view is undistorted. The holographic element is configured to diffract the desirable incident light (visible) 104 which is outside the viewers line of sight, into the building such that the illumination within the building in improved. Further, the holographic element is configured to diffract the undesirable incident light (UV) 105 and (IR) 106 at an angle that allows the light to exit the system without being transmitted through the window, thus reducing the heat due to solar radiation inside the building.

[0110] Another embodiment of the system is shown in FIG. 5, comprising a holographic element 100 attached to a transparent substrate 101, wherein the transparent substrate comprises a transparent matrix having a major top surface for receipt of solar radiation, a bottom surface, and at least one edge surface. The holographic element 100 is disposed on the transparent substrate, wherein light is incident on the transparent composite at different angles throughout the day and wherein the holographic element is configured to allow a portion of the desirable incident light (visible) 104 through the transparent composite that is within the viewers line of sight 103 so that this view is undistorted. The holographic element is configured to diffract the desirable incident light (visible) 104 which is outside the viewers line of sight, into the building such that the illumination within the building in improved. Further, the holographic element is configured to diffract the undesirable incident light (UV) 105 and (IR) 106 at an angle that allows the light to exit the system without being transmitted through the window, thus reducing the heat due to solar radiation inside the building. The transparent composite further comprises a wavelength conversion layer 107 where a portion of the light (UV wavelengths) are absorbed by the luminescent material in the wavelength conversion layer and re-emitted from the wavelength conversion layer at a wavelength in the visible light spectrum, and the holographic element then redirects the visible wavelengths into the building such that illumination is improved. Another embodiment of the system is shown in FIG. 6, comprising a holographic element 100 attached to a transparent substrate 101, wherein the transparent substrate comprises a transparent matrix having a major top surface for receipt of solar radiation, a bottom surface, and at least one edge surface. The holographic element 100 is disposed on the transparent substrate, wherein light is incident on the transparent composite at different angles throughout the day and wherein the holographic element is configured to allow a portion of the desirable incident light (visible) 104 through the transparent composite that is within the viewers line of sight 103 so that this view is undistorted. The holographic element is configured to diffract the desirable incident light (visible) 104 which is outside the viewers line of sight, into the building such that the illumination within the building in improved. Further, the holographic element is configured to diffract the undesirable incident light (UV) 105 and (IR) 106 at an angle that allows the light to exit the system without being transmitted through the window, thus reducing the heat due to solar radiation inside the building or vehicle. The transparent composite further comprises a wavelength conversion layer 107 where a portion of the light (UV wavelengths) are absorbed by the luminescent material in the wavelength conversion layer and re-emitted from the wavelength conversion layer at a wavelength in the visible light spectrum, and the holographic element then redirects the visible wavelengths either into the building such that illumination is improved, or into the transparent substrate where it is internally reflected and refracted towards its edges and out of the transparent composite. The transparent composite further comprises a solar energy conversion device 108, which is positioned on the edge of the transparent substrate so that the portion of diffracted light may be collected and converted into energy by the solar energy conversion device. In some embodiments, the transparent composite comprising a holographic element, a transparent substrate, a wavelength conversion layer, and a solar energy conversion device may be optimized to maximize indoor illumination, visibility, and solar energy harvesting.

[0111] In some embodiments, the holographic element is optically attached to a transparent substrate, where the transparent substrate comprises at least one wavelength conversion layer, where incoming light is incident on the holographic element, is separated such that undesirable wavelengths are refracted directly out of the module, while the desirable (UV and visible) wavelengths are reflected at an angle into the transparent substrate, and the UV wavelengths are absorbed by the luminescent material in the wavelength conversion layer and re-emitted from the wavelength conversion layer at a wavelength in the visible light spectrum, and the transparent substrate then directs the visible wavelengths by total internal reflection into the solar energy conversion device, where they are converted into electricity.

[0112] The transparent composite comprising a holographic element and a transparent substrate, as disclosed herein, is applicable for all different types of solar cell devices. Devices, such as a silicon-based device, a III-V or II-VI PN junction device, a Copper- Indium-Gallium-Selenium (CIGS) thin-film device, an organic sensitizer device, an organic thin film device, or a Cadmium Sulfide/Cadmium Telluride (CdS/CdTe) thin- film device, can be used with the transparent composite. In some embodiments, the system comprises at least one photovoltaic device or solar cell comprising a Cadmium Sulfide/Cadmium Telluride solar cell. In some embodiments, the photovoltaic device or solar cell may be a Copper Indium Gallium Diselenide solar cell. In some embodiments, the photovoltaic or solar cell may be a III-V or II-VI PN junction device. In some embodiments, the photovoltaic or solar cell may be an organic sensitizer device. In some embodiments, the photovoltaic or solar cell may be an organic thin-film device. In some embodiments, the photovoltaic device or solar cell may be an amorphous Silicon (a-Si) solar cell. In some embodiments, the photovoltaic device or solar cell comprises a microcrystalline Silicon ^c-Si) solar cell. In some embodiments, the photovoltaic device or solar cell may be a crystalline Silicon (c-Si) solar cell.

[0113] In some embodiments, additional materials may be used, such as glass plates or polymer layers. The materials may be used to encapsulate the holographic element(s), or they may be used to protect or encapsulate the solar cell and/or wavelength conversion layer. In some embodiments, glass plates selected from low iron glass, borosilicate glass, or soda- lime glass, may be used in the system. In some embodiments of the system, the composition of the glass plate or polymer layers may also further comprise a strong UV absorber to block harmful high energy radiation into the solar cell.

[0114] In some embodiments of the system, additional materials or layers may be used such as edge sealing tape, frame materials, polymer materials, or adhesive layers to adhere additional layers to the system. In some embodiments, the system further comprises an additional polymer layer containing a UV absorber.

[0115] In some embodiments of the system, the composition of the wavelength conversion layer further comprises a UV stabilizer, antioxidant, or absorber, which may act to block high energy irradiation and prevent photo-degradation of the chromophore compound. In some embodiments, the thickness of the wavelength conversion layer is between about 10 μιη and about 2 mm.

[0116] Some embodiments of the transparent composite further provide a means for binding the holographic element and the transparent substrate, and any additional layer in the transparent composite. In some embodiments, the transparent composite further comprises an adhesive layer. In some embodiments, an adhesive layer adheres the holographic elements to glass plates, polymer layers, or to the wavelength conversion layer. Various types of adhesives may be used. In some embodiments, the adhesive layer comprises a substance selected from the group consisting of rubber, acrylic, silicone, vinyl alkyl ether, polyester, polyamide, urethane, fluorine, epoxy, ethylene vinyl acetate, and combinations thereof. The adhesive can be permanent or non-permanent. In some embodiments, the thickness of the adhesive layer is between about 1 μιη and 100 μιη. In some embodiments, the refractive index of the adhesive layer is in the range of about 1.4 to about 1.7.

[0117] In some embodiments, the wavelength conversion layer is formed by first synthesizing the chromophore/polymer solution in the form of a liquid or gel, applying the chromophore/polymer solution to a glass plate using standard methods of application, such as spin coating or drop casting, then curing the chromophore/polymer solution to a solid form (i.e., heat treating, UV exposure, etc.) as is determined by the formulation design. Once dry, the film can then be adhered to glass or polymer substrates. In some embodiments the wavelength conversion layer may be adhered to glass or polymer surfaces using an optically transparent and photostable adhesive and/or laminator. [0118] The object of this disclosure is to provide a transparent composite comprising a holographic element and a transparent substrate, which may be suitable for application to building windows or skylights. By using this transparent composite, we can expect improved indoor illumination with minimal visibility distortion.

EMBODIMENTS

[0119] The following embodiments are specifically contemplated:

Embodiment 1. A transparent composite comprising:

a transparent substrate coupled to a holographic element;

wherein the transparent composite has a size and shape suitable for use as a building window;

wherein the holographic element comprises an interference pattern that diffracts a selected portion of incident solar light such that, when the transparent composite is used as a building window, the selected portion of incident light is redirected into the building at an angle that provides improved illumination within the building.

Embodiment 2. The transparent composite of Embodiment 1, wherein the selected portion of the incident light is diffracted in a direction that is away from normal to a surface of the transparent composite which is contacted by the selected portion of the incident light. Embodiment 3. The transparent composite of Embodiment 1 or 2, wherein the holographic element comprises a hologram, wherein the hologram is made with a laser. Embodiment 4. The transparent composite of Embodiment 1, 2, or 3, wherein the interference pattern of the holographic optical element varies throughout an area defined by a surface of the holographic element.

Embodiment 5. The transparent composite of Embodiments 1, 2, 3, or 4, wherein the holographic element is configured to diffract photons of different incident wavelengths in different directions in order to improve the interior illumination of the building.

Embodiment 6. The transparent composite of Embodiment 1, 2, 3, 4, or 5, wherein the holographic element is configured to diffract photons in the visible light region in a direction that will improve illumination in the building while reducing glare.

Embodiment 7. The transparent composite of Embodiment 1, 2, 3, 4, 5, or 6, wherein the holographic element is configured to diffract light incident on the system at an angle greater than about +60 degrees from the direction normal to the surface of the transparent composite. Embodiment 8. The transparent composite of Embodiment 1, 2, 3, 4, 5, or 6, wherein the holographic element is configured to diffract light incident on the system at an angle greater than about +30 degrees from the direction normal to the surface of the transparent composite.

Embodiment 9. The transparent composite of Embodiment 1, 2, 3, 4, 5, or 6, wherein the holographic element is configured to not diffract light incident on the system between the angles of about +30 degrees to -30 degrees from the direction normal to the surface of the transparent composite.

Embodiment 10. The transparent composite of Embodiment 1, 2, 3, 4, 5, or 6, wherein the holographic element is configured to not diffract visible light incident on the system at angles between about +15 degrees and about -15 degrees from the direction normal to the surface of the transparent composite.

Embodiment 11. The transparent composite of Embodiment 1, 2, 3, 4, 5, 6, 7, 8, 9, or

10, wherein the transparent composite has a transmittance in at least one viewing angle of at least 70% for wavelengths of light between about 400 nm and 700 nm.

Embodiment 12. The transparent composite of Embodiment 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, or 1 1, wherein the holographic element is optimized for different orientations of the solar array depending upon the position in the building or latitude of its location.

Embodiment 13. The transparent composite of Embodiment 1, 2, 3, 4, 5, 6, 7, 8, 9, 10,

11, or 12, wherein the holographic element comprises one or a multiplicity of materials. Embodiment 14. The transparent composite of Embodiment 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, or 13, wherein the holographic element comprises a photosensitive film.

Embodiment 15. The transparent composite of Embodiment 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, or 14, wherein the holographic element comprises dichromated gelatin, chemically modified dichromated gelatin, a photopolymer, a bleached or an unbleached photo emulsion, a nanoparticle doped photopolymer, a silver halide film, or a combination thereof.

Embodiment 16. The transparent composite of Embodiment 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, or 15, wherein the transparent substrate comprises a transparent glass or polymer material with a refractive index of between about 1.4 and about 1.7.

Embodiment 17. The transparent composite of Embodiment 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, or 16, wherein the transparent substrate comprises one or multiple transparent layers. Embodiment 18. The transparent composite of Embodiment 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, or 17, wherein more than one holographic element is present.

Embodiment 19. The transparent composite of Embodiment 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, or 18, wherein the holographic element is disposed on the transparent substrate.

Embodiment 20. The transparent composite of Embodiment 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, or 19, wherein the transparent substrate transparent matrix material comprises glass, a thiourethane, a polycarbonate (PC), allyl diglycol carbonate, a polyacrylate, an ester of a polyacrylic acid or a polyacrylic acid, 2-hydroxyethylmethacrylate, polyvinylpyrrolidinone, a hexafluoroacetone-tetrafluoroethylene-ethylene (HFA/TFE/E terpolymer), polymethyl methacrylate (PMMA), polyvinyl butyral (PVB), ethylene vinyl acetate, ethylene tetrafluoroethylene, a polyimide, polystyrene, a polyurethane, organosiloxane, a polyvinyl butyral-co-vinyl alcohol-co-vinyl acetate, a poly(ethylene teraphthalate) (PET), a cellulose triacetate TAC, acrylonitrite, a polybutadiene-modified polystyrene, a vinyl resin, polyethylene, polyvinyl chloride, polyvinyl acetate, polyvinyl alcohol, polyvinyl butyral, a cellulose derivative, an epoxy, or a polyester resin.

Embodiment 21. The transparent composite of Embodiment 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, or 20, wherein the transparent substrate comprises at least one layer comprising a host polymer, a host polymer and a co-polymer, or multiple polymers. Embodiment 22. The transparent composite of Embodiment 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, or 21, wherein the transparent substrate comprises a layer of a transparent inorganic amorphous glass.

Embodiment 23. The transparent composite of Embodiment 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, or 22, wherein the transparent substrate comprises a layer of a glass material comprising silicon dioxide, albite, crown, flint, low iron glass, borosilicate glass, soda-lime glass, or any combination thereof.

Embodiment 24. The transparent composite of Embodiment 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, or 23, further comprising a polymer layer, a glass layer, or a UV absorber material or layer.

Embodiment 25. The transparent composite of Embodiment 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, or 24, wherein the transparent substrate further comprises a luminescent material, wherein said luminescent material acts to absorb incident photons of a particular wavelength range, and re-emit those photons at a different wavelength, wherein a portion of the re-emitted photons are redirected into the building to improve illumination within the building.

Embodiment 26. The transparent composite of Embodiment 25, wherein the transparent substrate comprises a single layer, wherein said layer is a wavelength conversion layer, and wherein said wavelength conversion layer comprises a polymer matrix and a luminescent material.

Embodiment 27. The transparent composite of Embodiment 26, wherein the transparent substrate comprises two or more transparent layers, wherein at least one of the layers is a wavelength conversion layer, wherein said wavelength conversion layer comprises a polymer matrix and a luminescent material.

Embodiment 28. The transparent composite of Embodiment 25, 26, or 27, wherein the wavelength conversion layer or layers are sandwiched in between glass or polymer plates. Embodiment 29. The transparent composite of Embodiment 25, 26, 27, or 28, wherein the wavelength conversion layer or layers are on top of or on bottom of a glass or polymer plate.

Embodiment 30. The transparent composite of Embodiment 25, 26, 27, 28, or 29, wherein the transparent substrate comprises two or more luminescent materials.

Embodiment 31. The transparent composite of Embodiment 30, wherein the transparent substrate comprises two or more wavelength conversion layers, wherein each of the wavelength conversion layers independently comprises a different luminescent material such that each of the wavelength conversion layers absorbs photons at a different wavelength range.

Embodiment 32. The transparent composite of Embodiment 25, 26, 27, 28, 29, 30, or

31, wherein at least one of the luminescent materials is a down-shifting luminescent material. Embodiment 33. The transparent composite of Embodiment 25 to 32, wherein the luminescent material absorbs photons in the UV wavelength region, and re-emits the photons in the visible wavelength region.

Embodiment 34. The transparent composite of Embodiment 25, 26, 27, 28, 29, 30, 31,

32, or 33, wherein two or more luminescent materials absorb photons in the UV wavelength region.

Embodiment 35. The transparent composite of Embodiment 26, 27, 28, 29, 30, 31, 32,

33, or 34, wherein the polymer matrix of the wavelength conversion layer is formed from polyethylene terephthalate, polymethyl methacrylate, polyvinyl butyral, ethylene vinyl acetate, ethylene tetrafluoroethylene, polyimide, amorphous polycarbonate, polystyrene, siloxane sol-gel, polyurethane, polyacrylate, or a combination thereof.

Embodiment 36. The transparent composite of Embodiment 26, 27, 28, 29, 30, 31, 32, 33, 34, or 35, wherein the polymer matrix of the wavelength conversion layer comprises one host polymer, a host polymer and a co-polymer, or multiple polymers.

Embodiment 37. The transparent composite of Embodiment 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, or 36, wherein the refractive index of the polymer matrix material is in the range of about 1.4 to about 1.7.

Embodiment 38. The transparent composite of Embodiment 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, or 37, wherein the luminescent material is present in the polymer matrix in an amount in the range of about 0.01 wt% to about 3 wt%.

Embodiment 39. The transparent composite of Embodiment 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, or 38, wherein the luminescent material is a quantum dot material. Embodiment 40. The transparent composite of Embodiment 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, or 39, wherein the luminescent material is an organic compound. Embodiment 41. The transparent composite of Embodiment 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, or 40, wherein the luminescent material is a perylene derivative dye, a benzotriazole derivative dye, a diazaborinine, or a benzothiadiazole derivative dye. Embodiment 42. The transparent composite of Embodiment 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, or 41, wherein the luminescent material is represented by a structure of formula (I):

wherein Ri, R2, and R3 comprise and alkyl, a substituted alkyl, or an aryl.

Embodiment 43. The transparent composite of Embodiment 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, or 42, wherein the luminescent material is represented by a structure of formula (Il-a) or (Il-b):

(II-b);

wherein:

R is optionally substituted alkyl, optionally substituted alkenyl, optionally substituted cycloalkyl, optionally substituted heteroalkyl, optionally substituted aryl, optionally substituted heteroaryl, optionally substituted alkoxyalkyl, optionally substituted heteroalkenyl, optionally substituted arylalkyl, optionally substituted heteroaryl, optionally substituted cycloalkenyl, optionally substituted cycloheteroalkyl, optionally substituted cycloheteroalkenyl, optionally substituted amino, optionally substituted amido, optionally substituted cyclic amido, optionally substituted cyclic imido, optionally substituted alkoxy, optionally substituted carboxy, optionally substituted carbonyl, optionally substituted ether, optionally substituted ketone, optionally substituted sulfone, or optionally substituted sulfonamide; or R is an optionally substituted polycyclic ring system, wherein each ring is independently cycloalkyl, aryl, heterocycloalkyl, or heteroaryl;

R ⁴ , R ⁵ , and R ⁶ are independently optionally substituted alkyl, optionally substituted alkenyl, optionally substituted cycloalkyl, optionally substituted heteroalkyl, optionally substituted aryl, optionally substituted heteroaryl, optionally substituted alkoxyalkyl, optionally substituted heteroalkenyl, optionally substituted arylalkyl, optionally substituted heteroaryl, optionally substituted heteroarylalkyl, optionally substituted cycloalkenyl, optionally substituted cycloheteroalkyl, optionally substituted cycloheteroalkenyl, optionally substituted amino, optionally substituted amido, optionally substituted cyclic amido, optionally substituted cyclic imido, optionally substituted alkoxy, optionally substituted carboxy, optionally substituted carbonyl, optionally substituted ether, optionally substituted ketone, optionally substituted sulfone, or optionally substituted sulfonamide; or R ⁴ and R ⁵ , or R ⁴ and R ⁶ , or R ⁵ and R ⁶ , or R ⁴ and R ⁵ and R ⁶ , together form an optionally substituted ring or an optionally substituted polycyclic ring system, wherein each ring is independently cycloalkyl, aryl, heterocyclalkyl, or heteroaryl; and

L is of optionally substituted alkyl, optionally substituted heteroalkyl, optionally substituted alkylene, optionally substituted heteroalkylene, optionally substituted alkynylene, optionally substituted arylene, or optionally substituted heteroarylene.

Embodiment 44. The transparent composite of Embodiment 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, or 43, wherein the wavelength conversion layer further comprises a UV stabilizer, an antioxidant, or an absorber.

Embodiment 45. The transparent composite of Embodiment 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, or 44, wherein the thickness of the wavelength conversion layer is about 10 m to about 2 mm.

Embodiment 46. The transparent composite of Embodiment 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, or 45, wherein the system further comprises an additional polymer layer comprising a UV absorber.

Embodiment 47. The transparent composite of Embodiment 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, or 46, further comprising means for binding the holographic element, the transparent substrate, and any additional layer in the transparent composite.

Embodiment 48. The transparent composite of Embodiment 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, or 47, further comprising a photovoltaic cell.

Embodiment 49. The transparent composite of Embodiment 48, wherein the photovoltaic cell is attached to the edge surface of the transparent composite, and wherein the photovoltaic cell absorbs a portion of the light that is diffracted by the holographic optical element.

Embodiment 50. The transparent composite of Embodiment 42, 44, 45, 46, 47, 48, or 49, wherein the luminescent material comprises:

EXAMPLES

[0120] It has been discovered that embodiments of transparent composites described herein are useful for improving indoor illumination. These benefits are further shown by the following examples, which are intended to be illustrative of the embodiments of the disclosure, but are not intended to limit the scope or underlying principles in any way.

Example 1 - HOE/WLC

[0121] A glass substrate was cut to about 7" x 7" square. The cut glass sheet was cleaned with soap (washing detergent) and water, and then dried by nitrogen gas (N ₂ ) at room temperature.

Prepare Dichromate Gelatin (DCG) solution

[0122] In a light controlled (safe red light lamp) environment, 160 mL deionized (DI) water was added to 24 g of 300 bloom gelatin (Great Lakes Gelatin, Greyslake, IL, USA) and soaked for about 1 hour. The mixture was then stirred at about 50 °C until the gelatin was completely melted/dissolved (e.g., about 30 min). 8 g of ammonium dichromate(( H ₄ ) ₂ Cr0 ₄ ) was dissolved in about 40 mL DI water. This ( H ₄ ) ₂ Cr0 ₄ solution was added slowly to the gelatin solution and mixed for about 30 min at room temperature. The (NH ₄ ) ₂ Cr0 ₄ /gelatin mixture was filtered through a commercially available coffee filter paper. The filtered solution was kept in 50 °C water bath to prevent solidification.

Glass substrate coating

[0123] In a light controlled (safe red light lamp) environment, the cleaned and dried glass substrate sample was blown with 2 gas (room temperature for about 30 seconds) and heated to about 60 °C. The heated plate was spin coated with about 6 tablespoon filtered DCG solution at about 85 rpm for about 5 min. The coated glass substrate was then dried at about 50% humidity and about 20 °C for about 20 h. The thickness of the film was about 8 to 10 μιη. Recording of Hologram

[0124] The DCG-coated glass substrate was then cut into multiple 2" x 2" pieces. The DCG film was then exposed to two expanded and collimated (about 3" diameter) coherent 2W 532n laser beam (Coherent Verdi 5W) for about 45 seconds. The two laser beams incident from the same side of DCG film and has 50° and -50° to the DCG film normal. In this example, the incident laser beams were directly impinging the recording DCG film at the aforementioned angles (+ or - 50° to the DCG film normal), as opposed to using additional intervening prismatic elements to effect the desired incident angles. A hologram was formed by recording interferometric pattern on the DCG film based on the interference between the two laser beams.

Development of Transparent composite

[0125] After recording, the DCG film coated glass was detached from the mirror and was developed in Kodak Fixer™ solution for about 1 min and then rinsed about 20 min through a running DI water bath. While not wanting to be limited by theory, it is believed that rinsing the DCG film for about 20 min enables broad band (about 400 nm to about 700 nm) diffraction efficiency.

Synthesis of Chromophore Compounds (1013-21)

Intermediate A

[0126] Common Intermediate A was synthesized according to the following scheme.

Step 1 : 2-Isobutyl-2H-benzor<fllT .2.3 ^" |triazole.

[0127] A mixture of benzotriazole (11.91 g, 100 mmol), 1 -iodo-2-methylpropane (13.8 mL, 120 mmol), potassium carbonate (41.46 g, 300 mmol), and dimethylformamide (200 mL) was stirred and heated under argon at 40 °C for 2 d. The reaction mixture was poured into ice/water (1 L) and extracted with toluene/hexanes (2: 1, 2 x 500 mL). The extract was washed with IN HQ (2 x 200 mL) followed by brine (100 mL), dried over anhydrous magnesium sulfate, and the solvent was removed under reduced pressure. The residue was triturated with hexane (200 mL) and set aside at room temperature for 2 hours. The precipitate was separated and discarded, and the solution was filtered through a layer of silica gel (200 g). The silica gel was washed with hexane/dichloromethane/ethyl acetate (37:50:3, 2 L). The filtrate and washings were combined, and the solvent was removed under reduced pressure to give 2-isobutyl-2H-benzo[<i][l,2,3]triazole (8.81 g, 50% yield) as an oily product. ^X H NMR (400 MHz, CDC1 ₃ ): 57.86 (m, 2H, benzotriazole), 7.37 (m, 2H, benzotriazole), 4.53 (d, J = 7.3 Hz, 2H, j-Bu), 2.52 (m, 1H, j-Bu), 0.97 (d, J = 7.0 Hz, 6H, i- Bu).

Step 2: 4J-Dibromo-2-isobu -2H-benzor<iiri,2,3 ^" |triazole (Intermediate A).

[0128] A mixture of 2-isobutyl-2H-benzo[i/][l,2,3]triazole (8.80 g, 50 mmol), bromine (7.7 mL, 150 mmol) and 48% HBr (50 mL) was heated at 130 °C for 24 h under a reflux condenser connected with an HBr trap. The reaction mixture was poured into ice/water (200 mL), treated with 5 N NaOH (100 mL) and extracted with dichloromethane (2 x 200 mL). The extract was dried over anhydrous magnesium sulfate, and the solvent was removed under reduced pressure. A solution of the residue in hexane/dichloromethane (1 : 1, 200 mL) was filtered through a layer of silica gel and concentrated to give 4,7-dibromo-2- isobutyl-2H-benzo[< J[l,2,3]triazole, Intermediate A (11.14 g, 63% yield) as an oil that slowly solidified upon storage at room temperature. ^X H NMR (400 MHz, CDC1 ₃ ): δ 7.44 (s, 2H, benzotriazole), 4.58 (d, J = 7.3 Hz, 2H, j-Bu), 2.58 (m, 1H, j-Bu), 0.98 (d, J = 6.6 Hz, 6H, i- Bu).

Compound 1

[0129] Example Chromophore Compound 1 was synthesized according to the following reaction scheme.

4-/-BuOC ₆ H ₄ B(OH) ₂

A 1 [0130] A mixture of Intermediate A (1.32 g, 4.0 mmol), 4-isobutoxyphenylboronic acid (1.94 g, 10.0 mmol), tetrakis(triphenylphosphine)palladium(0) (1.00 g, 0.86 mmol), solution of sodium carbonate (2.12 g, 20 mmol) in water (15 mL), butanol (50 mL), and toluene (30 mL) was vigorously stirred and heated under argon at 100 °C for 16 hours. The reaction mixture was poured into water (300 mL), stirred for 30 min and extracted with toluene/ethyl acetate/hexane (5:3 :2, 500 mL). The volatiles were removed under reduced pressure, and the residue was chromatographed (silica gel, hexane/dichloromethane, 1 : 1). The separated product was recrystallized from ethanol to give pure 4,7-bis(4- isobutoxyphenyl)-2-isobutyl-2H-benzo[i/][l,2,3]triazole, Compound 1 (1.57 g, 83% yield). ¾ NMR (400 MHz, CDC1 ₃ ): 57.99 (d, J = 8.7 Hz, 4H, 4-/-BuOC ₆ H ₄ ), 7.55 (s, 2H, benzotriazole), 7.04 (d, J = 8.8 Hz, 4H, 4- -BuOC ₆ H ₄ ), 4.58 (d, J = 7.3 Hz, 2H, j-Bu), 3.79 (d, J = 6.6 Hz, 4H, 4-/-BuOC ₆ H ₄ ), 2.59 (m, 1H, j-Bu), 2.13 (m, 2H, 4- -BuOC ₆ H ₄ ), 1.04 (d, J = 6.6 Hz, 12H, 4-/-BuOC ₆ H ₄ ), 1.00 (d, J = 6.6 Hz, 6H, j-Bu). UV-vis spectrum (PVB): _mm = 359 nm. Fluorimetry (PVB): = 434 nm.

[0131] Mixing compound 1 with UV epoxy (NOA86H, Norland Products, Inc., Cranbury, NJ, USA): desired amount of compound 1 was added to NOA86H epoxy to make a total weight ratio of 0.5% compound 1 to epoxy. The mixture was mixed completely by excess amount of mechanical vibration. After mixing, the mixture was degassed by vacumm and ready to use. All the process was performed under red safe light in order to maintain the reactivity of the epoxy.

[0132] The HOE substrate was then, sequentially rinsed in IP A/water solutions (25/75, 50/50, 75/25, 90/10, and 100/0) for about 30 seconds for each bath. The film was then dried in an 80 °C chamber with a 2 gas flow of about 30 CFM for about 10 min. The dried film was then (removed) scratched about 2 mm about the entire perimeter of the film. A second 2" x 2" glass substrate, prepared as described earlier, was heated at about 85 °C for about 10 min. About 0.2 ml of compound 1 added UV curable epoxy was placed on the surface of the (dried film) second prepared glass substrate. The dried film was then deposited between the first and second glass substrates at room temperature with (until excess UV epoxy (and air bubbles) squeeze out any pressure/no heat) pressure and laminated. The laminated sample was then cured with about 10 mW/cm ² ultraviolet light (about 360 nm) (LOCKTITE®, Dusseldorf, Germany) for about 2 min.

[0133] Visible wavelength transmittance of the Example 1 - HOE film was measured by Shimadzu UV-3300 equipment. First, continuous spectrum light irradiated from a halogen lamp source at 150 W (MC2563, Otsuka Electronics, Inc., Osaka, Japan) with no sample in the sample holder was used to obtain air reference transmission data. Next, the sample (Example 1- HOE/WLC) was placed in the sample holder and irradiated with the same halogen lamp source. The transmitted spectrum was acquired for each sample by the multichannel photo detector. FIG. 7 shows the transmittance versus wavelength of the Example 1 - HOE/WLC film.

[0134] The diffraction efficiency of the HOE/WLC film was measured using an equation like below: A white light from Xenon source (Ocean Optics HL-2000-FHSA) was guided through a optic fiber, beam was collimated by confocal lens and incident onto HOE film from 50° from the normal of the film substrate. The passthrough light spectrum will be recorded by using fiber optical spectroscopy (StellaNets Black-Comet CXR-SR-50). The difference of the light spectrum with and without the HOE film will be used to decide the diffraction efficiency of HOE film at each wavelength as:

Diffraction Efficiency(wavelength)= I(with HOE/WLC)/I(without HOE/WLC)

[0135] FIG. 8 shows the diffraction efficiency of HOE film vs. different incident light wavelength.

Sunlight Redirection Measurement

[0136] The results of sunlight redirecting measurement of HOE/WLC film is shown at FIG. 9. The HOE/WLC film was placed at a holder and tilted about 50° towards the incident sunlight (from above hole). Both direct pass through light spot at the bottom and diffracted spot at the left as illustrated in FIG. 9.

[0137] As shown in FIG. 7, the HOE/WLC show excellent transparency (>85%) between 400-700 nm when viewed from 0° from the surface normal. On the other hand, sunlight coming from a different incident angle (50°), after passing through the HOE/WLC film, as shown in FIG.8, a relatively flat diffraction efficiency performance across the 400-700 nm visible wavelength was observed. This will ensure redirection of the entire white spectrum of the sunlight. As illustrated at FIG. 9, part of the incident sunlight can be diffracted out of the original path by HOE/WLC film and can be potentially useful for indoor illumination. [0138] Unless otherwise indicated, all numbers expressing quantities of ingredients, properties such as molecular weight, reaction conditions, and so forth used in the specification and claims are to be understood as being modified in all instances by the term "about." Accordingly, unless indicated to the contrary, the numerical parameters set forth in the specification and attached claims are approximations that may vary depending upon the desired properties sought to be obtained. At the very least, and not as an attempt to limit the application of the doctrine of equivalents to the scope of the claims, each numerical parameter should at least be construed in light of the number of reported significant digits and by applying ordinary rounding techniques.

[0139] The terms "a," "an," "the" and similar referents used 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. 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 any claim. No language in the specification should be construed as indicating any non- claimed element essential to the practice of the invention.

[0140] Groupings of alternative elements or embodiments disclosed herein are not to be construed as limitations. Each group member may be referred to and claimed individually or in any combination with other members of the group or other elements found herein. It is anticipated that one or more members of a group may be included in, or deleted from, a group for reasons of convenience. When any such inclusion or deletion occurs, the specification is deemed to contain the group as modified thus fulfilling the written description of all Markush groups used in the appended claims.

[0141] Certain embodiments are described herein, including the best mode known to the inventors for carrying out the invention. Of course, variations on these described embodiments will become apparent to those of ordinary skill in the art upon reading the foregoing description. The inventor expects skilled artisans to employ such variations as appropriate, and the inventors intend for the invention to be practiced otherwise than specifically described herein. Accordingly, the claims include all modifications and equivalents of the subject matter recited in the claims as permitted by applicable law. Moreover, any combination of the above-described elements in all possible variations thereof is contemplated unless otherwise indicated herein or otherwise clearly contradicted by context.

[0142] In closing, it is to be understood that the embodiments disclosed herein are illustrative of the principles of the claims. Other modifications that may be employed are within the scope of the claims. Thus, by way of example, but not of limitation, alternative embodiments may be utilized in accordance with the teachings herein. Accordingly, the claims are not limited to embodiments precisely as shown and described.