IR REFLECTIVE FILM

Abstract

A translucent or transparent film or sheet device shows angular-independent IR reflectance, which comprises a substrate (1) covered with a layer of a dielectric high refractive index material (4) containing a thin metallic layer (3) embedded in said material, and a further layer (5) of translucent or transparent material covering said layer (4) of dielectric high refractive index material, characterized in that the embedded metal layer (3) is periodically interrupted with a periodicity of 50 to 800 nm such that metal covers at least 70% of the substrate area. The device may advantageously be integrated into a window, a glass facade element or especially onto a photovoltaic (PV) device, where it reduces the fraction of IR radiation passing into the building, or reduces heat take-up and thus lowers the operating temperature and improves the efficiency of the PV cell.

Claims

1.-16. (canceled)

17. A translucent or transparent film or sheet comprising a substrate (1) covered with a layer of a dielectric high refractive index material (4) containing a thin metallic layer (3) embedded in said material, and a further layer (5) of translucent or transparent material covering said layer (4) of dielectric high refractive index material, characterized in that the embedded metal layer (3) is periodically interrupted with a periodicity of 50 to 800 nm such that metal covers at least 70% of the substrate area.

18. The film or sheet of claim 17, wherein the refractive index of the high refractive index material is higher than 1.9.

19. The film or sheet of claim 17, wherein the periodicity of interruptions in the metal layer (3) within at least one dimension is from the range 100 to 500 nm, or the embedded metal layer covers 70 to 99% of the substrate area.

20. The film or sheet according to claim 17, wherein the thickness of the metal layer (3), perpendicular to the substrate plane, is from the range 4 to 20 nm, or the thickness of the layer of dielectric high refractive index material (4) is 20 to 50 nm on each side of the metal layer.

21. The film or sheet according to claim 17, wherein the metal layer consists essentially of silver, aluminum, copper, or gold.

22. The film or sheet according to claim 17, wherein the high refractive index material is selected from the group consisting of metal chalcogenides and metal nitrides.

23. The film or sheet according to claim 17, further comprising an antireflex coating (2) on top of the further layer (5).

24. The film or sheet according to claim 23, wherein adjacent layers (1), (3), (4), (5) and optionally (2) each are in direct optical contact with each other.

25. A window, glass facade element or solar panel comprising the film or sheet according to claim 17.

26. The window, glass facade element, or solar panel claim 25, wherein the window, glass façade element, or solar panel is a solar panel, and wherein the film or sheet is positioned as a cover film of photovoltaic cells comprised in said solar panel.

27. A method for manufacturing the translucent or transparent film or sheet according to claim 17, which method comprises a) structuring at least one surface of a suitable film or sheet substrate (1) to obtain grooves or ditches with a periodicity from the range 50 to 800 nm and a width of about 4 to about 10 percent of the periodic, and a depth from the range 5 to 100 nm; b) depositing a layer of high refractive index material onto at least one structured surface thus obtained; c) depositing a thin metallic layer by thermal evaporation or physical vapor deposition, optionally under an oblique angle, onto the surface obtained in step (b), thus obtaining interruptions in the metallic layer which are at least partially located at the grooves or ditches introduced in step (a); d) depositing another layer of high refractive index material onto said interrupted metallic layer of step (c); e) covering the layer of high refractive index material obtained in step (d) with one or more layers of a translucent or transparent dielectric material; and optionally f) depositing an antireflex layer onto the surface obtained in step (e).

28. A method for manufacturing a translucent or transparent film or sheet according to claim 17, which method comprises a) providing a suitable film or sheet substrate (1); b) depositing a layer of high refractive index material onto at least one surface of said substrate; c) depositing a thin metallic layer onto the surface obtained in step (b); d) introducing interruptions into the metallic layer by removal of 1 to 30% of the metallic layer area with a periodicity from the range 50 to 800 nm while retaining 70 to 99% of the metallic layer area essentially unmodified, for example by plasma etching, embossing, cutting or punching; e) depositing another layer of high refractive index material onto said interrupted metallic layer of step (d); f) covering the layer of high refractive index material obtained in step (e) with one or more layers of a translucent or transparent dielectric material; and optionally g) depositing an antireflex layer onto the surface obtained in step (f).

29. The film or sheet according to claim 17, wherein the substrate (1) and/or the further layer (5) are polymeric materials or glass.

30. The window pane, glass facade element or solar panel of claim 25, wherein the substrate comprises a flat or bent polymer film or sheet, or glass sheet, or a polymer film or sheet and a glass sheet.

31. A method for reducing the transmission of solar IR radiation from the range 700 to 1200 nm, through a transparent element such as a polymer film, plastic screen, plastic sheet, plastic plate, glass screen, especially of a window, architectural glass element or solar panel, which method comprises integrating film or sheet according to claim 17 into said transparent element.

32. A method for reducing entry of IR radiation through a window or glass façade element into interior space of a building, or for reducing heat uptake of a solar panel or photovoltaic cell, comprising incorporating the film or sheet according to claim 17 into said window or glass façade element or solar panel or photovoltaic cell.

Description

EXAMPLES

Example 1: Protection Foil Containing Silver on ZnS Grating

[0113] The following materials are chosen:

TABLE-US-00001 metal silver high index refraction material ZnS substrate PMMA film, thickness 125 micrometer passivation layer UV cured Lumogen ® OVD 301
single layer antireflex (AR) coating low refractive index SiO2 nanoparticle coating The AR coating is as described by Wicht et al., Macromolecular Materials and Engineering 295, 628 (2010), using 1.3 g of SiO2 nanoparticles of 8 nm primary particle size and 0.3 g of polyvinyl alcohol on 35 ml water and 0.01 g of sodium tetraborate.

[0114] The geometry of the AR and the metal/high index of refraction layers are;

TABLE-US-00002 AR layer thickness 115 nm refractive index of AR layer 1.22 silver layer thickness 9 nm (horizontal and vertical part) silver grating period 240 nm duty cycle (DC) 0.9 ZnS thickness 35 nm each (underneath and above silver layer) passivation layer thickness  5 μm

[0115] The thickness of the passivation layer is typically from the range 5 μm or more, thus having no significant impact on the optical properties of the protection foil. The profile of the resulting protective foil is shown in FIG. 1.

[0116] The device shown in FIG. 1 is obtained as shown in FIG. 8:

i) a 125 micrometer PMMA film is hot embossed (line grating of period 240 nm, depth 9 nm, trench width 24 nm);
ii) a thin layer of zinc sulphide (ZnS 35 nm) is coated onto the patterned substrate (Baizers BAE 250, coating perpendicular to the substrate);
iii) the patterned ZnS layer thus obtained is then coated on the top areas and one side area of the grating with a silver layer using physical vapour deposition of silver from the side using a thermal evaporator vacuum chamber. The silver thickness selected is 9 nm on top and side, evaporation angle is 50°, such that only a part of the grating is metalized;
iv) another layer of ZnS (35 nm, Balzers BAF 250) is deposited, also filling the trenches not coated in step iii), thus isolating the silver coated areas from each other;
v) the patterned and coated substrate thus obtained is passivated with Lumogen® OVD 301 abd UV cured (dry film thickness 5 micrometer); and
vi) an AR film of composition described above is coated onto the passivation layer.

[0117] Based on the above material and geometrical data, the transmission and reflection of the protective optical foil is simulated under the assumption, that the substrate is semi-infinite such that no reflections occur at the lower substrate interface (opposite to the AR layer). The transmission and reflection for perpendicular incident light (θ=0°) is shown in FIG. 2. The transmission and reflection for an incident light (θ=60°) is shown in FIG. 3. The plane of incident light is perpendicular to the grating orientation.

[0118] From the simulated photo-spectra, the light transmittance τ.sub.v according to the European standard DIN EN 410 or (equivalently) the international standard ISO 9050, and reflection R (at 1.95 micrometer, i.e. the approx. maximum of the infrared reflection) are extracted and summarized in Table 1.

TABLE-US-00003 TABLE 1 extracted transmittance τ.sub.v and reflection in the infrared from the simulated transmission and reflection spectra incidence angle θ τ.sub.v R(1.95 μm)  0° 96% 83% 60° 90% 80%

[0119] From FIG. 2, FIG. 3 and Table 1 it is seen that the metallic grating with the ZnS layers and the AR coating on top of the protection foil results in a high visible transmittance τ.sub.v(0°) of 96% and a maximal reflection of 83% at 1.95 μm in the infrared, while showing a weak angular dependence.

Example 2 (Comparison): Non Patterned (Continuous) Silver Layer

[0120] For the purpose of comparison, a simulation as described in example 1 is also carried out for a protective device with a non-patterned thin silver layer. The cross-section of the device is shown in FIG. 4; silver thickness of 9 nm, each ZnS layer of thickness of 35 nm, substrate, passivation layer and AR layer are as in example 1. The transmission and reflection spectra are shown in FIG. 5 (θ=0°) and FIG. 6 (θ=60°). From the simulated photo-spectra, the transmittance and reflection R (at 1.95 micrometer, i.e. the approx. maximum of the infrared reflection) in the infrared are extracted and summarized in Table 2.

TABLE-US-00004 TABLE 2 extracted transmittance τ.sub.v and reflection in the infrared from the simulated transmission and reflection spectra for the device with the non-patterned silver layer incidence angle θ τ.sub.v R(1.95 μm)  0° 98% 72% 60° 94% 70%

[0121] The protective foil based on the non-patterned silver film shows a slightly higher transmittance (difference: 2% at 0° and 4% at 60°) and a distinctly lower infrared reflection (difference: 11% at 0° and 10% at 60°) compared to the same device comprising the interrupted silver layer according to the present invention.

Example 3: Protection Foil Containing Interrupted Flat Silver Layer Embedded in ZnS Layer

[0122] An additional example of a protective foil based on a patterned metal is shown in FIG. 7.

Example 4

[0123] FIG. 9 shows a further approach to fabricate the described optical device. Instead of embossing wells (FIG. 8), elevations are embossed. The first HRI coating (FIG. 9 b) may be preferable over the approach illustrated by FIG. 8 (b). Again, interruptions in the metallic layer are obtained as an effect of the grating shadow during metallization under oblique angle.

Example 5: Fabrication of a Device by Perpendicular Coatings and Nano-Cutting

[0124] In the method shown in FIG. 10, interruptions in the metallic layer are obtained by cutting. The substrate is subsequently coated with the HRI material and the metal layer. Then, the metal layer and, in part, the underlying HRI layer is cut using a nano-cutting tool. Finally the device is coated with another layer of HRI material and a passivation material.

[0125] The step of nano-cutting is carried out in analogy to the method described by N. Stutzmann et. al., Advanced Functional Materials 12, 105 (2003).

[0126] An optical simulation of the device based on the patterned layers shown in FIG. 10 is carried out using the following parameters:

TABLE-US-00005 period 240 nm silver thickness  9 nm duty cycle 0.95 HRI material ZnS thickness ZnS (each layer)  35 nm substrate, superstrate PMMA thicknesses substrate, superstrate semi-infinite light of incidence angle 0° (perpendicular to device)

[0127] The simulated transmission and reflection spectra are shown in FIG. 12. The resulting τ.sub.v=97% and the reflection R(1.95 μm)=82%.

Example 6: Fabrication of a Device by Nano-Embossing and by Perpendicular Coatings

[0128] FIG. 11 shows a further approach to fabricate described optical devices. Here again, trenches are embossed and the HRI material is coated perpendicular to the substrate. In the next steps, a metal and a second HRI layer are subsequently coated perpendicular to the substrate. Finally the device is passivated with a UV cross-linkable material.

[0129] In this approach, the metal layer is interrupted at two locations per period and results in two metal layers a major raised metal area and a minor lowered metal area. The metal coverage (duty cycle) is defined by the ratio of the major metal area to the total area, the metal layer (major and minor) thus covers the total coated area, the duty cycle thus being 100%.

[0130] After the device fabrication, an antireflective coating for the visible wavelength range is advantageously applied to the top of the device.

[0131] Optical simulations of the device based on the patterned layers shown in FIG. 11 are carried out using the following parameters:

TABLE-US-00006 grating period 240 nm grating depth 26 nm (distance between major and minor metal areas) silver thickness  9 nm fraction of elevated metal layer (DC') 0.95 HRI material ZnS thickness ZnS  35 nm substrate, superstrate PMMA thicknesses substrate, superstrate semi-infinite light of incidence angle 0° (perpendicular to device)

[0132] The simulated transmission and reflection spectra are shown in FIG. 13. The resulting τ.sub.v=97% and the reflection R(1.95 μm)=81%.

BRIEF DESCRIPTION OF FIGURES

[0133] FIG. 1 Cross-section through the protective foil, which contains [0134] 1: foil substrate [0135] 2: AR coating [0136] 3: patterned metal layer (thickness d; duty cycle=DC/P) [0137] 4: high index of refraction layer above and underneath the metal layer [0138] 5: passivation or spacer layer between the upper high index of refraction layer and the AR coating.

[0139] FIG. 2 Simulated transmission and reflection spectra for θ=0°.

[0140] FIG. 3 Simulated transmission and reflection spectra for θ=60°.

[0141] FIG. 4 Cross-section through the protective foil based on an non-patterned metal layer, which contains [0142] 1: foil substrate [0143] 2: AR coating [0144] 3: thin metal layer of thickness d [0145] 4: high index of refraction layer above and underneath the metal layer [0146] 5: passivation or spacer layer between the upper high index of refraction layer and the AR coating.

[0147] FIG. 5 Simulated transmission and reflection spectra for θ=0° for the non-patterned metal layer.

[0148] FIG. 6 Simulated transmission and reflection spectra for θ=60° for the non-patterned metal layer.

[0149] FIG. 7 Cross-section through the additional protective foil based on a patterned metal layer, parameter as defined in FIG. 1.

[0150] FIG. 8 Fabrication of a device as shown in FIG. 1; a) substrate is hot- or UV-embossed, b) a thin layer of HRI material is coated onto the patterned substrate (coating perpendicular to the substrate); c) a thin layer of metal is coated obliquely; d) a thin layer of HRI material is coated onto the patterned substrate (coating perpendicular to the substrate); e) the patterned and coated substrate is passivated with a dielectric material; f) antireflex film on top of the patterned, coated and passivated foil.

[0151] FIG. 9 Alternative fabrication of a device: a) substrate is hot- or UV-embossed, b) a thin layer of HRI material is coated onto the patterned substrate (coating perpendicular to the substrate); c) a thin layer of metal is coated obliquely; d) a thin layer of HRI material is coated onto the patterned substrate (coating perpendicular to the substrate); e) the patterned and coated substrate is passivated with a dielectric material.

[0152] FIG. 10 Fabrication of a device by nano-cutting: a) the substrate is coated with a layer of HRI material; b) a thin layer of metal is coated onto the HRI layer (coating typically perpendicular to the substrate, no oblique angle required); c) with a cutting tool holding the required period, the coated substrate is embossed such that the metal layer gets patterned with thin slits d) a thin layer of HRI material is coated onto the patterned substrate (coating perpendicular to the substrate); e) the patterned and coated substrate is passivated with a dielectric material.

[0153] FIG. 11 Fabrication of a device by embossing followed by conventional PVD: [0154] a) the substrate is hot- or UV-embossed, depth typically larger than intended thickness of metal layer, and less than intended thickness of HRI layer; [0155] b) the thin layer of HRI material is coated onto the patterned substrate (coating perpendicular to the substrate); [0156] c) the thin layer of metal is coated perpendicular to the substrate; [0157] d) the 2nd thin layer of HRI material is coated onto the patterned substrate (coating perpendicular to the substrate); [0158] e) the patterned and coated substrate is passivated with dielectric material.

[0159] FIG. 12 Simulated transmission and reflection spectra based on patterned layers as shown in FIG. 10.

[0160] FIG. 13 Simulated transmission and reflection spectra based on patterned layers as shown in FIG. 11.