A visibly transparent coating and a transparent sheet

Abstract

A visibly transparent sheet (200) and a coating for a transparent substrate (201), the coating comprising: - a first film comprising: a first stacked layer mirror film configured to reflect light in an infrared range of light and to transmit light in a visible range of light, or a first transparent conductive oxide film, - a set of structures (112) arranged in a pattern on the first film, separated by recesses (111) comprising one or more empty first unit cells (111a), each structure comprising one or more second unit cells (112a), the first and second unit cells having identical shapes and sizes, - wherein each second unit cell comprises a second layer structure comprising: a second stacked layer structure comprising at least a third dielectric layer, a fourth dielectric layer, and a second metal layer arranged between the third and fourth dielectric layers, or a second transparent conductive oxide layer. An active coating incorporating switchable materials is also proposed, enabling dynamic control over various properties. This coating facilitates the modulation of infrared transmission, reflection, or absorption of solar light in response to changing ambient conditions.

Description

[0001] A VISIBLY TRANSPARENT COATING AND A TRANSPARENT SHEET

[0002] TECHNICAL FIELD

[0003] The present invention relates to a visibly transparent coating for a transparent sheet such as a glass sheet. It further relates to a transparent sheet and to a window.

[0004] The invention may be applied in facades or roofs, windows, doors, or other transparent surfaces in buildings, vehicles, greenhouses, goggles, etc.

[0005] BACKGROUND OF THE INVENTION

[0006] Windows substantially reduce the energy efficiency of buildings and homes, especially in cold climates. They are thermal escape routes from a warmer indoors climate, and the window glazing is typically at a few degrees below room temperature. As a result of indoors comfort requirements, increased energy consumption for heating is needed, often by thermal radiators located under the windows. In EU households alone, heating and hot water account for 79% of total energy consumption. At the same time, 75% of heating and cooling in the EU is still generated by fossil fuels.

[0007] Low-emissivity (Low-E) glasses exist that comprise a visibly transparent coating that reflect a certain amount of radiation outside of the visible spectrum, i.e., light within the infrared (IR) parts of the spectrum, without minimizing the amount of visible (vis) light that passes through. The Low-E coatings are hence designed to keep the indoors temperature consistent by reflecting the infrared radiation, preventing heat from escaping. Typical Low- E glass reflects a certain amount of infrared (IR) and ultraviolet (UV) light without minimizing the amount of visible (vis) light that passes through. Low-E glass windows have a thin coating of several hundreds of nanometers (nm) thick. The typical Low-E coatings are based on transparent conductive oxide (TCO) or an Ag thin film-stack layer. They are often fabricated as thin films of about 300 nm thickness in order to show high transparency, such as about 85%, in the visible range and high reflectance at long wavelengths, such as about 70% in the near-IR range and about 98% in the mid- and far- IR ranges. All available Low-E coatings possess specular reflection of electromagnetic radiation and are non-transparent for long wavelengths. This means that mobile networks microwave signals are also reflected by the commercially available Low-E glasses.

[0008] Conventional Low-E glasses are also associated with other drawbacks, such as: the glass reflects some color, so it is not 100% clear / color neutral in appearance, causing the impression of a dirty / contaminated surface; it damages the plastic windows siding, causing warping and even melting because of the specularly reflected thermal solar light that substantially heats the environment and the direct surroundings of the window; it destroys green plants near such windows, or in the yard / lawn directly in front of such windows, because of the highly-efficient specular reflection of the thermal solar radiation, directing it to the greenery / soil beneath the window.

[0009] In view of the above, there is a strive to develop better coatings for windowpanes and other transparent surfaces used in buildings, vehicles, and similar applications, that avoid near-IR specular reflection and preserve heat indoors without blocking microwave signals.

[0010] SUMMARY OF THE INVENTION

[0011] A first object of the present invention is to provide a visibly transparent coating for a transparent substrate and a visibly transparent substrate that overcomes or at least alleviates the problems associated with conventional Low-E coatings and glasses.

[0012] Another object is to provide an active coating incorporating switchable materials, enabling dynamic control over various properties of the coating so as to facilitate the modulation of infrared transmission, reflection, or absorption of solar light in response to changing ambient conditions.

[0013] According to a first aspect of the invention, at least the first object is achieved by a visibly transparent coating according to claim 1. Hence, a visibly transparent coating for a transparent substrate such as a transparent glass substrate, e.g., a glass sheet, is provided. The coating is configured to be provided on a surface of the glass substrate and comprises: a first film comprising one of: a first stacked layer mirror film comprising at least a first dielectric layer, a second dielectric layer, and a first metal layer arranged between the first and second dielectric layers, the first stacked layer mirror film being configured to reflect light in an infrared, I R, range of light and to transmit light in a visible range of light, and a first transparent conductive oxide film, at least one set of structures arranged in a pattern on a top surface of the first film, the structures being separated by recesses comprising one or more empty first unit cells, each structure within the at least one set of structures comprising one or more second unit cells, the first and second unit cells having identical shapes and sizes as measured in a plane parallel with the top surface of the first film, wherein each one of the second unit cells comprise at least a second layer structure comprising one of: a second stacked layer structure comprising at least a third dielectric layer, a fourth dielectric layer, and a second metal layer arranged between the third and fourth dielectric layers, and a second transparent conductive oxide layer.

[0014] The present invention uses functional transparent surfaces that rely on renewable energy sources in the form of solar light and the interplay of various energy systems like solarbased thermal energy generation and thermal isolation with diffuse scattering of IR light for interior heating in buildings and heat loss reduction, and IR absorption for industryscale thermal energy production and collection. The functional transparent surfaces work with both optical (UV, visible, near-infrared) and thermal solar photons, and can be developed as a part of the facade / roof, windows and doors or other transparent surfaces in vehicles, greenhouses, goggles, etc., with passive, i.e. , with zero energy consumption, and active, i.e., changing the thermal / optical properties with an applied external small electrical bias, thermal management technology.

[0015] Thanks to the pattern comprising structures and recesses formed by unit cells, specular reflection of IR light is avoided. This is achieved since the first and second unit cells have out-of-phase optical responses. The first and second unit cells hence reflect near-infrared light at different phases such that the light reflects in all directions instead of in only one specular direction. Diffuse scattering, i.e., omnidirectional reflection, of incident IR radiation can thereby be achieved. This reduces problems with strong local heating around windows provided with the coating.

[0016] According to the first aspect of the invention, the first film acts as a mirror for IR radiation, while the structures arranged on top thereof adjust the properties of the coating. Benefits of using structures-on-mirror instead of Low-E glass include: diffuse scattering / reflection to avoid direct heating of the surroundings of the window by the specularly-reflected IR solar radiation;

[0017] 100% colour rendering, i.e., no colour change in the visible spectrum since the structures are selectively resonant outside of the visible spectral range and also due to using only colourless visibly materials or a very small amount of metal, making the material light absorption in metals negligible; a possibility to manipulate the scattered / reflected light in a specific direction by proper adjustment of the structure design, including multibeam scattering, reflect- array, retro-reflector; spectral selectivity of structures gives freedom in choosing of blocking / reflecting specific wavelength bands of solar light; full transparency to the microwave I mobile signal radiation when the size and thickness of structures are made significantly smaller than the wavelengths in the microwave spectral range.

[0018] A material layer used to form the structures has been patterned using, e.g. various types of bottom-up or top-down lithographies in combination with materials depositions and / or various etching techniques, including hole-mask lithography, block-copolymer lithography, e-beam lithography, direct laser writing, photolithography, imprint lithography and others; reactive ion and other types of directional or non-directional etching; e-beam deposition, sputtering, chemical or vapor growth.

[0019] Each structure comprises one second unit cell, or two or more second unit cells being adjacent to one another. Each recess comprises one first unit cell, or two or more first unit cells being adjacent to one another. The first and second unit cells may be shaped such that they together cover the entire surface without overlaps. A structure is to be understood as a continuous shape comprising one or more second unit cells, wherein each two neighbouring second unit cells within a structure are in edge-to-edge contact. For example, when square second unit cells are provided, a structure formed by two neighbouring second unit cells is in the form of a rectangle. Two second unit cells sharing only a corner are herein not considered as being part of the same structure, unless being connected by other second unit cells. Similarly, a recess is to be understood as a continuous space comprising one or more first unit cells, wherein each two neighbouring first unit cells within a recess are in edge-to-edge contact.

[0020] Optionally, each one of the first and second unit cells has an area of 4-400 pm2, preferably 20-300 pm2, as measured in said plane parallel with the top surface of the first film.

[0021] Optionally, each one of the first and second unit cells has a square shape with a side length of 2-20 pm, preferably 3-10 pm, as measured in said plane. When the unit cells are square, the structures and recesses are, as seen in the plane, in the form of polyominos. Square unit cells provide a large versatility, symmetry, and a relatively easy fabrication.

[0022] Hence, the sizes of the structures are significantly smaller than the wavelength of the mobile network radiation signal. The structures are thereby invisible to the mobile network signal. Their specific scattering / reflection resonances are hereby tuned to be completely outside of the mobile signal range.

[0023] As an alternative to square unit cells, triangle or hexagonal unit cells may be used.

[0024] Optionally, the pattern is formed by using an optimization algorithm that combines the first and second unit cells to minimize specular reflection of near-infrared light. Algorithms that may be used to form the pattern to minimize specular reflection and achieve a uniform backward scattering pattern include genetic algorithms1, particle swarm optimization2, combinatorial optimization techniques3, and other suitable optimization methods.

[0025] Optionally, the at least one set of structures covers 30-70% of the first film, preferably 40- 60%.

[0026] 1Holland, J. H. (1992). Genetic algorithms. Scientific American, 267(1), 66-73.

[0027] 2Kennedy, James, and Russell Eberhart. "Particle swarm optimization." In Proceedings of ICNN'95- international conference on neural networks, vol. 4, pp. 1942-1948. IEEE, 1995.

[0028] 3Grotschel, M., Lovasz, L., & Schrijver, A. (2012). Geometric algorithms and combinatorial optimization (Vol. 2). Springer Science & Business Media. Optionally, the structures have a height of 0.05-1 pm, preferably 0.1-0.8 pm, more preferably 0.1-0.4 pm, as measured in a direction perpendicular to said plane.

[0029] Optionally, the visibly transparent coating is configured for diffuse, i.e. , omnidirectional, scattering of light within the infrared range of light, including the near-infrared range. For this purpose, the structures comprise the second stacked layer structure, wherein the second metal layer is a noble metal layer, preferably a silver layer, a gold layer, or a copper layer, most preferably a silver layer. Alternatively, the structures may comprise the second transparent conductive oxide layer. The first film may be either the first stacked layer mirror film, or the first transparent conductive oxide thin film, with or without a dielectric spacer layer provided between the first transparent conductive oxide thin film and the structures.

[0030] Optionally, the first stacked layer mirror film further comprises a first intermediate layer sandwiched between the first metal layer and the first dielectric layer, and / or a second intermediate layer sandwiched between the first metal layer and the second dielectric layer. The first stacked layer mirror film may be a five-layer mirror film. The intermediate layer(s) may serve to promote crystal growth of metal grains within the first metal layer, thereby improving optical properties of the coating. The intermediate layer(s) may, e.g., comprise ZnO, TiO2, or other semiconductor materials that may promote grain growth in the metal layer.

[0031] Optionally, the second stacked layer structure further comprises a third intermediate layer sandwiched between the second metal layer and the third dielectric layer, and / or a fourth intermediate layer sandwiched between the second metal layer and the fourth dielectric layer. The second stacked layer structure may be a five-layer mirror structure. The intermediate layer(s) may serve to promote crystal growth of metal grains within the second metal layer, thereby improving optical properties of the coating. The intermediate layer(s) may, e.g., comprise ZnO, TiO2, or other semiconductor materials that may promote grain growth in the metal layer. The second stacked layer structure may have the same configuration, in terms of layers and materials, as the first stacked layer mirror film.

[0032] Optionally, the second unit cells further comprise at least one phase-change material layer or a liquid crystal elastomer layer. Optionally, the coating further comprises a third film arranged between the first film and the at least one set of structures, wherein the third film comprises a phase-change material layer or a liquid crystal elastomer (LCE) layer. The phase-change material will change its refractive index as a result of the phase transition, thereby changing its response to incident light. The LCE layer will change thickness as a function of temperature rather than experiencing a phase transition. Instead of a change in refractive index, the thickness change leads to a change in the degree of coupling and in the interference of light, constructive or destructive, when scattered / reflected between the structures and the first film, acting as a mirror.

[0033] The use of a phase-change material layer or an LCE layer within the structures and / or between the first film and the at least one set of structures enables the creation of a coating with active control / switching of absorption vs. diffuse reflection / scattering of solar light in the infrared range while keeping the coating and the coated sheet close to 80-90% transparent in the visible wavelength range. The combination of these two functionalities with active control, for example, in windows, allows a reduction in energy consumption and a comfortable indoor environment. It enables the creation of visibly transparent active thermal surfaces, marking the way to active windows drastically reducing the overall energy consumption of buildings, reducing the energy needed for cooling in greenhouses in hot climates, or control de-fogging and de-icing of other transparent surfaces like automotive windshields and similar.

[0034] Optionally, the first film is the first triple-layer mirror film, the second unit cells comprise the second triple-layer structure, and the phase-change material layer is sandwiched between the second dielectric layer and the third dielectric layer.

[0035] Optionally, the at least one phase-change material layer comprises a thermally or electrically switchable phase-change material having a transition temperature above which it is metallic and below which it is dielectric or semi-conducting.

[0036] By embedding dielectric-to-metal phase transition material like vanadium dioxide (VO2) inside the structures, for example, as a spacer between two elements in a vertical stack, the IR transmission / reflection or absorption of solar light can be dynamically autonomously changed in response to ambient conditions. In general, it is very challenging to achieve window retrofits that are simultaneously thermally insulating, visible-light transparent, and dynamically switchable in IR solar transmission or absorption. However, thermally switchable phase-change materials, also referred to as thermochromic materials, can assist with this. Such materials are of great interest as they can dynamically modulate solar transmission, in the visible and infrared ranges, by up to about 60% when the environment changes. Compared with electrochromic, thermochromic windows are more attractive due to their unique characteristics, including low cost and automatic response to temperature change. VO2 has demonstrated a promising regulation ability of solar transmission in the near-infrared range, 780-2500 nm wavelength, through a reversible insulator / semiconductor-metal phase transition at 68°C. By doping with other elements such as magnesium or tungsten, the phase transition temperature of doped VO2 can be tailored down to room temperature. This offers a unique ability to manipulate the IR spectrum of sunlight using VC>2-containing structures.

[0037] Optionally, the at least one phase-change material layer comprises an electrically switchable phase-change material, exhibiting an amorphous-to-crystalline phase transition as an external voltage is applied. Such phase-change materials are not temperaturedependent and instead reversibly transforms from the amorphous to crystalline phase by a short electric pulse of low voltage, such as about 2.5 V. Materials that may be used include GeSbTe, i.e., germanium-antimony-tellurium (GST), InSb, GeTe, GeSb2Te4, Ge2Sb2Tes (GST), AglnTe2, InSb, and similar true phase-change materials. An advantage in comparison to thermally switchable phase-change materials is that only a short electric pulse of low voltage is needed.

[0038] In this case, the coating may further comprise a conductive layer arranged between the at least one set of structures and the first film, such as a visibly transparent metal grid. The metal grid may be an ordered I square grid produced by lithography or a disordered grid formed by crossed metal nanowires, synthesised and dropped on the surface from solution to form the grid. The crossed metal nanowires may have a diameter of 0.2-5 pm.

[0039] Optionally, the coating is a discontinuous coating in the form of an array of patches configured to be provided on the surface of the transparent substrate, each two adjacent patches being separated by a gap, each patch comprising said at least one set of structures separated by said recesses. The array of patches thus forms a metasurface covering the substrate on which the coating is provided. The gap between the patches may be a non-coated gap. By providing the coating in the form of a discontinuous coating comprising an array of patches, a frequency-selective surface can be achieved that can selectively control the transmission and reflection of electromagnetic waves based on their frequency. The proposed frequency-selective surface is tuned to block mid-infrared wavelengths of electromagnetic radiation while allowing radio frequencies to pass through.

[0040] Optionally, the patches are identical and form a repeating pattern on the surface of the transparent substrate.

[0041] Optionally, the patches are non-identical and form a non-repeating pattern on the surface of the transparent substrate.

[0042] Optionally, the patches are square patches having a side length of 50-500 pm, preferably 150-350 pm.

[0043] Optionally, the gap has a width of 0.5-5 pm, preferably 2-3 pm.

[0044] According to a second aspect of the invention, a visibly transparent sheet comprising a transparent substrate and the coating according to the first aspect provided on a surface of the transparent substrate is provided. The transparent substrate preferably comprises a glass substrate, such as a glass sheet, wherein the visibly transparent sheet is constituted by the glass substrate / sheet and the coating.

[0045] According to a third aspect, a visibly transparent sheet is provided, comprising: a glass substrate comprising a surface pattern, the surface pattern comprising at least one set of glass structures separated by recesses, each recess comprising one or more first unit cells, and each glass structure comprising one or more second unit cells, the first and second unit cells having identical shapes and sizes as measured in a plane parallel with a top surface of the glass substrate, a first film provided on top of the surface pattern, the first film comprising one of: a first stacked layer mirror film comprising at least a first dielectric layer, a second dielectric layer, and a first metal layer arranged between the first and second dielectric layers, the first stacked layer mirror film being configured to reflect light in an infrared range of light and to transmit light in a visible range of light, and a first transparent conductive oxide film, - wherein the first film comprises first portions provided in the recesses and second portions provided on the structures, and wherein a depth of the recesses is larger than a thickness of the first film.

[0046] The visibly transparent sheet according to the third aspect can be tuned to provide the same optical properties as a visibly transparent sheet according to the second aspect. Sizes and shapes of the first and second unit cells, etc, may be the same as those of the first aspect. Similarly, the structures may have the same height.

[0047] Advantageous features and embodiments of the visibly transparent sheet according to the third aspect are disclosed in the dependent claims.

[0048] According to a fourth aspect of the invention, a window comprising the transparent sheet according to the second aspect or third aspect is provided.

[0049] Further advantages and advantageous features of the invention are disclosed in the following description and in the dependent claims.

[0050] DEFINITIONS

[0051] “Visibly transparent” refers to transparency in the visible wavelength range, i.e. , within the visible range of the electromagnetic spectrum. By a visibly transparent coating or sheet is herein intended a coating or sheet that transmits at least 75% of incident visible light, such that at least 75% of incident visible light passes through.

[0052] “Visible light” as used herein includes light within the wavelength range of 380 nm to 750 nm.

[0053] “Infrared light” as used herein includes light within the wavelength range of 750 nm to 1 mm, wherein a near-infrared wavelength range is 750- 2500 nm. The near-infrared range is hence included in the infrared range. BRIEF DESCRIPTION OF THE DRAWINGS

[0054] With reference to the appended drawings, below follows a more detailed description of embodiments of the invention cited as examples.

[0055] Fig. 1 is a principle view of a coated or patterned sheet according to an example embodiment,

[0056] Fig. 2 is a top view of the coated or patterned sheet shown in Fig. 1 ,

[0057] Fig. 3 is a top view of a patch according to an example embodiment,

[0058] Fig. 4 is a side view of a sheet according to a first embodiment,

[0059] Fig. 5 is a side view of a sheet according to a second embodiment,

[0060] Fig. 6 is a side view of a sheet according to a third embodiment,

[0061] Fig. 7 is a side view of a sheet according to a fourth embodiment,

[0062] Fig. 8 is a diagram illustrating a RF response of the sheet in Fig. 7,

[0063] Fig. 9 is a diagram illustrating a MIR response of the coating in Fig. 7,

[0064] Fig. 10 is a diagram illustrating a NIR response of the coating in Fig. 7,

[0065] Fig. 11 is a diagram illustrating a response of the coating in Fig. 7 in the visible range,

[0066] Fig. 12 is a side view of a sheet according to a fifth embodiment,

[0067] Fig. 13 is a side view of a sheet according to a sixth embodiment ,

[0068] Fig. 14a is a side view of a sheet according to a seventh embodiment in a first state,

[0069] Fig. 14b is a side view of a sheet according to the seventh embodiment in a second state;

[0070] Fig. 15a is a side view of a sheet according to an eighth embodiment in a first state,

[0071] Fig. 15b is a side view of a sheet according to the eighth embodiment in a second state;

[0072] Fig. 16a is a side view of a sheet according to a ninth embodiment in a first state,

[0073] Fig. 16b is a side view of a sheet according to the ninth embodiment in a second state;

[0074] Fig. 17 is a principle view of a coated or patterned sheet according to an alternative design, and

[0075] Fig. 18 is a top view of the coated or patterned sheet shown in Fig. 17.

[0076] The illustrations are schematic and not necessarily drawn to scale. Like reference numbers refer to like elements throughout the description, unless expressed otherwise. DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

[0077] Fig. 1 schematically shows a perspective view of a visibly transparent sheet 200 comprising a transparent substrate 201 , such as a glass substrate, and a coating or surface pattern according to embodiments disclosed herein provided on an upper surface of the transparent substrate 201. Fig. 2 schematically shows a top view of the visibly transparent sheet 200 shown in Fig. 1 and Fig. 3 is an enlarged top view of a single patch 120.

[0078] The coating or surface pattern is formed of a plurality of first unit cells 111a, shown as black squares, and second unit cells 112a, shown as white squares, arranged as an array of patches 120. Each patch 120 comprises a plurality of non-periodically arranged first and second unit cells 111a, 112a. The first and second unit cells 111a, 112a have identical shapes and sizes as measured in a first plane parallel with the surface of the substrate 201, but have different thicknesses as measured in a height direction perpendicular to the first plane, and / or different material configurations as will be further explained below. By identical is herein to be understood as identical within manufacturing tolerances. Each one of the first and second unit cells 111a, 112a may have an area of 4- 400 pm2, preferably 20-300 pm2, as measured in the first plane. Each one of the first and second unit cells 111a, 112a herein has a square shape with a side length a of 2-20 pm, preferably 3-10 pm, as measured in the first plane.

[0079] Each two adjacent patches 120 are separated by a gap 130 having a width c. The patches 120 are herein non-identical and form a non-repeating pattern on the surface of the transparent substrate 201. However, in other embodiments, the patches may be identical and form a repeating pattern on the surface of the transparent substrate 201. The patches 120 are square patches having a side length b of 50-500 pm, preferably 150-350 pm. The gaps 130, which are in the form of linear gaps, may have a width c of 0.5-5 pm, preferably 2-3 pm.

[0080] As indicated in Fig. 1 , the sheet 200 is transparent to visible light (Vis), while as it diffusively scatters electromagnetic radiation in the near infrared (NIR) range, reflects (blocks) electromagnetic radiation in the mid infrared (MIR) range, having wavelengths of 4-15 pm, and transmits electromagnetic radiation of radio frequencies (RF), i.e., 0.1-100 GHz. The first unit cells 111a form recesses 111, each recess 111 comprising one or more first unit cells 111a, and the second unit cells 112a form structures 112, each structure 112 comprising one or more second unit cells 112a. The recesses 111 separate the structures 112 from one another and are to be understood as recessed with respect to a top surface of the structures 112.

[0081] In some embodiments, the visibly transparent sheet 200 comprises a coating 100 comprising a first film 101, which is either a first stacked layer mirror film or a first transparent conductive oxide thin film as will be further described below. The at least one set of structures 112 are arranged in a pattern on top of the first film 101 , all structures 112 being equal or at least similar in material configuration. The structures 112 are separated by the recesses 111. The coating 100 is a discontinuous coating forming the array of patches 120 provided on the surface of the transparent substrate 201. The linear gaps 130 separating the patches 120 from one another are non-coated, naked glass surfaces.

[0082] In other embodiments, the visibly transparent sheet 200 comprises a surface pattern, wherein the structures 112 are glass structures separated by the recesses 111 , formed by etching or similar. Hence, the recesses 111 are formed in the transparent glass substrate 201. Each recess 111 comprises one or more of the first unit cells 111a, and each glass structure comprises one or more of the second unit cells 112a. A first film is provided on top of the surface pattern. The first film comprises first portions provided in the recesses 111 and second portions provided on the structures 112, hence covering a surface of the recesses 111 as well as of the structures 112. A depth of the recesses 111 is larger than a thickness of the first film.

[0083] First embodiment

[0084] A schematic side view of a glass sheet 200 comprising a glass substrate 201 and a coating 100 according to a first embodiment is shown in Fig. 4. The coating 100 comprises a first film 101 , provided on a surface of the glass substrate 201, in the form of a first single-layer transparent conductive oxide (TCO) film. The coating 100 further comprises a second layer structure 110 forming structures 112, wherein the second layer structure 110 is in the form of a single second TCO layer. The coating 100 is configured for diffuse scattering of NIR light, reflection of MIR light and transparency for visible light and RF radiation.

[0085] The transparent conductive oxide, TCO, used for the first film 101 and the second layer structure 110 may be indium tin oxide (ITO), fluorine-doped tin oxide (FTO), or aluminum- doped zinc oxide (AZO). Such films and properties thereof are, e.g., described by: M. Morales-Masis, S. De Wolf, R. Woods-Robinson, J. W. Ager, C. Ballif, Adv. Electron. Mater. 2017, 3, 1600529; H. J. Park, J. Kim, J. H. Won, K. S. Choi, Y. T. Lim, J. S. Shin, J.-U. Park, Thin Solid Films 2016, 615, 8; G. Rey, C. Ternon, M. Modreanu, X. Mescot, V. Consonni, D. Belief, J. Appl. Phys. 2013, 114, 183713; V. Consonni, G. Rey, H. Roussel, B. Doisneau, E. Blanquet, D. Belief, Acta Mater. 2013, 61 , 22; Transparent Conductive Zinc Oxide (Eds: K. Ellmer, A. Klein, B. Rech), Springer, Berlin 2008; A. Klein, J. Am. Ceram. Soc. 2013, 96, 331 ; K. Ellmer, Nat. Photonics 2012, 6, 809.

[0086] The same or different materials may be used for the first film 101 and the second layer structure 110, respectively. TCOs are generally degenerately doped n-type semiconductors that exhibit a high electrical conductivity of 103— 104S cm-1. In the present embodiments, the TCO films may be fabricated as thin films of about 50 nm - 500 nm thickness, such as 100-600 nm, e.g., about 300 nm thickness, in order to show high transparency in the visible range and high reflectance in the near-IR range and in the mid- and far-IR range.

[0087] Second embodiment

[0088] A schematic side view of a glass sheet 200 comprising a glass substrate 201 and a coating 100 according to a second embodiment is shown in Fig. 5. The coating 100 according to the second embodiment is similar to the first embodiment, except in that the first film 101 and the second layer structure 110 comprise stacked layers. The first film 101 is a first stacked layer mirror film comprising five layers:

[0089] - a first dielectric layer 102,

[0090] - a second dielectric layer 104, and

[0091] - a first metal layer 103,

[0092] - a first intermediate layer 106 sandwiched between the first dielectric layer 102 and the first metal layer 103, and

[0093] - a second intermediate layer 109 sandwiched between the first metal layer 103 and the second dielectric layer 104. The first stacked layer mirror film 101 itself is configured to reflect incident light 1 in the NIR range of light and / or IR range of light. It is further configured to transmit light in a visible range of light, such as to transmit at least 75% of incident visible light, preferably at least 80%, more preferably at least 85%, even more preferably at least 90%, or most preferably at least 95% of incident visible light. For this purpose, the first dielectric layer 102 closest to the glass substrate 201 may be a high refractive index dielectric layer such as a TiC>2 layer, a GaP layer, or an HfC>2 layer, preferably a TiC>2 layer, having a thickness within the range of 5 nm-200 nm, preferably 20 nm-50 nm, such as about 20 nm. The second dielectric layer 104 may be a low refractive index dielectric layer, such as an SiC>2 layer or an AI2O3 layer having a thickness within the range of 5 nm-500 nm, preferably 20 nm-70 nm, such as about 50 nm. The first metal layer 103 is herein a noble metal layer such as an Ag layer, a Cu layer, or an Au layer, preferably an Ag layer, having a thickness within the range of 5 nm-40 nm, preferably 5 nm-25 nm, such as about 12 nm.

[0094] The first intermediate layer 106 may be a first ZnO layer having a thickness of 10 nm. The second intermediate layer 109 may be a second ZnO layer having a thickness of 10 nm. The first and second intermediate layers 106, 109 may have the same thicknesses and are preferably made of the same material. The first and second intermediate layers may be semiconductive layers that promote growth of relatively large crystal grains in the first metal layer sandwiched therebetween, reducing electric resistance of the first metal layer and improving its ability to reflect infrared light. ZnO has a crystal structure that helps e.g. Ag to be well-crystalized and grow in a desired direction, making the first stacked layer mirror film 101 more efficient. Alternative materials to ZnO include Zn2SnO4 (zinc stannate), TiO2, ITO, and ZnSe (zinc selenide).

[0095] In some embodiments, the first stacked layer mirror film 101 consists of a first dielectric layer 102 in the form of a TiO2 layer having a thickness of 20 nm, a first intermediate layer 106 in the form of a ZnO layer having a thickness of 10 nm, a first metal layer 103 in the form of an Ag layer having a thickness of 12 nm, a second intermediate layer 109 in the form of a ZnO layer having a thickness of 10 nm, and a second dielectric layer 104 in the form of an SiO2 or AI2O3 layer having a thickness of 50 nm.

[0096] The first metal layer 103 herein acts as a reflector, while as the second dielectric layer forms a spacing layer between the reflector and the nanostructures 111 , 112. The intermediate layers 106, 109 improve the optical properties of the metal layer as described above. Thicknesses of films and layers may herein be determined using, for example, spectroscopic ellipsometry, atomic force microscopy, or profilometry.

[0097] The first stacked layer mirror film 101 provides specular reflection in the IR range while being fully transparent in the visible. It is thus comparable to a standard Low-E glass.

[0098] In the illustrated second embodiment, the structures 112 have a five-layer structure with the same configuration, or at least a similar configuration, as the first stacked layer mirror film 101 . The structures 112 hence comprise a second stacked layer structure 110 comprising:

[0099] - a third dielectric layer 113,

[0100] - a fourth dielectric layer 115, and

[0101] - a second metal layer 114 sandwiched between the third and fourth dielectric layers 113, 115,

[0102] - a third intermediate layer 116 sandwiched between the third dielectric layer 113 and the second metal layer 114, and

[0103] - a fourth intermediate layer 119 sandwiched between the second metal layer 114 and the fourth dielectric layer 115.

[0104] The third dielectric layer 113 closest to the first film 101 is herein provided directly on the second dielectric layer 104. It may be a TiC>2 layer, a GaP layer, or an HfC>2 layer, preferably a TiC>2 layer, having a thickness within the range of 5 nm-200 nm, preferably 20 nm-50 nm, such as about 20 nm. The fourth dielectric layer 115 may be an SiC>2 layer or an AI2O3 layer having a thickness within the range of 5 nm-500 nm, preferably 20 nm- 70 nm, such as about 50 nm. The second metal layer 114 is a noble metal layer such as an Ag layer, a Cu layer, or an Au layer, preferably an Ag layer, having a thickness within the range of 5 nm-40 nm, preferably 5 nm-25 nm, such as about 12 nm. In some embodiments, the second stacked layer structure 110 consists of a third dielectric layer 113 in the form of a TiC>2 layer having a thickness of 20 nm, a third intermediate layer 116 in the form of a ZnO layer having a thickness of 10 nm, a second metal layer 114 in the form of an Ag layer having a thickness of 12 nm, a fourth intermediate layer 119 in the form of a ZnO layer having a thickness of 10 nm, and a fourth dielectric layer 115 in the form of an SiO2 or AI2O3 layer having a thickness of 50 nm. In the second embodiment, the coating 100 is configured for reflection and diffuse scattering of incident infrared light and for transmission of visible light in the solar spectrum. Hence, of the incident light, a NIR portion is diffusively scattered, a MIR portion is reflected, while a visible portion and a RF portion is transmitted through the coating 100 and the glass substrate 201. An incidence of the solar light can be any, i.e., from fully grazing to normal.

[0105] Third embodiment

[0106] A schematic side view of a transparent glass sheet 200 in the form of a patterned glass substrate 600 comprising a surface pattern according to a third embodiment is shown in Fig. 6. In the third embodiment, the surface pattern comprises at least one set of glass structures 112 separated by recesses 111, each recess 111 comprising one or more first unit cells 111a, and each glass structure comprising one or more second unit cells 112a as described with reference to Figs. 1-3 above. A first film 601 is provided on top of the surface pattern, wherein the first film 601 has a thickness which is smaller than a depth d of the recesses 111, such that the first film 601 is a discontinuous film. The first film 601 herein comprises a first transparent conductive oxide (TCO) film, which may have the same properties as the TCO film used in the first embodiment illustrated in Fig. 4. The first film comprises first portions 601a provided in the recesses 111 , covering the recesses

[0107] 111 , and second portions 601b provided on the structures 112, covering the structures

[0108] 112.

[0109] The depth d of the recesses may be within the range of 0.05-1 pm, preferably 0.05-0.8 pm. A thickness of the first film 601 may be within the range of 0.05-1 pm, preferably 0.1- 1 pm.

[0110] The linear gaps 130 separating the patches 120 from one another are herein part of the glass structures 112, but without any coating provided thereon. In other words, the gaps 130 are elevated with respect to the first unit cells 111a of the recesses 111, but less elevated than the second unit cells 112a comprising the second portions 601b of the first film 601 on top of the structures 112. Hence, the gaps 130 are non-coated glass surfaces. In other embodiment, the linear gaps may form part of the recesses. The transparent sheet 200 according to the third embodiment is configured for diffuse scattering of NIR light, reflection of MIR light and transparency for visible light and RF radiation.

[0111] Fourth embodiment

[0112] A schematic side view of a transparent glass sheet 200 in the form of a patterned glass substrate 600 comprising a surface pattern according to a fourth embodiment is shown in Fig. 7. The glass sheet 200 according to the fourth embodiment is similar to the third embodiment, except in that the first film 601 comprises stacked layers having the same configuration as in the second embodiment illustrated in Fig. 5. Hence, the first film 601 comprises:

[0113] - a first dielectric layer 602,

[0114] - a second dielectric layer 604,

[0115] - a first metal layer 603,

[0116] - a first intermediate layer 606 sandwiched between the first dielectric layer 102 and the first metal layer 603, and

[0117] - a second intermediate layer 609 sandwiched between the first metal layer 603 and the second dielectric layer 604.

[0118] Materials, thicknesses, etc., may be the same as those of the first film 101 according to the second embodiment. Similar to the third embodiment, the depth d of the recesses 111 is larger than the thickness of the first film 601.

[0119] The transparent sheet 200 according to the fourth embodiment is configured for diffuse scattering of NIR light, reflection of MIR light and transparency for visible light and RF radiation. Optical properties of the transparent sheet 200 according to the fourth embodiment are illustrated in Figs. 8-11. Fig. 8 shows simulated total reflectance Rtotai, total transmission Ttotai and absorbance A in the RF range. Fig. 9 shows simulated total reflectance Rtotai, total transmission 7totai and absorbance A in the MIR range. Fig. 10 shows simulated total reflectance Rtotai, specular reflectance Rspecuiar, diffuse reflectance diffuse, total transmission 7totai and absorbance A in the NIR range. Fig. 11 shows simulated total reflectance Rtotai, total transmission 7totai and absorbance A in the visible range. The transparent sheet 200 according to the fourth embodiment is configured for diffuse scattering of NIR light, reflection of MIR light and transparency for visible light and RF radiation. Fifth embodiment

[0120] A schematic side view of a transparent glass sheet 200 in the form of a patterned glass substrate 600 comprising a surface pattern according to a fifth embodiment is shown in Fig. 12. The transparent glass sheet 200 according to the fifth embodiment is similar to the fourth embodiment illustrated in Fig. 7, but the configuration of the first film 601 is different. The transparent sheet 200 according to the fifth embodiment is configured for diffuse scattering of NIR light, reflection of MIR light and transparency for visible light and RF radiation.

[0121] The first film 601 is in the fifth embodiment a first stacked layer mirror film 601 having a five-layer structure. It comprises a first dielectric layer 602 provided closest to the glass substrate surface, a second dielectric layer 604 provided as a top layer, and a first metal layer 603 arranged between the first and second dielectric layers 602, 604. The first stacked layer mirror film 601 is configured to reflect light in an infrared range of light and to transmit light in a visible range of light. The first stacked layer mirror film 601 further comprises a first intermediate layer 606 and a spacer layer 607, wherein the first intermediate layer 606 is sandwiched between the first metal layer 603 and the spacer layer 607. Hence, as seen from the glass substrate surface, the first film 601 comprises:

[0122] - the first dielectric layer 602, such as a TiC>2 layer,

[0123] - the spacer layer 607, such as a SiC>2 layer,

[0124] - the first intermediate layer 606, such as a TiC>2 layer,

[0125] - the first metal layer 603, such as an Ag layer, and

[0126] - the second dielectric layer 604, such as a TiC>2 layer.

[0127] Similar to the third embodiment, the depth of the recesses 111 is larger than the thickness of the first film 601.

[0128] Sixth embodiment

[0129] A schematic side view of a transparent glass sheet 200 in the form of a patterned glass substrate 600 comprising a surface pattern according to a sixth embodiment is shown in Fig. 13. The transparent glass sheet 200 according to the sixth embodiment is similar to the fourth embodiment illustrated in Fig. 7, but the configuration of the first film 601 is different. The transparent sheet 200 according to the sixth embodiment is configured for diffuse scattering of NIR light, reflection of MIR light and transparency for visible light and RF radiation.

[0130] Instead of a five-layer structure, the first film 601 of the sixth embodiment has a three- layer structure with a first transparent conductive oxide layer 611 , a second transparent conductive oxide layer 613, and a metal layer 612 sandwiched between the first and second transparent conductive oxide layers 611 , 613. The metal layer 612 may be a noble metal layer such as an Ag layer, and the first and second transparent conductive oxide layers 611 , 613 may be ITO layers. Alternatively, they may comprise fluorine-doped tin oxide (FTO), or aluminum-doped zinc oxide (AZO).

[0131] Seventh embodiment

[0132] Figs. 14a-b show schematic illustrations of a transparent glass sheet 200 in the form of a patterned glass substrate 600 comprising a surface pattern according to a seventh embodiment. In this embodiment, the glass substrate 600 comprises a patterned portion 610 of SiO2 and a conductive layer 605 in the form of a transparent metal grid, such as a Cu grid, or a layer of crossed metal nanowires embedded between a main portion of the glass substrate 600 and the patterned portion 610. Electrodes 608 for applying a voltage to the conductive layer 605 are furthermore provided, thereby heating it to raise a temperature of the first film 601 . The first film 601 is configured to be actively switched between diffuse scattering and absorption of incident IR light as the temperature is increased above a threshold.

[0133] The first film 601 is a stacked layer film comprising a transparent conductive oxide (TCO) layer 620, such as an ITO layer, closest to the patterned portion 610, a first dielectric layer 621 , such as a TiO2 layer, and a second dielectric layer 623, such as a TiO2 layer, provided as a top layer. Between the first and second dielectric layers 621 , 623, a phasechange material layer 622 is provided.

[0134] The phase-change material layer 622 may consist of a thermally switchable phase-change material having a transition temperature above which it is metallic and below which it is dielectric, such as VO2 or doped VO2. Thereby, above the transition temperature, the first film 601 will absorb NIR radiation and convert it into heat as illustrated in Fig. 14b, while as below the transition temperature, the first film 601 will diffusively scatter NIR light as illustrated in Fig. 14a. Similar to the third embodiment, the depth of the recesses 111 is larger than the thickness of the first film 601.

[0135] Eighth embodiment

[0136] Figs. 15a-b show schematic illustrations of a transparent glass sheet 200 in the form of a patterned glass substrate 600 comprising a surface pattern according to an eighth embodiment. In this embodiment, the first film 601 has a five-layer structure comprising, as seen from the glass substrate 600:

[0137] - a first TCO layer 630,

[0138] - a lossy metal layer 631 , such as a Ti layer,

[0139] - a dielectric layer 632, Such as a TiC>2 layer,

[0140] - a phase-change material layer 622, such as in the seventh embodiment,

[0141] - a second TCO layer 633.

[0142] The lossy metal layer is made of a metal having a high absorption of the visible light and also high electrical (ohmic) resistance, such as a Cr layer, a Ti layer, or an Fe layer, or possibly a Ni layer. The lossy metal layer 631 may have a thickness of 30 nm or less, such as 10-12 nm. These metals have lower electric conductivity than the noble metals and hence the first film 601 has a different response to incident electromagnetic radiation than when a noble metal layer is used. The lossy metal layer 631 of the first film 601 in combination with the surface pattern lead to absorption of incident NIR light and hence a heating of the sheet 200 is achieved as illustrated in Fig. 15a. Once the sheet 200 is heated to a transition temperature of the phase-change material layer 622, the VO2 material will turn metallic and the first film 601 in combination with the surface pattern will instead lead to a diffuse scattering of incident NIR radiation as illustrated in Fig. 15b.

[0143] Thus, in this embodiment, the transparent glass sheet 200 is configured such that, above the transition temperature, the first film 601 will diffusively scatter NIR radiation as illustrated in Fig. 15b, while as below the transition temperature, the first film 601 will absorb NIR light and turn it into heat as illustrated in Fig. 15a.

[0144] Similar to the third embodiment, the depth of the recesses 111 is larger than the thickness of the first film 601. Ninth embodiment

[0145] Figs. 16a-b show schematic illustrations of a transparent glass sheet 200 in the form of a patterned glass substrate 600 comprising a surface pattern 660 of SiC>2 according to a ninth embodiment. In this embodiment, the first film 601 comprises a first transparent conductive oxide film 601, such as an ITO film, coated onto the surface pattern 660, wherein the surface pattern 660 comprises the recesses 111 and the structures 112. The visibly transparent sheet 200 further comprises a second stacked layer mirror film 650 provided between a top surface of the glass substrate 600, and the surface pattern 660. The second stacked layer mirror film 650 has a five-layer structure comprising, as seen from the glass substrate 600:

[0146] - a first dielectric layer 651 , such as a TiO2 layer,

[0147] - a first metal layer 652, such as a noble metal layer, e.g., an Ag layer,

[0148] - a phase-change material layer 622, such as an LCE layer,

[0149] - a second metal layer 653, such as a noble metal layer, e.g., an Ag layer,

[0150] - a second dielectric layer 654, such as a TiC>2 layer.

[0151] The gaps 130 correspond to the top surface of the glass substrate 600, i.e., they are recessed with respect to the first film 601 as well as with respect to the second stacked layer mirror film 650. The second stacked layer mirror film 650 is hence discontinuous.

[0152] The phase-change material layer 622 may consist of a liquid crystal elastomer, LCE, layer changing its thickness when heated. Under sun illumination, NIR radiation is absorbed and actuates the LCE layer 622 by heating as illustrated in Fig. 16a, and when the LCE is heated enough to expand, it turns into a diffuser, diffusively scattering NIR light as illustrated in Fig. 16b.

[0153] Similar to the third embodiment, the depth of the recesses 111 is larger than the thickness of the first film 601.

[0154] Alternative design

[0155] Figs. 17 and 18 show an alternative design of a visibly transparent sheet 800 comprising a coating 900 provided on a transparent substrate 801 , such as a glass substrate. The coating 100 comprises disks 812a of uniform shapes and sizes provided on a discontinuous thin film 811, wherein the disks 812a form agglomerates 812. The thin film 811 and the disks 812a may have the same configuration as any one of the first films and the structures described with reference to Figs. 1-16, respectively, wherein the disks 812a correspond to the second unit cells 112a. Hence, the visibly transparent sheet may either comprise a coating 900 as shown in Fig. 17, or it may comprise a surface pattern and a first film provided on top of the surface pattern. The agglomerates 812 may be formed using disk agglomeration and hole-mask colloidal lithography (HCL), i.e. , using self-assembled colloidal polymer nanospheres to create masks. The disk diameter d as measured in a plane parallel with the surface may vary from 100 nm to 5 pm, and the agglomerates 812 may have average sizes of 2 to 25 pm, depending on the disk diameter. The coating or surface pattern comprises a plurality of agglomerates 812, arranged as an array of patches 820 having a side length b. Each two adjacent patches 820 are separated by a gap 830 having a witch c. Sizes of the patches 820 and gaps 830 may correspond to those described with reference to Figs. 1-16. The patches 820 are non-identical and form a non-repeating pattern on the surface of the transparent substrate 801.

[0156] In all embodiments described above, it is possible to add a coloring layer on top of the visibly transparent sheet 200, such as a layer of semiconducting or metallic nanostructures configured to produce a colored appearance by interaction with incident light. The nanostructures may be in the form of spheres, disks, or similar, and they may have equivalent diameters of 1-1000 nm, such as 10-800 nm. The nanostructures may be made of any suitable high-refractive index material, preferably a semiconducting material such as Si. The coloring layer can be tuned, e.g. by selecting a suitable size of the nanostructures, to produce various colors such as blue, green, yellow, etc. This provides a visually appealing sheet making architectural structures more attractive while maintaining the transparency of the glass.

[0157] The coloring layer may cover the entire visibly transparent sheet 200, including the gaps 130 between the patches 120. In some embodiment, the color layer may be provided below the coating 100, directly on top of the substrate 201. The sizes of the nanostructures should be adapted in view of the refractive index of the materials surrounding the color layer, such that a desired color is achieved. The color layer may, e.g., be produced by any suitable lithography method, such as colloidal lithography or similar, or by simply spreading pre-synthesised metallic and / or semiconducting particles provided in a liquid onto the surface of the sheet.

[0158] It is to be understood that the present invention is not limited to the embodiments described above and illustrated in the drawings; rather, the skilled person will recognize that many changes and modifications may be made within the scope of the appended claims.

Claims

CLAIMS1. A visibly transparent coating (100) for a transparent substrate (201) such as a glass substrate (201), wherein the coating (100) is configured to be provided on a surface of the transparent substrate (201) and comprises: a first film (101) comprising one of: a first stacked layer mirror film (101) comprising at least a first dielectric layer (102), a second dielectric layer (104), and a first metal layer (103) arranged between the first and second dielectric layers (102, 104), the first stacked layer mirror film (101) being configured to reflect light in an infrared range of light and to transmit light in a visible range of light, and a first transparent conductive oxide film (101), at least one set of structures (112) arranged in a pattern on a top surface of the first film (101), the structures (112) being separated by recesses (111) comprising one or more empty first unit cells (111a), each structure (112) within the at least one set of structures (112) comprising one or more second unit cells (112a), the first and second unit cells (111a, 112a) having identical shapes and sizes as measured in a plane parallel with the top surface of the first film,- wherein each one of the second unit cells (112a) comprise at least a second layer structure (110) comprising one of: a second stacked layer structure (110) comprising at least a third dielectric layer (113), a fourth dielectric layer (115), and a second metal layer (114) arranged between the third and fourth dielectric layers (113, 115), and a second transparent conductive oxide layer (110).

2. The coating according to claim 1 , wherein each one of the first and second unit cells (111a, 112a) has an area of 4-400 pm2, preferably 20-300 pm2, as measured in said plane.

3. The coating according to claim 1 or 2, wherein each one of the first and second unit cells (111a, 112a) has a square shape with a side length (a) of 2-20 pm, preferably 3-10 pm, as measured in said plane.

4. The coating according to any one of the preceding claims, wherein the pattern is formed by using an optimization algorithm that combines the first and second unit cells to minimize specular reflection of near-infrared light.

5. The coating according to any one of the preceding claims, wherein the at least one set of structures (112) covers 30-70% of the first film, preferably 40-60%.

6. The coating according to any one of the preceding claims, wherein the structures (112) have a height of 0.05-1 pm, preferably 0.1-0.8 pm, more preferably 0.1-0.4 pm, as measured in a direction perpendicular to said plane.

7. The coating according to any one of the preceding claims, wherein the visibly transparent coating (100) is configured for diffuse scattering of light within a near infrared range of light.

8. The coating according to claim 7, wherein the structures (112) comprise the second stacked layer structure (110), and wherein the second metal layer (114) is a noble metal layer, preferably a silver layer, a gold layer, or a copper layer, most preferably a silver layer.

9. The coating according to any one of the preceding claims, wherein the first stacked layer mirror film further comprises a first intermediate layer sandwiched between the first metal layer (103) and the first dielectric layer (102), and / or a second intermediate layer sandwiched between the first metal layer (103) and the second dielectric layer (104).

10. The coating according to any one of the preceding claims, wherein the second stacked layer structure (110) further comprises a third intermediate layer sandwiched between the second metal layer and the third dielectric layer (113), and / or a fourth intermediate layer sandwiched between the second metal layer and the fourth dielectric layer (115) .

11. The coating according to any one of the preceding claims, wherein the second unit cells (112a) further comprise at least one phase-change material layer (116) or a liquid crystal elastomer layer (116), and / orwherein the coating (100) further comprises a third film arranged between the first film and the at least one set of structures, wherein the third film comprises a phasechange material layer or a liquid crystal elastomer layer.

12. The coating according to claim 11 , wherein the first film comprises the first stacked layer mirror film (101), the second unit cells (112a) comprise the second stacked layer structure (110), and wherein the phase-change material layer is arranged between the second dielectric layer (104) and the third dielectric layer (113).

13. The coating according to claim 11 or 12, wherein the at least one phase-change material layer comprises a thermally or electrically, preferably thermally switchable phasechange material having a transition temperature above which it is metallic and below which it is dielectric.

14. The coating according to any one of the preceding claims, wherein the coating (100) is a discontinuous coating in the form of an array of patches (120) configured to be provided on the surface of the transparent substrate (201), each two adjacent patches (120) being separated by a gap (130), each patch (120) comprising said at least one set of structures (112) separated by said recesses (111).

15. The coating according to claim 14, wherein the patches (120) are identical and form a repeating pattern on the surface of the transparent substrate (201).

16. The coating according to claim 14, wherein the patches (120) are non-identical and form a non-repeating pattern on the surface of the transparent substrate (201).

17. The coating according to any one of claims 14-16, wherein the patches (120) are square patches having a side length of 50-500 pm, preferably 150-350 pm, and / or wherein the gap (130) has a width (c) of 0.5-5 pm, preferably 2-3 pm.

18. A visibly transparent sheet (200) comprising a transparent substrate (201), such as a glass substrate, and the coating (100) according to any one of the preceding claims provided on a surface of the transparent substrate (201).

19. A visibly transparent sheet (200), comprising:a glass substrate (600) comprising a surface pattern, the surface pattern comprising at least one set of glass structures separated by recesses, each recess comprising one or more first unit cells (111a), and each glass structure comprising one or more second unit cells (112a), the first and second unit cells (111a, 112a) having identical shapes and sizes as measured in a plane parallel with a top surface of the glass substrate, a first film (601) provided on top of the surface pattern, the first film (601) comprising one of: a first stacked layer mirror film comprising at least a first dielectric layer (602), a second dielectric layer (604), and a first metal layer (603) arranged between the first and second dielectric layers (602, 604), the first stacked layer mirror film being configured to reflect light in an infrared range of light and to transmit light in a visible range of light, and a first transparent conductive oxide film,- wherein the first film (601) comprises first portions (601a) provided in the recesses (111) and second portions (601b) provided on the structures (112), and wherein a depth (d) of the recesses (111) is larger than a thickness of the first film (601).

20. The visibly transparent sheet according to claim 19, wherein the first film (601) comprises two layers (611, 613) of the transparent conductive oxide film, and a metal layer (612) sandwiched between the two layers of the transparent conductive oxide film.

21. The visibly transparent sheet according to claim 19 or 20, wherein the first film (601) further comprises at least one phase-change material layer (622).

22. The visibly transparent sheet according to claim 21 , wherein the first film (101) comprises the transparent conductive oxide film (620) and two dielectric layers (621, 623), and wherein the phase-change material layer (622) is sandwiched between the two dielectric layers (621 , 623).

23. The visibly transparent sheet according to claim 21 or 22, wherein the at least one phase-change material layer (622) comprises a thermally switchable phase-change material having a transition temperature above which it is metallic and below which it is dielectric.

24. The visibly transparent sheet according to any one of claims 21-23, wherein the first film comprises two layers (630, 633) of the transparent conductive oxide film, and wherein the thermally switchable phase-change material layer (622) is provided between the two layers of the transparent conductive oxide film.

25. The visibly transparent sheet according to claim 24, further comprising a lossy metal layer (631) and a dielectric layer (632) arranged between the two layers (630, 633) of the transparent conductive oxide film.

26. The visibly transparent sheet according to claim any one of claims 19-25, further comprising an embedded conductive layer (605), such as a transparent metal grid, arranged below a patterned portion (610) comprising the surface pattern.

27. The visibly transparent sheet according to any one of claims 19-26, wherein the first stacked layer mirror film further comprises a first intermediate layer (606) sandwiched between the first metal layer (603) and the first dielectric layer (602), and / or a second intermediate layer (609) sandwiched between the first metal layer (603) and the second dielectric layer (604).

28. The visibly transparent sheet according to claim 19, wherein the first film (601) comprises the first transparent conductive oxide film, and wherein the visibly transparent sheet (200) further comprises a second stacked layer mirror film (650) provided between a top surface of the glass substrate and the surface pattern (660).

29. The visibly transparent sheet according to claim 28, wherein the second stacked layer mirror film (650) comprises a liquid crystal elastomer layer (622).

30. The visibly transparent sheet according to any one of claims 19-29, wherein the surface pattern forms an array of patches (120) on top of the glass substrate, each two adjacent patches (120) being separated by a gap (130) comprising a non-coated glass surface portion.

31. The visibly transparent sheet according to claim 30, wherein the patches (120) are identical and form a repeating pattern on the surface of the glass substrate (600).

32. The visibly transparent sheet according to claim 30, wherein the patches (120) are non-identical and form a non-repeating pattern on the surface of the glass substrate (600).

33. The visibly transparent sheet according to any one of claims 30-32, wherein the patches (120) are square patches having a side length of 50-500 pm, preferably 150-350 pm, and / or wherein the gap has a width (c) of 0.5-5 pm, preferably 2-3 pm.

34. The visibly transparent sheet according to any one of claims 18-33, further comprising a coloring layer comprising nanostructures configured to produce a colored appearance by interaction with incident light.

35. A window comprising the visibly transparent sheet according to any one of claims 18-34.

Images