Luminescent solar concentrators and luminescent glazing units

Technical field

The invention relates luminescent solar concentrators and luminescent glazing units, and, in particular, though not exclusively, to luminescent solar concentrators and luminescent glazing comprising one or more transparent luminescent coated glazing panes.

Luminescent solar concentrators (LSCs) aim at lowering cost of solar energy generation using a cheap luminescent plate to concentrate solar radiation onto small-area strip-type photovoltaic devices arranged along the sides of the plate. In such scheme sunlight is absorbed by the luminescent material in the plate and re-emitted in all directions. A considerable fraction of the light is trapped in the plate by total internal reflection. This way the plate acts as a light guide wherein the re-emitted light is guided to the perimeter of the plate where photovoltaic devices convert the light into electric power.

US 20210280727 A1 describes luminescent solar concentrators and luminescent glazing units comprising one or more luminescent coated glazing panes. Examples of such luminescent layers include Sm2+ and Tm2+ doped SiAION coatings which absorb light in the UV/NUV band and then transmits radiation in a narrow band in the red/NIR band that can be optimized to the obsorption band of the PV cells.

It is desirable to improve the luminescence output of luminescent coated glazing panes. In particular, it is desirable to improve the edge emission of the luminescent coated glazing panes, which occurs when photons produced by a luminescent coating a glazing pane are reflected within the substrate and exit the substrate edges. This way, the output power of such luminescent solar concentrators and/or luminescent glazing units can be optimized.

The embodiments in this disclosure aim to provide luminescent solar concentrators and/or luminescent glazing units. More particularly, the invention aims to provide luminescent solar concentrators and/or luminescent glazing units comprising a luminescent layer. In first aspect the embodiments in this disclosure relate to a luminescent solar concentrator or a luminescent glazing unit comprising a transparent sheet of glazing material with a first surface, a second surface opposite the first surface, and an edge surface, wherein the first surface comprises a first coating comprising a luminescent layer and the second surface comprises a second coating comprising a first silver layer.

In second aspect the embodiments in this disclosure relate to a luminescent solar concentrator or a luminescent glazing unit comprising a transparent sheet of glazing material with a first surface, a second surface opposite the first surface, and an edge surface, wherein the first surface comprises a first coating comprising a luminescent layer and the second surface comprises a second coating comprising a first silver layer.

The inventors have discovered that the luminescence output, and in particular the edge emission, of the luminescent glazing unit is substantially increased by the addition of a silver layer on a second surface opposite the luminescent layer.

Here, a surface comprises a coating may include a coating is directly or indirectly adhered to the surface of the glazing material. A coating comprsing a layer may imply that the layer is within the coating, the coating may or may not comprise further layers above or below the layer.

In an aspect, the embodiments may relate to a glazing unit comprising: a first glazing pane comprising a transparent sheet of glazing material with a first surface, a second surface opposite the first surface, and an edge surface, a first luminescent coating provided over the first surface and a second reflecting coating provided over the second surface, the reflecting coating comprising a first siver containing layer.

In an embodiment, the glazing unit may further comprise a photovoltaic module, preferably the photovoltaic module being optically connected to at least part of the edge surface of the first first glazing pane.

In an embodiment, the glazing unit may further comprise a second glazing pane in a face-to-face spaced apart configuration with the first glazing pane to form a cavity therebetween.

In a further aspect, the embodiments may relate to a luminescent solar concentrator comprising: a first glazing pane comprising a transparent sheet of glazing material with a first surface, a second surface opposite the first surface, and an edge surface, a first luminescent coating provided over the first surface and a second reflecting coating provided over the second surface, the reflecting coating comprising a first siver containing layer and, a photovoltaic module optically connected to at least part of the edge surface of the first first glazing pane.

In an embodiment, the luminescent layer mau comprise Sm ²⁺ and/or Tm ²⁺ and/or Mn ⁵⁺ . In an embodiment, the luminescent layer may be a homogenous luminescent layer, preferably the homogenous luminescent layer is provided by sputtering.

In an embodiment, the homogenous luminescent layer may comprise silicon, aluminium, oxygen and nitrogen, and wherein the homogenous luminescent layer further comprises Sm ²⁺ and/or Tm ²⁺ and/or Mn ⁵⁺ .

In an embodiment, the luminescent layer may comprise luminescent particles, microparticles and/or nanoparticles in a matrix material.

In an embodiment, the luminescent particles, microparticles and/or nanoparticles may comprise silicon, aluminium, oxygen and nitrogen, and wherein the luminescent particles, microparticles and/or nanoparticles further comprise Sm ²⁺ and/or Tm ²⁺ and/or Mn ⁵⁺ .

In an embodiment, the luminescent layer of the the glazing unit or the luminescent solar concentrator may comprise silicon, aluminium, samarium, oxygen and nitrogen, and wherein the luminescent layer comprises an atomic percentage of silicon a, an atomic percentage of aluminium p, an atomic percentage of samarium £, an atomic percentage of oxygen x, and an atomic percentage of nitrogen y, wherein x > y.

In an embodiment, the atomic percentage of nitrogen y is from 0.1 to 15, preferably y is from 1 to 10%, more preferably y is from 2 to 5%.

In an embodiment, the luminescent layer of the the glazing unit or the luminescent solar concentrator comprises samarium with an oxidation state of 2+, and an atomic percentage of samarium with an oxidation state of 2+ is greater than or equal to an atomic percentage of samarium with an oxidation state of 3+.

In an embodiment, a is from 25 to 40%, is from 1 to 5%, £ is from 0.01 to 5%, and x is from 40 to 70%, more preferably wherein a is from 30 to 35%, p is from 2 to 4%, E is from 0.1 to 0.5%, and x is from 50 to 60%.

In an embodiment, the luminescent layer is substoichiometric in oxygen.

In an embodiment, the luminescent layer has a thickness of from 500 to 5000 nm, preferably from 1000 to 2500 nm, more preferably from 1250 to 2250 nm.

In an embodiment, the second coating of the glazing unit or a luminescent solar concentrator may be a low-emissivity or infra-red reflecting coating suitable for architectural glazing.

In an embodiment, the first silver containing layer may have a thickness from 1 to 20 nm, preferably from 4 to 10 nm.

In an embodiment, the second coating may comprise a second silver containing layer, preferably the second silver containing layer has a thickness from 1 to 20 nm, preferably from 4 to 10 nm. In an embodiment, the second coating may comprise, in sequence from the second surface: a base layer adjacent to and in contact with the second surface; a first silver containing layer; and an upper dielectric layer.

In an embodiment, the second coating may comprise a growth promotion layer in contact with the first silver layer between the first silver layer and the second surface, preferably the growth promotion layer comprises an oxide of zinc.

In embodiment, the second coating may be a low-emissivity or infra-red reflecting coating suitable for architectural glazing.

In an embodiment, the transparent sheet of glazing material may comprise glass comprising less than 1% iron oxide, preferably less than 0.1% iron oxide, more preferably less than 0.03% iron oxide.

In an embodiment, the transparent sheet of glazing material may comprise heat treated glass.

First coating

The luminescent layer may be provided with a range of compositions. Preferably the luminescent layer is an amorphous or crystalline coating layer, preferably produced via sputtering.

In another embodiment, the luminescent layer may include luminescent nanoparticles and/or microparticles in a transparent material. In an embodiment, luminescent particles may include a Sm2+, Mn5+ and/or Tm2+ doped material. In an embodiment, the particles may comprise a SiAION:Sm ²⁺ material

In an embodiment, a luminescent polymeric coating and/or lamination may be realized by embedding the particles in a suitable (organic) matrix material. Selection and optimization of polymer matrix material may be based on their applications and conditions. Epoxy resin, poly(methyl methacrylate), poly(siloxane), polycarbonate, polyurethane, polyvinyl butyral, ethylene-vinyl acetate, etc. are some common materials that can be used as a matrix material for these particles.

In an embodiment, the luminescent layer may comprise silicon, aluminium, samarium, oxygen and nitrogen, and wherein the luminescent layer comprises an atomic percentage of silicon a, an atomic percentage of aluminium p, an atomic percentage of samarium E, an atomic percentage of oxygen x, and an atomic percentage of nitrogen y, wherein x > y. The inventors have found that such layers are highly luminescent and may be produced in a repeatable manner.

In an embodiment, the luminescent layer may be homogenous in samarium. A luminescent layer that is homogenous in samarium is where the samarium atoms are dispersed evenly through the layer, rather than being incorporated in clumps, particles or other bodies. A luminescent layer that is homogenous in samarium provides an evenly distributed output of luminesced photons.

In an embodiment, the atomic percentage of nitrogen y may be from 0.1 to 15, preferably y is from 1 to 10, more preferably y is from 2 to 5. The inventors have found that such layers are highly luminescent and may be produced in a highly repeatable manner.

In an embodiment, the luminescent layer may comprise samarium with an oxidation state of 2+, and an atomic percentage of samarium with an oxidation state of 2+. In an embodiment, the atomic percentage of samarium with an oxidation state of 2+ may be greater than or equal to an atomic percentage of samarium with an oxidation state of 3+ The oxidation states of samarium coating components may be assessed, for example, via XPS. The inventors have found that an increased proportion of samarium with an oxidation state of 2+ is associated with a highly luminescent layer.

In embodiment, a is from 25 to 40, p is from 1 to 5, E is from 0.01 to 5, and x is from 40 to 70, more preferably a is from 30 to 35, is from 2 to 4, E is from 0.1 to 0.5, and x is from 50 to 60. The inventors have found that such atomic proportions are associated with highly luminescent layers.

In an embodiment, the luminescent layer may be substoichiometric in oxygen. The inventors have found that a luminescent layer that is substoichiometric in oxygen is more luminescent that those that are not substoichiometric in oxygen.

In an embodiment, the luminescent layer may have a thickness of from 500 to 5000 nm, preferably from 1000 to 2500 nm, more preferably from 1250 to 2250 nm. Such thicknesses are chosen considering the desire for luminescent coatings to be produced efficiently. However, even thicker or even thinner coatings may be used where required by the particular application.

The luminescent layer comprising silicon, aluminium, samarium, oxygen and nitrogen may be the only layer on the first surface. However, in some embodiments there may be underlayers and or overlayers provided. Preferred underlayers include oxides and/or nitrides, such as silicon and/or aluminium oxides, silicon and/or aluminium nitrides, silicon and/or aluminium oxynitrides. In some embodiments overlayers may be provided for increased durability.

In some embodiments, over and/or underlayers may include transparent conductive layers, such as those comprising fluorine doped tin oxide.

The substrate may comprise only one luminescent layer comprising silicon, aluminium, samarium, oxygen and nitrogen. However, the substrate may comprise more than one coating layer comprising silicon, aluminium, samarium, oxygen and nitrogen, preferably separated by additional intermediate layers. Intermediate layers may include, for example, oxides and/or nitrides such as silicon and/or aluminium oxides, silicon and/or aluminium nitrides, silicon and/or aluminium oxynitrides.

Second Coating

The second surface comprises a second coating comprising a first silver containing layer.

In an embodiment, the second coating may be a low emissivity or infra-red reflecting coating suitable for architectural glazing. The combination of such a coating with a first coating comprising a luminescent layer allows for the use of the sheet of glazing material as a glazing pane in glazing units that meet legislative requirements for energy efficiency and heat rejection. Surprisingly, such a coating also enhances the performance of the substrate by increasing the luminescent edge emission.

In an embodiment, the first silver containing layer may have a thickness from 1 to 20 nm, preferably from 4 to 10 nm. The inventors have discovered that such thicknesses allow for the production of a luminescent coated substrate which meets legislative requirements, increases luminescent edge emission, and still maintains a high visible light transmission of the luminescent coated substrate.

In some embodiments, the second coating may comprise a second silver containing layer. Such coatings may be known as “double silver” coatings. Further silver containing layers may be envisaged, providing “triple silver”, “quadruple silver” or higher order low-emissivity layers. Such coatings may improve the heat rejection performance of the luminescent coated substate.

In an embodiment, the second silver containing layer may have a thickness from 1 to 20 nm, preferably from 4 to 10 nm.

The silver containing layer(s) may consist essentially of silver without any additive, as is normally the case in the area of low-emissivity and/or solar control coatings. It is, however, within the scope of the invention to modify the properties of the silver containing layer(s) by adding doping agents, alloy additives or the like or even adding very thin metal or metal compound layers, as long as the properties of the silver containing layer(s) necessary to function as highly light-transmitting and low light-absorbent IR-reflective layer(s), are not substantially impaired thereby.

In an embodiment, the second coating comprises, in sequence from the second surface: a base layer adjacent to and in contact with the second surface; a first silver containing layer; and, an upper dielectric layer.

Such a layer sequence is typical of low-emissivity and/or infra-red reflecting coatings. In some embodiments, the base layer may comprise an oxide of zirconium and titanium ZrxTiyOz. Alternatively, the base layer may comprise a nitride, oxide or oxynitride of silicon and/or aluminium. Alternatively, the base layer may comprise an oxide of titanium.

In some embodiments the second coating may comprise a lower dielectric layer between the base layer and the first silver containing layer. Such a lower dielectric layer may be provided to improve the anti-reflection and/or colour performance of the layer, and may comprise oxides of zinc, oxides of tin, or mixed oxides of zinc and tin. In some embodiment the lower dielectric layer may be provided as a single layer, or alternatively as multiple sub-layers of the same or different composition or structure.

The lower dielectric layer may comprise one or more of growth promotion layers, stabilisation layers, separation layers and/or barrier layers as required for proper functioning of the coating.

In an embodiment, the second coating comprises a growth promotion layer in contact with the first silver layer between the first silver layer and the second surface, and preferably the growth promotion layer comprises an oxide of zinc, preferably the growth promotion layer further comprises aluminium. Such growth promotion layers have been shown to be particularly effective at forming a well orientated silver containing layer, which is associated with a reduction in sheet resistance and therefore an improvement in low- emissivity performance.

It is within the scope of this disclosure to apply the inventive concept to prepare low-emissivity and/or solar control coatings comprising two or more silver containing layers. When providing more than one silver containing layer, all of the silver containing layers are preferably spaced apart by intervening dielectric layers, referred to herein collectively as “central anti-reflection layers”, to form a Fabry-Perot interference filter, whereby the optical properties of the low emissivity and/or solar control coating may be further optimized for the respective application.

In an embodiment, each silver containing layer is spaced apart from an adjacent silver containing layer by an intervening central dielectric layer. The intervening central dielectric layer(s) may comprise a combination of one or more of the following layers: a layer based on an (oxi)nitride of silicon and/or an (oxi)nitride of aluminium; a layer based on an oxide of zinc and tin or an oxide of tin and a layer based on a metal oxide such as an oxide of zinc.

In some embodiments, the coating further comprises a second silver containing layer between the silver containing layer and the upper dielectric layer. Preferably, the coating further comprises a central dielectric layer between the silver containing layer and the second silver containing layer and/or a second barrier layer between the second silver containing layer and the upper dielectric layer.

In some embodiments, the coating further comprises a third silver containing layer between the second silver containing layer and the upper dielectric layer. Preferably, the coating further comprises a second central dielectric layer between the second silver containing layer and the third silver containing layer and/or a third barrier layer between the third silver containing layer and the upper dielectric layer.

In some embodiments, the coating further comprises a fourth silver containing layer between the third silver containing layer and the upper dielectric layer. Preferably, the coating further comprises a third central dielectric layer between the third silver containing layer and the fourth silver containing layer and/or a fourth barrier layer between the fourth silver containing layer and the upper dielectric layer.

In some cases, central dielectric layers may comprise a layer comprising an oxide of zirconium and titanium. In some embodiments, the layer comprising an oxide of zirconium and titanium ZrxTiyOz of a central dielectric layer may comprise an atomic proportion of Zr based on Zr and Ti, calculated as x/(x+y), from 0.40 to 0.95.

In some preferred embodiments each silver containing layer is spaced apart from another silver containing layer by an intervening central dielectric layer, wherein each central dielectric layer comprises at least, in sequence from the silver containing layer that is located nearest to the glass substrate, a layer based on an (oxi)nitride of silicon and/or an (oxi)nitride of aluminium; a layer based on an oxide of zinc and tin or an oxide of tin; and a layer based on a metal oxide such as an oxide of zinc.

Therefore, for coated glass panes comprising two or more silver based functional layers it is preferred if each silver containing layer is spaced apart from an adjacent silver containing layer by an intervening central dielectric layer, wherein each central dielectric layer comprises at least, in sequence from the silver containing layer that is located nearest to the glass substrate: a layer based on a mixed metal oxide comprising nickel and chromium; a layer based on a mixed metal oxide based on zinc and aluminium, a layer based on an (oxi)nitride of silicon and/or an (oxi)nitride of aluminium; a layer based on an oxide of tin preferably comprising zinc; and a layer based on a metal oxide such as an oxide of zinc.

Upper Dielectric Layer

Also in relation to the first aspect of the embodiments, the second coating may comprise an upper dielectric layer. The upper dielectric layer may comprise, from the uppermost silver containing layer: i) a layer based on an oxide of tin preferably comprising zinc, or a layer based on zinc preferably comprising aluminium, or a layer based on a nitride of tungsten; and/or ii) a layer based on an (oxi)nitride of silicon and/or an (oxi)nitride of aluminium, or a layer based on zinc preferably comprising aluminium.

Layers based on an oxide of tin may comprise zinc in the upper dielectric layer. These layers may have a thickness between 0.5 tand 5 nm, more preferably between 1 and 4 nm, even more preferably between 1.5 and 3 nm. These thicknesses enable further ease of deposition and improvement in optical characteristics such as haze whilst retaining mechanical durability.

Layers based on zinc preferably comprising aluminium in the upper dielectric layer may preferably have a thickness of from 0.5 to 5 nm, more preferably from 1 to 4 nm, even more preferably from 1.5 to 3 nm. These preferred thicknesses also enable further ease of deposition and improvement in optical characteristics such as haze whilst retaining mechanical durability.

Layers in the upper anti-reflection layer based on an (oxi)nitride of aluminium or an (oxi)nitride of silicon may preferably comprise a thickness of at least 5 nm; preferably from 5 to 50 nm; more preferably from 10 to 40 nm; even more preferably from 10 to 30 nm; most preferably from 15 to 30 nm. Such thicknesses provide further improvement in terms of mechanical robustness of the coated pane. Said layer based on an (oxi)nitride of aluminium, an (oxi)nitride of silicon, may preferably be in direct contact with a layer comprising on an oxide of zinc (Zn) in the upper dielectric layer.

Layers based on an (oxi)nitride of aluminium, and/or an (oxi)nitride of silicon, may comprise a major part of the upper anti-reflection layer and provide stability (better protection during heat treatments) and diffusion barrier properties. Said layer is preferably deposited as an Al nitride and/or Si nitride layer by reactive sputtering of a Si, Al or mixed SiAl target, for example, of a Si90A110 target in a N2 containing atmosphere. The composition of the layer based on an (oxi)nitride of aluminium and/or an (oxi)nitride of silicon may be essentially stoichiometric Si90AI10Nx. Preferably the layers in the upper dielectric layer are based on essentially stoichiometric metal oxides. The use of layers based on essentially stoichiometric metal oxides rather than metallic or less than 95% stoichiometric barrier layers leads to an extremely high optical stability of the coating during a heat treatment and effectively assists in keeping optical modifications during heat treatment small. Additionally, the use of layers based on essentially stoichiometric metal oxides provides benefits in terms of mechanical robustness.

To further optimize the optical properties of the coated pane the upper dielectric layer and/or central dielectric layer(s) may comprise further partial layers consisting of suitable materials generally known for dielectric layers of low-e and/or solar control coatings, in particular chosen from one or more of the oxides of Sn, Ti, Zn, Nb, Ce, Hf, Ta, Zr, Al and/or Si and/or of (oxi)nitrides of Si and/or Al or combinations thereof. When adding such further partial layers it should however be verified that the heat treatability aimed at herein is not impaired thereby.

In some cases, the upper dielectric layer may comprise a layer comprising an oxide of zirconium and titanium ZrxTiyOz. In some embodiments, the layer comprising an oxide of zirconium and titanium ZrxTiyOz of the upper dielectric may comprise an atomic proportion of Zr based on Zr and Ti, calculated as x/(x+y), from 0.40 to 0.95.

Growth Promotion Layer

In an embodiment, the coating further may comprise a growth promotion layer between the base layer and the silver containing layer. The growth promotion layer functions as a growth promoting layer for a subsequently deposited silver containing layer. In an embodiment, the silver containing layer nay be in direct contact with the growth promotion layer. In a further embodiment, the base layer may be the growth promotion layer, wherein the growth protection layer is in direct contact with the substrate.

In some embodiments, the growth promotion layer may be in direct contact with the base layer and the silver layer, such that no stabilisation layer is present between them. Preferably, where the growth promotion layer is in direct contact with the base layer the base layer has a thickness in nm of from 10 to 60.

In an embodiment, the growth promotion layer may be based on an oxide of zinc. Zinc oxide and mixed zinc oxides are effective growth promoting layers and thereby assist in achieving a low sheet resistance at a given thickness of the subsequently deposited silver containing layer. The growth promotion layer based on an oxide of zinc is optionally mixed with metals such as aluminium or tin in an amount of up to about 10 weight % (weight % referring to the target metal content). A typical content of said metals such as aluminium or tin is about 2 weight %, aluminium being actually preferred.

The growth promotion layer may be based on an oxide of zinc of the lower dielectric layer is reactively sputtered from a zinc target in an atmosphere comprising oxygen (02), or deposited by sputtering from a ceramic target, for example based on zinc oxide and optionally doped with aluminium, in an atmosphere containing zero or only a small amount, that is, generally no more than about 5 volume %, of oxygen.

In an embodiment, the growth promotion layer may have a thickness of at least 2 nm. In another embodiment, the growth promotion layer may have a thickness of from 2 to 15 nm; or from 3 to 12 nm. In yet another embodiment, the growth promotion layer may have a thickness of from 4 to 10 nm. Most preferably the growth layer has a thickness of from 5 to 8 nm. Stabilisation Layer

In an embodiment, the coating further comprises a stabilisation layer between the base layer and the growth promotion layer. Preferably the stabilisation layer is in direct contact with the base layer and/or comprises (Zn)SnOx.

The stabilisation layer is thought to improve stability during a heat treatment by providing a dense and thermally stable layer, and contributing to reduce the haze after a heat treatment.

In an embodiment, the stabilisation layer comprises tin oxide, preferably comprising zinc, (Zn)SnOx. As used herein, a layer comprising (Zn)SnOx may comprise either tin oxide, SnOx, or zinc tin oxide, ZnSnOx.

When the stabilisation layer comprises zinc tin oxide, the stabilisation layer may comprise, in weight % of the total metal content of the layer: from 10 to 90 weight % zinc and from 90 to 10 weight % tin; more preferably from 40 to 60 weight % zinc and from 40 to 60 weight % tin; even more preferably around 50 weight % each of zinc and tin. In some preferred embodiments the stabilisation layer comprising zinc tin oxide comprises at most 18 weight % tin, more preferably at most 15 weight % tin, even more preferably at most 10 weight % tin. The stabilisation layer comprising zinc tin oxide is preferably deposited by reactive sputtering of a mixed ZnSn target in the presence of O2.

The stabilisation layer preferably has a thickness of at least 0.5 nm. In an embodimentthe stabilisation layer may have a thickness of from: 0.5 to 15 nm; or 0.5 to 13 nm; or 1 to 12 nm. In addition, the stabilisation layer may have a thickness of from: 1 to 7 nm; or 2 to 6 nm; or 3 to 6 nm. Most preferably the stabilisation layer comprises zinc tin oxide and has a thickness of from 3 to 5 nm for a coated glass pane with layer sequence comprising a single silver containing layer. An upper thickness limit in the region of 8 nm is preferred due to optical interference conditions and by a reduction of heat treatability due to the resulting reduction in the thickness of the base layer that would be needed to maintain the optical interference boundary conditions for anti-reflecting the functional layer.

In an alternative embodiment in relation to the first aspect of the present invention, when the coated glass pane comprises more than one silver containing layer, the stabilisation layer preferably has a thickness of at least 10 nm. More preferably, the stabilisation layer has a thickness of from 10 nm to 20 nm. Even more preferably, the stabilisation layer has a thickness of from 12 nm to 16 nm. Most preferably, the stabilisation layer comprises zinc tin oxide and has a thickness of from 12nm to 14nm. Separation Layer

In some embodiments, the coating further comprises a separation layer between the stabilisation layer and the growth promotion layer. Preferably, the separation layer is in direct contact with the stabilisation layer and/or comprises a metal oxide and/or an (oxi)nitride of silicon and/or an (oxi)nitride of aluminium and/or alloys thereof.

When the coating sequence comprises more than one silver-based coating layer, the lower dielectric layer preferably consists of, in sequence from the glass substrate: a stabilisation layer; and a growth promotion layer. However, when the coating sequence comprises only a single silver-based coating layer the lower dielectric layer may additionally comprise a separation layer between the stabilisation layer and the growth promotion layer.

The separation layer may preferably be based on a metal oxide and/or an (oxi)nitride of silicon and/or an (oxi)nitride of aluminium and/or alloys thereof.

The term “(oxi)nitride of silicon” encompasses both silicon (Si) nitride (SiNx) and silicon (Si) oxinitride (SiOxNy), whilst the term “(oxi)nitride of aluminium” encompasses both aluminium (Al) nitride (AINx) and aluminium (Al) oxinitride (AIOxNy). Silicon (Si) nitride, silicon (Si) oxinitride, aluminium (Al) nitride and aluminium (Al) oxinitride layers are preferably essentially stoichiometric (for example, in silicon nitride = Si3N4, the value of x in SiNx = 1.33) but may also be substoichiometric or even super-stoichiometric, as long as the heat treatability of the coating is not negatively affected thereby. One preferred composition of the base layer based on an (oxi)nitride of silicon and/or an (oxi)nitride of aluminium of the lower dielectric layer is an essentially stoichiometric mixed nitride Si90AI10Nx.

Layers of an (oxi)nitride of silicon and/or an (oxi)nitride of aluminium may be reactively sputtered from silicon (Si-) and/or aluminium (Al)-based targets respectively in a sputtering atmosphere containing nitrogen and argon. An oxygen content of the layer based on an (oxi)nitride of silicon and/or an (oxi)nitride of aluminium may result from residual oxygen in the sputtering atmosphere or from a controlled content of added oxygen in said atmosphere. It is generally preferred if the oxygen content of the silicon (oxi)nitride and/or aluminium (oxi)nitride is significantly lower than its nitrogen content, that is, if the atomic ratio O/N in the layer is kept significantly below 1. It is most preferred to use silicon nitride and/or aluminium nitride with negligible oxygen content. This feature may be controlled by making sure that the refractive index of the layer does not differ significantly from the refractive index of an oxygen-free Si nitride and/or aluminium nitride layer.

It is within the scope of this disclosure to use mixed silicon (Si) and/or aluminium (Al) targets or to otherwise add metals or semiconductors to the silicon (Si) and/or aluminium (Al) component of this layer as long as the essential barrier and protection property of the layer is not lost. For example, the aluminium (Al) with silicon (Si) targets may be mixed, other mixed targets not being excluded. Additional components may be typically present in amounts of from 10 to 15 weight %. Aluminium is usually present in mixed silicon targets in an amount of 10 weight %.

In addition, the separation layer may preferably have a thickness of at least 0.5 nm; or preferably from 0.5 to 6 nm; more preferably from 0.5 to 5 nm; even more preferably from 0.5 to 4 nm; most preferably from 0.5 to 3 nm. These preferred thicknesses enable further improvement in haze upon heat treatment. The separation layer preferably provides protection during the deposition process and during a subsequent heat treatment. The separation layer is preferably either essentially fully oxidised immediately after deposition, or it oxidizes to an essentially fully oxidized layer during deposition of a subsequent oxide layer.

When the separation layer is based on a metal oxide said separation layer may preferably comprise a layer based on an oxide of: Ti, Zn, NiCr, InSn, Zr, Al and/or Si.

When the separation layer is preferably based on a metal oxide, it may be deposited using non-reactive sputtering from a ceramic target based on for example a slightly substoichiometric titanium oxide, for example a TiO1.98 target, as an essentially stoichiometric or as a slightly substoichiometric oxide, by reactive sputtering of a target based on Ti in the presence of 02, or by depositing a thin layer based on Ti which is then oxidised. In the context of the present invention, an “essentially stoichiometric oxide” means an oxide that is at least 95% but at most 100% stoichiometric, whilst a “slightly substoichiometric oxide” means an oxide that is at least 95% but less than 100% stoichiometric.

In addition to the metal oxide and/or (oxi)nitride of silicon and/or (oxi)nitride of aluminium and/or alloys thereof upon which it is based, the separation layer may further include one or more other chemical elements chosen from at least one of the following elements: Ti, V, Mn, Co, Cu, Zn, Zr, Hf, Al, Nb, Ni, Cr, Mo, Ta, Si, or from an alloy based on at least one of these materials, used for instance as dopants or alloyants.

In an, the separation layer based on a metal oxide and/or (oxi)nitride of silicon and/or (oxi)nitride of aluminium does not include one or more other chemical elements.

In one embodiment, the separation layer may be based on a metal oxide, which comprises an oxide of zinc (Zn) and/or an oxide of titanium.

In another embodiment of the present invention, the separation layer may be based on a metal oxide, which comprises an oxide of titanium.

In an embodiment, the separation layer is based on an oxide of titanium when the layer sequence of the coated glass comprises one silver containing layer.

Whilst the separation layer may also be based on an oxide of titanium when the layer sequence comprises more than one silver containing layer, it may also be preferred that when the layer sequence or stack comprises more than one silver containing layer that the layer sequence does not comprise a separation layer in the lower dielectric layer.

In addition, it is preferred that when the separation layer is based on a metal oxide and that the metal oxide is based on titanium oxide, that the titanium oxide has a preferred thickness of from 0.5 to 3nm.

Therefore, when the coating sequence comprises only a single silver-based coating layer the lower dielectric layer may consist of, in sequence from the glass substrate: a zinc tin oxide layer in direct contact with the base layer; a separation layer in direct contact with the zinc tin oxide layer; and a zinc oxide layer in direct contact with the separation layer.

Alternatively, when the coating sequence comprises more than one silverbased layer, the lower dielectric layer may consist of, in sequence from the glass substrate: a zinc tin oxide layer in direct contact with the base layer; and a zinc oxide layer in direct contact with the zinc tin oxide layer.

In a further embodiment, when the coating sequence comprises more than one silver-based layer, the growth promotion layer of preferably an oxide zinc may be in contact with the base layer and the silver-based layer. In this case, the zirconium titanium oxide base layer may be of increased thickness. Alternatively, when the coating sequence comprises more than one silver-based layer coating the coating sequence may comprise a zirconium titanium oxide base layer and a further zirconium titanium oxide stabilisation layer in contact with the base layer, and a zinc oxide layer in contact with the stabilisation layer. In this embodiment, the zinc tin oxide layer is not required in the lower dielectric layer, leading to a simpler coating structure.

Barrier Layer

In an embodiment, the coating further comprises a barrier layer between the silver containing layer and the upper dielectric layer. Preferably, the barrier layer is in direct contact with the silver containing layer.

In an embodiment, where the coating comprises multiple silver containing layers, each silver containing layer is in direct contact with an overlying barrier layer. At least a portion of the barrier layer that is in direct contact with the silver containing layer is preferably deposited using non-reactive sputtering to avoid silver damage. It has been found that a superior protection of the silver containing layer during the deposition process and a high optical stability during a heat treatment may be achieved if the barrier layer comprises a layer of a mixed metal oxide sputtered from a mixed metal oxide target.

In some embodiments, the barrier layer comprises a layer based on an oxide of zinc. When the barrier layer comprises a layer based on an oxide of zinc, said oxide may be a mixed metal oxide such as ZnO:AI. Good results are particularly achieved if a layer based on ZnO:AI is sputtered from a conductive ZnO:AI target. ZnO:AI may be deposited fully oxidized or such that it is slightly suboxidic.

The barrier layer may comprise a layer based on an oxide of zinc with a thickness of: at least 0.5 nm, more preferably, the barrier layer comprises a layer based on an oxide of zinc with a thickness of from 0.5 to 10 nm. Most preferably the barrier layer comprises a layer based on an oxide of zinc with a thickness of from 1 to 10 nm. In addition, it is possible when the barrier layer comprises a layer based on an oxide of zinc for the barrier to actually comprise a number of zinc oxide layers such as layers based not only on a mixed metal oxide such as ZnO:AI, but also on an oxide of zinc and tin. Suitable barrier layers may therefore be in the form of three layers, in sequence from the glass substrate: ZnO:AI, ZnSnOx, ZnO:AI. Such triple barrier arrangements may have a combined thickness of between 3 and 12nm.

Further triple barrier arrangements may preferably be selected from the group consisting of the following combinations of layers in sequence from the silver containing layer: ZnO:AI/TiOx/ZnO:AI, ZnO:AI/ZnSnOx/ZnO:AI, TiOx/ZnSnOx/ZnO:AI, TiOx/ZnO:AI/TiOx, TiOx/ZnSnOx/TiOx, and ZnO:AI/ZnSnOx/TiOx.

Alternatively, the barrier layer may comprise a layer based on a mixed metal oxide based on nickel and chromium, such as a layer of NiCrOx. It has further been found that suitable protection of the silver containing layer during the deposition process and a high optical stability during heat treatment may be achieved if the barrier layer comprises a mixed metal oxide based on nickel and chromium, such as a layer of NiCrOx. This is especially the case when the coated glass pane comprises two or more silver containing layers. However, the layer of NiCrOx may also be used when the coated glass pane comprises a single silver containing layer. Preferably, the layer of NiCrOx is deposited as substoichiometric NiCrOx.

As such, in some embodiments, the barrier layer may preferably comprise a layer based on a mixed metal oxide based on nickel and chromium with a thickness of at least 0.5 nm, more preferably, the barrier layer comprises a layer based on a mixed metal oxide based on nickel and chromium with a thickness of from 0.5 to 10 nm. Most preferably the barrier layer comprises a layer based on a mixed metal oxide based on nickel and chromium with a thickness of from 1 to 10 nm.

Protective Layer

The coated glass pane further may comprise a protective layer that is the outermost layer of the coating, for increased mechanical and/or chemical robustness, for example scratch resistance. In an embodiment, the protection layer may comprise a layer based on an oxide of zinc and tin. In addition to zinc and tin, the protection layer may contain zirconium. In an embodiment, a layer may be based on an oxide of zinc, tin and zirconium comprises from 12 to 35 atomic % zirconium. In an embodiment, the layer may be based on an oxide of zinc, tin and zirconium comprises from 15 to 33 atomic % zirconium. In yet another embodiment, the layer based on an oxide of zinc, tin and zirconium comprises from 18 to 33 atomic % zirconium.

Light absorbing layer

It is often desirable for panes in architectural glazings to have a visible light transmission that is less than 90%, preferably from 50 to 70%. This reduces glare, which is often unpleasant for the consumer. However, in order to promote luminescent edge emission, it is desirable that the sheet of transparent material of the inventive substrate has a high visible light transmission, preferably greater than 90%. These two requirements are in direct conflict.

The inventors have discovered that by providing a second coating with a light absorbing layer, a sheet of transparent material with high visible light transmission with high visible light transmission, even in excess of 90%, may be used, while the coated substrate has a visible light transmission of less than 90%, preferably from 50 to 70%. A light absorbing layer is defined herein as a coating layer that causes a reduction in visible light transmission of at least 10%, preferably at least 20%.

Transparent sheet of glazing material

In an embodiment, the transparent sheet of glazing material has a visible light transparency of 5% or greater, preferably from 50 to 99%. Such visible light transparencies allow the internal reflection of photons towards the substrate edges. It is preferred that the visible light transparency is high, preferably at least 80%, even more preferably at least 90% so that only a minority of photons are absorbed by the sheet of glazing material.

In an embodiment, the transparent sheet of glazing material comprises glass, preferably soda-lime silica glass. Soda-lime silica glass is widely available and cost effective.

In an embodiment, the transparent sheet of glazing material comprises low- iron soda-lime silica glass. A low-iron soda-lime silica glass preferably comprises 1 weight % or less iron. More preferably the low-iron soda-lime silica glass comprises 0.1 weight % or less iron. Most preferably, the low-iron soda-lime silica glass comprises 0.03 weight % or less iron. An example of a suitable low-iron soda-lime-silica glass for use in accordance with the first aspect of the present invention is Pilkington OptiwhiteTM, available from Nippon Sheet Glass Co., Ltd. A low-iron soda-lime silica glass is of particular benefit, as such glasses are associated with high visible light transparency, thereby reducing the proportion of luminesced photons absorbed by the transparent material and thereby increasing the edge emission of the luminescent substrate.

In an embodiment, the transparent sheet of glazing material comprises heat treated glass. As used herein, a treatment wherein a glass pane is subjected to a temperature of greater than or equal to 500 °C for at least 1 minute, preferably wherein a glass pane is subjected to a temperature of greater than or equal to 600 °C for at least 3 minutes is considered to be a heat treatment, and as such the glass is heat treated. A heat treated glass may be identified by the presence of bends and or dicing upon breakage.

In an embodiment, the substrate comprises glass of thickness from 3 to 15 mm, more preferably from 4 to 12 mm, yet more preferably 5 to 10 mm, most preferably glass of thickness from 7 to 9 mm. Such glass thicknesses are of particular benefit, as they may be easily incorporated into glazings, while maintaining a low path length for luminesced photons passing through the sheet of glazing material to an edge.

The invention will be further illustrated with reference to the attached drawings, which schematically will show embodiments according to the invention. It will be understood that the invention is not in any way restricted to these specific embodiments.

Brief description of the embodiments

Fig. 1 depicts a luminescent coated glazing unit used in the luminescent solar concentrator structures and glazing unit structures described with reference to the embodients .

Fig. 2 depicts an apparatus for measuring the luminescence of coatings;

Fig. 3 depicts a schematic cross-sections of luminescent solar concentrator devices according to an embodiment.

Fig. 4 depicts a schematic cross-sections of luminescent solar concentrator devices according to an embodiment.

Fig. 5 depicts a schematic cross-sections of luminescent solar concentrator devices according to an embodiment.

Fig. 6 depicts a glazing according to an embodiment.

Fig. 7A and 7B depict a modelled transmission spectrum and reflectance spectrum of a reflecting coating according to an embodiment.

Description of the embodiments Fig. 1 depicts a luminescent coated glass pane 100 that is used in the luminescent solar concentrator structures and glazing unit structures described with reference to the embodients. As shown in the figure, the coated glass pane comprises a transparent sheet of glazing material 102 with a first surface 104i , a second surface 1042 opposite the first surface, and an edge surface 104s. A first coating 106 comprising a least one luminescent layer may be provided over (at least part of) the first surface and a second coating 108 comprising at least one silver containing layer may be provided over at least part of the second surface.

Fig. 2 depicts an apparatus for measuring the luminescence of coatings. The edge detection apparatus 200 comprises a sample 202 resting on stand-offs 206, within a testing area defined by location pins 204. Below the stand-offs and underneath the whole sample is a piece of black card 208. The glass sample is mounted on the stand-offs such that a surface comprising a luminescent coating layer (not shown) is orientated away from the black card. A photon receiver 210 comprising a cosine corrector is mounted on a bracket- and aligned with and in contact with an edge of the glass sample. The photon receiver is connected to a UV filter 212 via an optical fibre 214 and then to a photon counter 216 via the optical fibre.

A black painted box 218 is placed over the sample, and repeatable positioning is ensured by the location pins. A UV 365 nm led lamp 220 is mounted in the black painted box 9 aligned with the centre of the glass sample. The UV led lamp and photon counter are powered by electrical supplies and the photon counter is connected to a computer. During the measurement, the UV led lamp illuminates the glass sample, causing the luminescent coating layer to luminesce. Photons are internally reflected to the glass substrate edges, and some enter the photon receiver, and are passed through a UV filter for removing unabsorbed UV light before being transferred to the photon counter which then communicates with the computer to produce spectra.

Measured spectra were integrated to provide a photon count over the luminescent range of the luminescent coating in question.

For the SiSmAION layers integration was carried out between 660 and 750 nm, and it was seen that the luminescent emission increased linearly with increasing thickness of luminescent coating for a given composition. Therefore, the photon count may be divided by the thickness in nm to provide a value of counts per nm which may then be compared between samples if desired. Thickness was measured using a Dektak stylus profilometer.

Hereunder aspects of the embodimensts are described by way of non-limiting examples. Luminescent layers for comparative examples may be produced as follows. Clear float glass substrates of 6 mm thickness - Pilkington Optiwhite™ available from NSG, UK - were prepared by washing and then submitted to a sputtering process to provide a luminescent layer on the air side of the float glass from a target comprising SiAISm (Si 89.35wt% I Sm 3.14wt% I Al 7.51wt%). Sputtering of the luminescent layer was carried out in a pilot-scale Von Ardenne coater using a standard dual magnetron target with a MFG power supply (Huttinger Tig 50) and a power of 15 kW. In an embodiment, sputtering target may comprise between 85 and 95 wt% silicon, between 5 and 10 wt% aluminium, and between 2 and 4 wt% samarium. In a further embodiment, the sputtering targe target may comprise between 88 and 90 wt% silicon, between 7 and 8 wt% aluminium, and between 3 and 4 wt% samarium.

The proportions of gases in a sputtering atmosphere is conventionally controlled by the flow rates of the input gases, in these experiments when depositing the luminescent coating the atmosphere was formed from argon (250 seem) oxygen (varied due to voltage control around a target of 90 seem) and nitrogen (15 seem) in all experiments. The substrate was passed under the target at a speed of 600 mm/min. Each SiSmAION layer was approximately 2500 nm in thickness. In an embodiment, the sputtering atmosphere comprises an atmosphere comprising a noble gas, oxygen and nitrogen, wherein sputtering atmosphere comprises a percentage of nitrogen based on nitrogen and oxygen from 1 to 90% by volume, preferably from 5 to 70%, more preferably of from 10 to 50%, even more preferably of from 12 to 30%, by volume.

After deposition of the first coating comprising a luminescent layer, the substrate was heat treated at 600 °C for at least 3 minutes, then the luminescent edge emission of the sample measured using the apparatus as depicted in Figure 2, to provide a control measurement. While in these examples a heat treatment is carried out prior to deposition of the second coating, which may be a low-emissivity and/or infra-red reflecting coating, this is done primarily to allow the control measurement to be taken such that different coatings to be evaluated. It is within the scope of the invention that the first coating and the second coating are deposited prior to any heat treatment of the substrate. As such, it is preferable that the second coating is a “heat treatable” coating.

Coated glass panes may also be submitted to strengthening and bending processes, known as heat treatments. As used herein, a treatment wherein a glass pane is subjected to a temperature of greater than or equal to 500 °C for at least 1 minute, preferably wherein a glass pane is subjected to a temperature of greater than or equal to 600 °C for at least 3 minutes is considered to be a heat treatment, and as such the glass is heat treated. A heat treated glass may be identified by the presence of bends and or dicing upon breakage. However, coated glass panes are often incompatible with heat treatments, and may be damaged by the process. Typical damage to coated glass panes caused by heat treatments may be indicated by increased haze (often perceived as cloudiness), pinholes and spots.

The function of the glazing may also be impaired, resulting in a decrease in light transmission and/or a reduction in the effectiveness of the low-emissivity coating, exemplified by an increase in sheet resistance values. As such, a coated glass pane that is damaged by heat treatment may be unacceptable due to its appearance and/or its reduced functional ability. A coated glass pane that exhibits such damage upon heat treatment is known as “non-heat treatable”. Conversely, a coated glass pane is deemed to be “heat treatable” if it survives a heat treatment without significant damage.

After the control measurement, a series of examples and comparative examples were prepared whereby further coating layers were applied to the substrate coating. Further coating layers for comparative examples and examples were produced by sputtering on in a pilot-scale Von Ardenne coater with a MFG power supply (Huttinger Tig 50). Layers comprising silver (Ag), and zinc aluminium oxide (ZAO), were deposited.

Layers of zinc aluminium oxide (also referred to as ZAO), were sputtered from conductive ZnOx:AI targets comprising ZnO 97% with 3% AI2O3 by weight in a pure Argon (Ar) sputter atmosphere with less than 5% oxygen using 300 W power, layers of silver were deposited from silver metal targets in a pure Argon (Ar) atmosphere with less than 5% oxygen using 300 W power.

After deposition of the further coating layers, the luminescent edge emission of the samples was measured to provide, and the % increase calculated as follows:

[LEE % increase] = LEE _in itiai LEEfinai ^x 100 where LEEmitiai is the luminescent edge emission before application of the second coating and LEEfinai is the luminescent edge emission after application of the second coating.

The potential for such coatings to be used in glazings was assessed by measuring their visible light transmission (Tvis) and low-e properties. A comparison between examples and comparative examples wherein the coatings are varied is depicted in Table 1 wherein the thicknesses of the layers in nm are shown in brackets.

Table 1

It was not possible to measure the emissivity of example 3 due to the extremely high reflectance of the silver mirror surface. Example 2 provided a measured sheet resistance of 3.63 ohm/square.

As shown by comparative example 1 (CE1), the addition of a low-emissivity coating upon the same substrate surface on a luminescent coating causes a marked decrease in the luminescence edge emission. However, as shown by example 2, the same low-emissivity coating on the substrate surface opposite that of the luminescent coating greatly improves the luminescent edge emission.

The results show that the structure of the low-emissivity coating in example 2 of dielectric/functional layer/dielectric is highly beneficial in improving the luminescent edge emission: when the same silver thickness is used without dielectric layers as in example 1 a slight reduction in luminescent edge emission is seen, while when the dielectric layers are used without the silver layer as in comparative example 2 a marked reduction in luminescent edge emission is seen. While example 1 has a slight reduction in luminescent edge emission, it may still provide benefits in IR radiation reflection, improving the overall performance of the glazing. However, in most cases a dielectric/functional layer/dielectric type low-emissivity coating such as example 2 will be preferred. However, where the transmission of visible light is of lower priority, a thicker silver layer may be employed, as in example 3. Such a thick silver layer greatly enhances the luminescent edge emission of the substrate. Accordingly, the visible light transmission, IR radiation reflection, and luminescent edge emission of a substrate may be adjusted to provide the desired compromise.

Since pure ZAO has a higher refractive index, >1.7 and Ag has a very low refractive index, <0.2, across the whole VIS-NIR range, see e.g. P. B. Johnson and R. W. Christy. Optical constants of the noble metals, Phys. Rev. B 6, 4370-4379 (1972) and O. Aguilar, et al. Optoelectronic characterization of Zn1-xCdxO thin films as an alternative to photonic crystals in organic solar cells, Opt. Mater. Express 9, 3638-3648 (2019). The loss reduction in LEE due to the highly reflective properties observed by example 2 at table 2 may be extrapolated to any luminescent layer with emission in that range.

The transmission spectrum of the reflecting coating of example 2 on iron-free glass was modelled and is depicted in Fig. 7A. Modelling was carried out without the presence of the luminescent coating to provide the properties of the reflection coating alone. As shown by Fig. 7A, the transmission of Example 2 shows a maximum at 560 nm, which is in the middle of the visible spectrum, and therefore does not produce a red transmission colour which is generally undesirable. Similarly, the modelled transmission colour coordinates are a*=-2.17 and b*=5.17. These correspond to a neutral, slightly green colour which is much more acceptable than red colours caused by a positive a* value. As such, preferably the reflection coatings as discussed herein provide transmission LAB values such that -10<a*<10 and -10<b*<10, more preferably -5<a*<0 and -10<b*<10.

The glass-side reflection spectrum of the reflecting coating of Example 2 on iron-free glass was modelled and is depicted in Fig. 7B. Modelling was carried out without the presence of the luminescent coating to provide the properties of the reflection coating alone. The reflection was modelled with the observer on the glass side, to provide an indication of the reflection capability of the reflecting coating for a luminescent coating on the reverse side of the substrate. As shown by Fig. 7B, the reflecting coating of Example 2 comprises a local reflection minimum at 600 nm. This provides a visible colour reflection that is neutral, and not noticeably red, which is therefore more acceptable when used in installations. The modelled reflection colour coordinates a*=0.24 and b*=-19.23. While a positive a* value is present in this example, it is not sufficiently positive to cause the overall impression to be an undesirable red color, while the more strongly negative b* value causes a more highly desirable blue colour in reflection. As such, preferably the reflection coatings as discussed herein provide reflection LAB values such that -10<a*<10 and -20<b*<10, more preferably -5<a*<0 and -20<b*<10.

As shown by Fig. 7B, the reflection spectrum of Example 2 rises steeply above 600 nm, and is therefore particularly well suited to reflecting the emission peak at between 650 and 800 nm of a luminescent layer comprising Sm ²⁺ .

As such, in agreement with the invention, there is provided a reflecting coating that is adapted to reflect the emission of a luminescent layer comprising Sm ²⁺ comprising: a first dielectric layer of optical thickness from 20 to 40 nm, preferably from 25 to 35 nm; a first silver containing layer of physical thickness from 12 to 18 nm, preferably from 14 to 16 nm; and, a second dielectric layer of optical thickness from 70 to 150 nm, preferably from 100 to 120 nm. Not only is this reflecting coating well suited to reflecting luminescent photons produced by Sm ²⁺ containing layers, but it also has very beneficial transmission and reflection colours, which allow such a coating to be used in a wide variety of installations.

In an embodiment, in the reflecting coating that is adapted to reflect the emission of a luminescent layer comprising Sm ²⁺ , the first dielectric layer may comprise a layer of zinc oxide which, optionally, may be doped with aluminium and the second dielectric layer comprises a layer of zinc oxide which, optionally, may be doped with aluminium.

The skilled person will appreciate that the optional features of the invention may be combined with the reflecting coating adapted to reflect the emission of a luminescent layer comprising Sm ²⁺ as required.

As shown by Fig. 7B, the reflection spectrum of Example 2 remains high in the 1150 to 1250 nm region, and is therefore not only well suited to the reflection of luminescent photons produced by Sm ²⁺ containing layers, but also particularly well suited to reflecting the emission of a luminescent layer comprising Tm ²⁺ and/or Mn ⁵⁺ , while still maintaining very beneficial transmission and reflection colours, which allow such a coating to be used in a wide variety of installations.

As such, in agreement with the invention, there is provided a reflecting coating that is adapted to reflect the emission of a luminescent layer comprising Sm ²⁺ and/or Tm ²⁺ and/or Mn ⁵⁺ comprising: a first dielectric layer of optical thickness from 20 to 40 nm, preferably from 25 to 35 nm; a first silver containing layer of physical thickness from 12 to 18 nm, preferably from 14 to 16 nm; and a second dielectric layer of optical thickness from 70 to 150 nm, preferably from 100 to 120 nm.

The skilled person will appreciate that the optional features of the invention may be combined with the reflecting coating adapted to reflect the emission of a luminescent layer comprising Sm ²⁺ and/or T m ²⁺ and/or Mn ⁵⁺ as required.

While the present embodiments comprise a first coating comprising a luminescent layer applied to the “air-side” of a float glass sheet and a second coating comprising a silver containing layer applied to the “tin-side” of a float glass sheet, the invention is not limited to such an arrangement. Where a float glass sheet is used, the first coating comprising a luminescent layer may be applied to the “tin-side” of the float glass sheet and a second coating comprising a silver containing layer applied to the “air-side” of the float glass sheet. Alternatively, other substrates not formed by the float process may be used, such as down-draw type glasses, where neither surface comes into contact with a layer of molten tin.

However, it is believed that the molten tin may interact with the surface of a soda-lime silica glass by depleting the sodium proportion in the surface region, and additionally providing some incorporation of tin. Both of these processes serve to potentially reduce the proportion of sodium which might migrate into the silver containing layer, especially during a heat treatment process, thereby reducing its low-emissivity performance. As such, it is preferred that when the luminescent coated substate comprises a transparent sheet of float glass, the first surface comprising a first coating comprising a luminescent layer is the “air-side” surface and the second surface comprising a second coating comprising a first silver containing layer is the “tin-side” surface.

XPS depth profiling of examples measured before and after heat treatment indicated that heat treatment had no significant effect on the composition of the luminescent layer, other than some migration of sodium from the glass substrate into the lowermost area of the luminescent layer. Heat treatment may improve the luminescence by altering the distribution within the amorphous layer, rather than its composition.

The Sm ²⁺ doped SiAION materials absorb a substantial part of the UV band and part of the visible band of the solar spectrum and convert radiation in these bands to radiation of a longer wavelength, in particular radiation in the red band between 650 nm and 800 nm. The SiAION host material exhibits superior properties in terms of mechanical strength, chemical inertness and thermal resistance and is for that reason used in protection and anti-reflection coatings in the glass industry. In particular, the Sm ²⁺ doped SiAION material forms a very stable conversion material that is fully compatible with standard production processes of the glass industry. In some embodiments, the Sm ²⁺ doped SiAION material may be used to form scatter-free amorphous Sm ²⁺ doped SiAION thin-film layers. The use of a low-scattering amorphous SiAION thin-film layer in a solar conversion device will ensure that the luminescent light does not escape the conversion device by scattering.

The material may be deposited using a sputtering technique, preferably a reactive magnetron sputtering technique, based on the elements Al, Si, O and N (SiAION) doped with Sm ²⁺ for converting solar radiation of at least part of the UV and/or visible spectrum into longer wavelength radiation.

In an embodiment, the lumiscent layer may be a particle-based coating. In an embodiment, the luminescent layer may include nanoparticles and/or microparticles embedded in a transparent matrix material. In an embodiment, nanoparticles and/or microparticles of a SIAION:Sm ²⁺ material may be synthesized using e.g. a sol-gel method including compounds such as Si(OC2Hs)4, AI(NOs)3 and samarium salts. Optionally, ethanol and/or citric acid may be added to assist the formation of the particles. Nitridation can be promoted by a nitrogen-filled sintering environment. A polymeric coating and/or lamination may be realized by embedding the particles in a suitable (organic) matrix material. Selection and optimization of polymer matrix material may be based on their applications and conditions. Epoxy resin, poly(methyl methacrylate), poly(siloxane), polycarbonate, polyurethane, polyvinyl butyral, ethylene-vinyl acetate, etc. are some common materials that can be used as a matrix material for these particles.

While the presented examples relate to luminescent layers comprising SiSmAION with a luminescent peak between 660 and 800 nm, the embodiments are not limited thereto. The skilled person will appreciate that on the basis of the present disclosure further silver containing coatings may be provided that are adapted to reflect alternative luminescent peak wavelengths.

For example, pentavalent manganese (Mn ⁵⁺⁾ doped inorganic luminescent materials and/or divalent thulium (Tm ²⁺ ) have properties that are particular suitable for application in solar conversion devices: improved luminescent, optical and/or material properties when compared to conventional inorganic phosphors that are used in LSC’s. Mn ⁵⁺ doped inorganic materials may absorb a substantial part of the UV band and visible band of the solar spectrum (around 50% of the power from the sun or more) and convert this to radiation of a higher wavelength, preferably a wavelength in the (near) infrared band. In some embodiments, the infrared emission may have a sharp peak in the infra-red band between 1150 and 1250 nm, preferably around 1190 nm. Furthermore, manganese is amongst twelve most abundant elements on Earth and has a relatively low price.

In a further embodiment, a luminescent Tm ²⁺ doped SiAION material, preferably an amorphous Tm ²⁺ doped SiAION material, may be used in a solar conversion device. This material, which absorbs a substantial part of the UV band and the visible band of the solar spectrum and converts this radiation in these bands to radiation in the nearinfrared band of the spectrum, exhibits excellent optical properties, in particular a low haze. Luminescent Tm ²⁺ doped SiAION material may exhibit emission in the near-infrared band, including a sharp emission peak around 1140 nm. This material exhibits broadband absorption of radiation in the solar spectrum, does not have self-absorption and advantageous material properties such as low-haze and processing compatibility with processes in the glass industry

Different synthesis processes may be used to form the Sm ²⁺ doped SiAION materials. The luminescent SiAION material may be produced as a Sm ²⁺ doped luminescent inorganic thin-film layer or as Sm ²⁺ doped SiAION particles (either nanoparticles or microparticles). These processes may include deposition methods that are compatible with conventional semiconductor processing methods so that the formation of a Sm ²⁺ doped inorganic luminescent material can be easily integrated in a production process of thin-film photovoltaic devices or solar conversion devices.

In an embodiment, a sputtering method may be used for producing an amorphous Sm ²⁺ doped SiAION thin film. The Sm ²⁺ doped SiAION thin films can be deposited on various substrates (e.g. float glass, quartz glass, borosilicate glass, low-iron glass, etc.) using a (magnetron) sputtering system wherein the substrate is kept at room temperature or at an elevated temperature (i.e. between room temperature and 600 °C for glass or between room temperature and 1000 °C for quartz. An exemplary synthesis method for producing an amorphous Sm ²⁺ doped SiAION thin film may include the following steps:

- clean a borosilicate glass substrate in an ultrasonic cleaner with soap solution and subsequently rinsed with acetone, ethanol and DI water;

- magnetron sputter deposition of SiAION:Sm ²⁺ using either separate Al, Si, and Sm targets or a combined Al-Si-Sm target (for example Si 96 at.%, Al 1.25 at.% and Sm 2.75 at.%; or a combination of: 90 at.%/10at.% Si/Sm compound target, 90at.%/10at.% Si/AI compound target and a pure Si target);

- during sputtering, the process gas flow may consist of a mixture of Ar, O2, N2 and H2 (for example 18 seem Ar, 0.75 seem O2, 13.25 seem N2);

- following the sputter deposition, the sample may be annealed at temperatures between of 50 and 1000 °C, preferably 475 °C, to enhance the luminescence;

- during annealing the annealing system may be flushed with gas containing H2 (93% N ₂ 17% H ₂ );

Hence, amorphous luminescent Sm ²⁺ doped inorganic thin-film layers may be formed on a substrate using a sputtering method. The method may comprise providing a sputtering target comprising Al, Si, Sm into the sputtering chamber; introducing a gas mixture that may include N2, H2, O2 into the sputtering chamber; and, applying an RF (or pulsed-DC) electric potential to said sputtering target, thereby causing sputtering of material from the target onto a substrate so that an amorphous thin-film of the Sm ²⁺ doped luminescent inorganic ionic compound is formed.

In an embodiment, a refractive index of the SiAION:Sm ²⁺ material may be selected between 1.5 and 2.1. The refractive index may be selected by selecting a predetermined O/N ratio during the sputtering process. This way, the refractive index of the SiAION :Sm ²⁺ material may be matched to the refractive index of the substrate (such as glass) on which the material was grown.

Additionally, in a further embodiment, the luminescent Tm ²⁺ doped SiAION material may be formed using a sputtering technique as described above. The synthesis of the SiAIO(N):Tm ²⁺ powder is identical to the synthesis of the SiAION:Sm ²⁺ powder with the exception that instead of Sm2O3 an amount of 0.0372 g Tm2O3 is used. The SiAION:Sm ²⁺ material absorbs radiation in the UV band, the visible band and part of the near-infrared band of the solar spectrum and converts radiation in these bands into radiation of a predetermined nearinfrared band of the spectrum. In particular, the luminescent Tm ²⁺ doped SiAION material exhibits infrared emission in the 1100-1200 nm band, including a sharp emission peak around 1140 nm. The Tm ²⁺ doped SiAION material exhibits broadband absorption of radiation in the solar spectrum, no self-absorption and has excellent optical and mechanical properties.

A synthesis method for producing a SiAION :Sm ²⁺ nanoparticle material may include the steps of:

- stoichiometrically weighting 3.8736 g Si(OC2H5)4, 0.1650 g AI(NO3)3, 0.0338 g Sm2O3, 0.1630 g C6H8O7*H2O (AI:CA = 1 :1 mol);

- dissolving the Sm2O3 in diluted nitric acid;

- dissolving surfactant CA (citric acid) in the previous solution;

- dissolving AI(NO3)3 in the previous solution;

- dissolving TEOS (Si(OC2H5)4) dropwise in the previous solution;

- evaporating the mixture on the heating plate to form ~ 30 ml of sol;

- ageing the sol for 24 hours at 40oC in the dryer to form gel structure;

- calcinating at 700 °C for 5 hours in air to remove any residual organic content;

- sintering at 1000 °C for 1 hour under a reducing atmosphere;

- grinding the product in an agate mortar to form nanopowder having an (average) particle desired size for example 20 and 400 nm.

Based on these steps a SiAIO(N):Sm ²⁺ nanoparticle material is produced wherein per 1 molar SiAIO(N):Sm ²⁺ product; Sm is about 1mol% of cations (Si and Al) and the Si/AI ratio is 24.

Nanoparticles of the SiAION:Sm ²⁺ material will have an average particle size between 1 to 900 nm, preferably between 1 to 500 nm, more preferably between 1 and 50 nm. Microparticles of the SiAION:Sm ²⁺ material will have a size between 0.5 and 50 micron, 0.8 and 20 micron or 1 micron and 10 micron. Typically, the SiAION:Sm ²⁺ particles will be of an amorphous material. The crystallinity can be increased by elevating the sintering temperature, which stimulates localized SiO2 phase formation. The increased crystallinity may enhance luminescence but may also increase light scattering.

A synthesis method for producing a SiAION :Sm ²⁺ microparticle material may include the steps of:

- stoichiometrically weighting 0.6521 g a-Si3N4, 0.0395 g AI2O3, 0.2799 g SiO2, 0.0338 g Sm2O3;

- mixing and grinding all the powder mixture in an agate mortar or ball mill;

- sintering the mixture at 1500 C for 8 hours under reducing atmosphere;

- grinding the product in an agate mortar or ball mill to form a powder having an (average) particle size between 1 and 50 micron. Based on these steps a SIAIO(N):Sm ²⁺ micropartide material is produced wherein per 1 molar SiAIO(N):Sm ²⁺ product; Sm is about 1mol% of cations (Si and Al) and the Si/AI ratio is 24.

Fig. 3-5 depict schematic cross-sections of luminescent solar concentrator devices, comprising a waveguide structure comprising a luminescent coating and a silver containing reflecting coating according to various embodiments. For example, Fig. 3 depicts a solar radiation conversion device 300 including at least one waveguide structure. The waveguide structure may have the form of a slab or a glazing pane of a transparent organic or inorganic material 304, e.g. glass, comprising a first (top) surface, a second (bottom) surface and one or more edges.

At least part of the top and/or bottom surface of the waveguide structure may be covered with a luminescent layer 306, e.g. a thin-film luminescent layer, that may comprise an inorganic luminescent material as described in this specification. Further, a silver containing reflecting layer 308 as described with reference to the embodiments in this disclosure is provided on the surface opposite to the surface on which the luminescent layer is provided. At least part of the edges of the waveguide structure may be coupled to at least one photovoltaic device 312.

Radiation from the UV band and part of the visible band of the solar spectrum is converted by the luminescent conversion layer into radiation of a visible red/near infrared band (e.g. the 650-800 nm band associated with radiation transmitted by the Sm ²⁺ ions) and/or into radiation of the near-infrared band (e.g. the 1100-1250 nm band associated with radiation transmitted by Tm ²⁺ and/or Mn ⁵⁺ ions).

In an embodiment, the thin-film luminescent layer may be an inorganic luminescent (poly)crystalline or an amorphous thin-film layer that is formed on the waveguide structure. The thin-film layer may be formed over or onto the waveguide structure using a deposition technique e.g. a (co-)sputtering or a reactive co-sputtering method as described above. The use of an amorphous or (poly)crystalline thin-film layer that is coupled as an optically active layer to the waveguide structure provides the advantage that scattering which may occur when using a matrix layer comprising doped particles may be eliminated or at least substantially reduced. In another embodiment, the thin-film luminescent layer may be formed of a transparent matrix material in which particles (not shown), nanoparticles and/or microparticles, of an inorganic luminescent material as described in this specification are embedded.

Fig. 4 depicts an embodiment of a luminescent solar concentrator device, wherein the waveguide structure comprises a layer of a transparent organic or inorganic matrix material 404 in which particles 406, preferably nanoparticles or microparticles, of an inorganic luminescent material as described in this disclosure are embedded. When solar radiation 402 enters the top surface of the waveguide structure part of the radiation is absorbed by one or more energy bands of the dopant sites in the luminescent particles. Further, a silver containing reflecting layer 308 as described with reference to the embodiments in this disclosure is provided on the bottom surface (opposite to the light receiving top surface). At least part of the edges of the waveguide structure may be coupled to at least one photovoltaic device 312.

Excited dopant sites may convert the absorbed solar radiation into radiation 410 in a predetermined narrow emission band as described in the embodiments of this application, e.g. an emission band in the visible red band and/or the near infrared band of the spectrum. At least part of the radiation emitted by excited dopants may be guided via the waveguide structure towards the edges of the waveguide. A photovoltaic cell 512 connected to the edge of the waveguide structure may convert photons originating from the edge emitting waveguide structure into electrical power.

Doped particles, microparticles and/or nanoparticles, of an inorganic luminescent material as described in this disclosure may be embedded in a transparent organic or inorganic matrix material that has excellent transmittance properties in the nearinfrared range of the optical spectrum. In an embodiment, organic transparent matrix materials may include poly(methyl methacrylate) (PMMA) or a polycarbonate. In another embodiment, inorganic transparent matrix materials may include a glass material. In an embodiment, the refractive index of the matrix material may be selected to match the refractive index of doped microparticles so that losses due to scattering of the emitted light out of the waveguide structure is minimized.

Fig. 5 depicts an embodiment of a luminescent solar concentrator device comprising one or more luminescent layers that are similar to those described with reference to Fig. 3. In this embodiment however, one or more luminescent layers 506 are embedded in the waveguide structure. The structure may include a first glazing pane, a luminescent layer 306, e.g. a thin-film luminescent layer, provided over a first surface of the first glazing pane and a silver containing reflecting layer 308 provided over a second surface that is opposite to the first surface. A second glazing pane may be provided over, e.g. bonded to, the luminescent layer so that the luminescent layer is embedded in a glass waveguide structure. A photovoltaic cell 512 connected to the edge of the waveguide structure may convert the photons originating from the edge emitting waveguide structure into electrical power.

In an embodiment, the at least one photovoltaic device may be optimized for transforming radiation in the near-infrared band (as generated by the luminescent material) into electric power. For example, in an embodiment, the photovoltaic device may comprise a Copper Indium Gallium (di)Selenide (CIGS) material. In another embodiment, the photovoltaic device may comprise a Copper Indium (di)Selenide (CIS) material. These materials are very efficient for converting emitted near-infrared radiation emitted by the excited dopant sites into electrical energy. In a further embodiment, the photovoltaic device may comprise a NIR/IR absorbing organic layer or a NIR/IR dye-sensitized layer. In an embodiment, the photovoltaic cell may comprise an organic semiconducting layer, e.g. MEH- PVV, that is sensitized with NIR/IR absorbing quantum dots. For example, by controlling the size of low-band gap (binary) semiconductors (e.g. PbS, PbSe, InAs and/or HgTe) quantum dots, the quantum dots may be tailored to absorb in the (near) infrared spectrum between 900 and 2000 nm. See e.g. Sargent et al in Solution-based Infra-Red Photovoltaic Devices, Nature Photonics 3, 325 - 331 (2009). In another embodiment, the photovoltaic cell may comprise a (single) walled carbon nano-tube layer or a graphene active NIR/IR absorbing layer.

In another embodiment, the at least one photovoltaic device may be optimized for transforming radiation in the red visible I near infrared band (as generated by the luminescent material) into electrical power. For example, photovoltaic devices including one or more layers of an IV and lll-V semiconductor, including e.g. crystalline (e.g. poly, micro or nanocrystalline) or amorphous silicon solar modules, gallium arsenide (GaAs) type modules, cadmium telluride (CdTe) type modules and/or indium phosphide (InP) solar modules.

The devices depicted in Fig. 3-5 are non-limiting examples of luminescent solar concentrator devices and many variations and/or combinations of features of embodiments in this disclosure are possible without departing the invention. For example, in an embodiment, a solar radiation conversion device may comprise a waveguide structure comprising one or more inorganic luminescent layers provided over the first and/or second surface of the waveguide structure and one or more inorganic luminescent layers embedded in the waveguide structure. In a further embodiment, one or more Tm ²⁺ , Mn ⁵⁺ and/or Sm ²⁺ doped SiAION thin-films may be part of an anti refl ection layer, protective barrier layer and/or thermal barrier layer provided over the waveguide structure. In a further embodiment, at least part of the photovoltaic cell may be part of or integrated with the waveguide structure. In yet a further embodiment, one or more optical layers may be provided over the first and second surfaces of the waveguide structure wherein at least part of the optical layers have refractive and/or reflective properties selected to improve the waveguiding properties of the waveguide structures.

Fig. 6 depicts an example of a cross-sectional view of a glazing unit according various embodiments. The glazing unit may include a first (outer) glass pane 602i and a second (inner) glass pane 6022 wherein the peripheral areas (at the edges) of the glass panes are bonded to a spacer structure 604 so that the parallel surfaces of the glass panes are fixed at a predetermined distance. This way an inner-pane space may be formed between the first and second glass panes. A seal 606 structure be used to seal the space between the two glass panes.

The first (outer) glass pane may be coated according to the embodiments described in this disclosure. For example, the outer surface of the first glass pane may comprise a first luminescent coating comprising a first luminescent layer 602i and the inner surface opposite to the outer surface of the first glass pane may comprise a first silver- containing coating. In an embodiment, the first silver-containing coating may comprise one or more thin-film silver layers. This way, radiation 614 in one or more bands of the solar spectrum incident to the first glass pane will be partly transformed by the first liminescent layer into radiation of another wavelength. At least part of the radation 618 emitted by the luminescent layer 616 will transmitted via internal reflection towards the edges of the glass pane where it will be absorbted by the photovoltaic cell. The first silver containing coating will substantially enhance the amount of light that is internally reflected towards the edges, while still providing a glass pane that is substantially transparent for visible light. Preferably, the radiation emitted by the first luminescent layer is narrow band radation from the red or NIR part of the spectrum that matches the absorption band of a photovoltaic cell arranged at the edge of the first glass pane.

As described with reference to the embodiments in this disclosure, the silver- containing both provides an enhancement of the are configured to reflect radiation generated by the luminescent material. For example, the reflection layers may be optimized for reflecting radiation of a visible red/near infrared band (e.g. the 650-800 nm band associated with radiation transmitted by the Sm ²⁺ ions) and/or radiation of a near-infrared band (e.g. the 1150-1250 nm band associated with radiation transmitted by Tm ²⁺ and/or Mn ⁵⁺ ions).

Since SiAION layers are also used as dielectric barriers, luminescent layers may also be provided over (part of the) outer surfaces of the first and/or second glass panes. (For example, SiAION:Sm ²⁺ or SiAION:Tm ²⁺ layers may be provided as part of a dielectric barrier over at least part of the outer surfaces of the first and/or second glass panes. Additionally, a Mn ⁵⁺ doped layer may be provided over at least part of the outer surfaces of the first and/or second glass panes, wherein the Mn ⁵⁺ doped layer is protected by one or more non-doped SiAION layers and/or one or more SiAION:Sm ²⁺ or SiAION:Tm ²⁺ layers.

Hence, when the outer glass pane is exposed to sunlight, radiation of the solar spectrum 614 may hit the first luminsecent layer 610i. Part of the radiation of the solar spectrum may be absorbed and converted to specific bands in the visible red light and/or near-infrared. Thus, an excited dopant 616 of the first luminescent layer may transmit radiation 618 which captured by internal reflection in the outer glass pane, wherein the first silver-containing reflection layer 612i enhances the amount of light is reglected towards a first photovoltaic device 632i.

In further other embodiments, the second (inner) glazing pane may include a second luminescent layer 6102 and a second silver-containing refleecting layer 6122. This way, part of the radiation of the solar spectrum that has passed the first luminescent glazing pane may be absorbed and converted to specific bands in the visible red light and/or nearinfrared by the second luminescent layer. Thus, an excited dopant 620 of the second luminescent layer may transmit radiation 618 which captured by internal reflection in the inner glass pane, wherein the second silver-containing reflection layer 6122 enhances the amount of light that is reflected towards a second photovoltaic device 6322.

The luminescent glazing unit depicted in Fig. 6 is just a non-limiting example of luminescent glazing units. For example, in some embodients, the glazing unit may include more than two glazing units. In another embodiments, the first luminescent layer may have different optical properties, e.g. in terms of obsortpion and/or emission, than the second luminescent layer.

The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. As used herein, the singular forms "a," "an," and "the" are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms "comprises" and/or "comprising," when used in this specification, specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof.

The corresponding structures, materials, acts, and equivalents of all means or step plus function elements in the claims below are intended to include any structure, material, or act for performing the function in combination with other claimed elements as specifically claimed. The description of the present invention has been presented for purposes of illustration and description but is not intended to be exhaustive or limited to the invention in the form disclosed. Many modifications and variations will be apparent to those of ordinary skill in the art without departing from the scope of the appending claims and spirit of the invention. The embodiment was chosen and described in order to best explain the principles of the invention and the practical application, and to enable others of ordinary skill in the art to understand the invention for various embodiments with various modifications as are suited to the particular use contemplated.