Nanocomposites for luminescent solar concentrators (LSCS)

Abstract

It relates to a solar device comprising a luminescent solar concentrator (LSC), and at least one photoactive component capable of converting light into electrical energy, wherein the luminescent solar concentrator comprises a polymeric matrix capable of directing light to the photoactive component, or a film or sheet thereof, or a substrate (e.g. glass or another polymer material) where such film or sheet is adhered, wherein the polymeric matrix comprises: a) a water-soluble polymer, b) nanodroplets dispersed in the water-soluble polymer which comprise one or more oils and / or one or more phase change materials (PCMs), and c) optionally one or more luminescent dyes. It also relates construction elements comprising the LSCs, and to a method for generating electricity which comprises the step of exposing the solar device or the construction element to sunlight, whereby the polymeric matrix directs the sunlight to the photoactive component, and the photoactive component converts the concentrated light into electricity.

Description

[0001]Nanocomposites for Luminescent Solar Concentrators (LSCs)This application claims the priority of the European Patent Application 24382821.7 filed onJuly 25th, 2024. Technical FieldThe present invention relates to Luminescent Solar Concentrators (LSCs) based on apolymeric matrix capable of directing light to the photoactive component, wherein thematrix comprises a water-soluble polymer, nanodroplets dispersed therein and optionallyone or more luminescent dyes. It also relates to a solar device comprising the said LSC and at least one photoactive component capable of converting light into electrical energy,such as a photovoltaic or photoelectrolytic cell, on at least one of the edges of the LSC,and to a construction element comprising one or more of said solar devices.Background Art Energy demand and consumption is growing year after year and most of this energy produced comes from non-renewable fonts. For this reason, new strategies and methods are sought for obtaining energy in a more efficient way from green sources. In 1976 a planar solar collector with embedded luminescent species was proposed, capable of absorbing part of solar radiation and re-emitting photons toward its edges, where a photovoltaic (PV) cell was attached. This phenomenon is achieved because there-emitted photons, from dyes embedded in the host material, are internally reflectedwithin the collector due to the high difference of refractive index between the host material and air, which prevents the escape of the photons. As a result, the absorbed solar light is reemitted and sent and concentrated in the film edges, where it can be converted inelectric power by coupled PV cells.These devices designed to concentrate solar radiation into photovoltaic PV cells are known as luminescent solar concentrators (LSCs). Polymers (which commonly have refractive index between n = 1.4 and 1.5) or glass (n = 1.5) are normally used as hosts materials. Both types of materials offer high transparency and are easy to manufacture. LSCs are thus suggested as a low-cost alternative when semiconductor materials weretoo costly and represent a promising solution for building integrated photovoltaic cells(BIPVs), through transparent windows. Compared to standard photovoltaic cells, LSCs allow using building windows to capture the solar light and convert it into available current, without affecting the transparency of the windows and requiring a much less circuitry (i.e. lower costs), as the photovoltaic cells would only be installed on the edges of the window material. Moreover, such an approach avoids the need of areas specifically dedicated to large extensions of PV, avoiding also regulatory, space, orientation, and aesthetic issues. Since then, a lot of researchers have aimed to develop new generations of LSCs of higher efficiencies, reducing losses, making better choice of materials and luminescent species, and finding more applications. For example, Dias et al. (Applied Sciences 2022) discloses studies LSCs based on the incorporation of bio-based luminescent molecules into solid poly(vinyl alcohol) (PVA) matrices that can be easily processed as thin films. Further, Congiu et al (Solar Energy 2021) disclose aqueous photoactive microemulsions consisting of Sodium Dodecyl Sulphate (SDS) / 1-butanol / water / DTB (4,7-Dithien-2-yl-2,1,3- benzothiadiazole) in toluene as liquid LSCs. Despite the above, current LSCs are only partially used in smart windows technologies, as they suffer several issues, such as reduced fluorescence quantum yield of the dyes in the matrix, reabsorption problems due to their low Stokes shift, fatigue resistance and photodegradation, large amount of light escaping from the matrix, permanent emission,i.e., the dyes always emit the same type of emission, permanent coloration, i.e. the dyesabsorb always the same amount of light filtering it, regardless the weather conditions, andproduce aesthetic issues. Most of these issues are related to the intrinsic structure of the material, which consists in dyes directly embedded in the matrices. Therefore, from what is known in the state of the art, there is still the need of providing efficient, cost-effective, durable, and scalable LSC materials for the generation of electricity. Summary of Invention The inventors have developed new transparent materials based on oil and / or phasechange materials (PCM) nanodroplets embedded in a polymeric matrix, which are capableto concentrate incident light in its edges and thus work as luminescent solar concentrators (LSCs). Thus, these materials when used for example in windows can scatter and / orabsorb solar light, waveguide the scattered and / or emitted light to the edges and convert itinto usable current without affecting the window transparency by means of a photoactivecomponent such as a photovoltaic cell (PV), and reduce costs with respect to standard PV cells. The inventors have surprisingly found that while nanosize of the droplets mostly prevents scattering of the incident light, the little remaining scattering can be exploited to concentrate light of different wavelengths on the edges, without using photodegradable emissive dyes, which allows enlarging the lifetime of the LSC. Moreover, the materials of the invention are highly transparent materials, which makethem ideal for their application in smart windows or glasses and have further advantagessuch as flexibility and adaptability. The polymeric matrix can be configured into free-standing films or sheets that can be adapted to curved / flat surfaces. If desired, thematerials can also be embedded within polymers or glasses as laminates for furtherprotection and provide desired mechanical properties. Also, the film can be adhered orcast onto a substrate such as an adhesive transparent material which can be thus stickedto existing windows (doted of PV cells in the edges) by the users. Alternatively, the filmcan be adhered or cast directly onto a glass substrate.Furthermore, the nanodroplets embedded in a polymeric matrix may contain emissivedyes. The fact that the dyes are dissolved in a liquid inert medium provides photostability,thereby enlarging the lifetime of the dye. Moreover, the oil medium ensures the dyesdecrease their tendency to aggregate, resulting in the highest possible luminescencequantum yields. Thus, dye aggregation and loss of emission efficiency, are prevented,unlike what happens in standard LSCs where dyes are directly embedded in polymericmatrices, in particular in the form of films or sheets.As illustrated in the examples, the nanodroplets may contain a single dye or multiple dyes, which may also interact with each other such as dye-pairs undergoing Förster Resonance Energy Transfer (FRET), or dye-pairs undergoing Upconversion through triplet-triplet energy transfer (TTA-UC), or dye pairs undergoing excimer or exciplex emissions. The nanodroplets guarantee the dyes diffusion within the nanocontainer, allowing for energy- transfer processes which could be used to enlarge the Stokes-shift of the emission and minimize self-absorption.Additionally, the oxygen barrier properties of the polymer and the nanodroplets, allow touse phosphorescent dyes, which also benefit of a large Stokes shift and eliminate the problem of the self-absorption. By using PCM loaded with dyes as nanodroplets the emission between two differentfluorescent states may be shifted by inducing a phase change of the PCM.Overall, the materials of the invention permit overcoming and solving problems that reduce the efficiency and performance of current LSCs, due to their intrinsic structure.Therefore, a first aspect of the invention relates to a solar device comprising a luminescent solar concentrator (LSC), and at least one photoactive component capable of converting light into electrical energy, particularly at least one photovoltaic orphotoelectrolytic cell, wherein the luminescent solar concentrator comprises a polymericmatrix, wherein the polymeric matrix is particularly capable of directing light to thephotoactive component and comprises:a) a water-soluble polymer, and b) nanodroplets dispersed in the water-soluble polymer which comprise: i) one or more oils, or alternativelyii) one or more phase change materials (PCMs), or alternatively iii) one or more oils and one or more phase change materials (PCMs).The invention also relates to a method for generating electricity by using a polymericmatrix, particularly capable of directing light to the photoactive component, whichcomprises: a) a water-soluble polymer, and b) nanodroplets dispersed in the water-soluble polymer which comprise: i) one or more oils, or alternativelyii) one or more phase change materials (PCMs), or alternatively iii) one or more oils and one or more phase change materials (PCMs).The polymeric matrix may optionally comprise one or more luminescent dyes, particularlyone or more luminescent dyes encapsulated in the nanodroplets.A second aspect of the invention relates to a solar device comprising a luminescent solarconcentrator (LSC), and at least one photoactive component capable of converting light into electrical energy, particularly at least one photovoltaic or photoelectrolytic cell,wherein the luminescent solar concentrator comprises:A) a film or sheet, orB) a substrate onto which the film or sheet is adhered or cast;wherein the film or sheet A), or the substrate comprising the film or sheet B), arecapable of directing light to the photoactive component, and wherein the film or sheet A) comprises the polymeric matrix as previously definedand optionally one or more transparent excipients.The invention also relates to a method for generating electricity by using a film or sheetcomprising the polymeric matrix as previously defined or a substrate onto which the film orsheet is adhered or cast.A third aspect of the invention relates to a construction element comprising one or moresolar devices as previously defined.A fourth aspect of the invention relates to a method for generating electricity whichcomprises the step of exposing a solar device or the construction element as previouslydefined to sunlight, whereby the polymeric matrix directs the sunlight to the photoactivecomponent, and the photoactive component converts the concentrated light intoelectricity. Brief Description of Drawings FIG.1 shows the a) flexibility, b) transparency of the film under sunlight exposure, and c)transmittance spectra of the dyeless film of Example 1 (T refers to transmittance andlambda to wavelength). FIG.2 shows a) light collected at the edges of the dye-less film of Example 1 (M812@PVA, solid lines) and the comparative film of Example 2 (PMMA, discontinued lines) when irradiated with 450 nm, 532 nm, 589 nm, 650 nm; b) the film of Example 1 (M812@PVA) irradiated with 532 nm monochromatic light showing the light concentrationin the edges (I refers to emission intensity in the edges with arbitrary units (arb. u.)).FIG.3 shows a) emission spectrum of excitation Xe lamp and b) edge emission of the dyeless film of Example 1 (continuous line), comparative PMMA film without droplets of Example 2 (dotted line) and comparative PVA film without droplets of Example 3 (striped line) irradiated with Xe lamp. FIG.4 shows single-dye containing films containing a) DPA (Example 4), b) BPEA (Example 5), and c) PDI (Example 6) under sunlight exposure, and d) PtOEP (Example 7)irradiated with 532 nm laser. Spectra of the light collected at the edges of the films of e)Examples 4-7, irradiated with the corresponding excitation wavelength: 356 nm for DPA,405 nm for BPEA and PDI and 532 nm for PtOEP films.FIG.5 shows light collected at the edges of multiple-dye containing films of a) Examples8-10, and b) film of Examples 8 exposed to sunlight.FIG.6 shows a) the film of Example 11 showing blue (UC) emission in the center, where the laser beam hits the film, and mixed red (phosphorescence) and blue (UC) emission in the edges; b) blue (UC) and red (phosphorescence) emission measured at the edges of the film. FIG.7 shows the blue (UC) emission of the multiple-dye containing film deposited on glass of Example 12 irradiated with monochromatic light (532 nm). FIG.8 shows light collected at the edges of multiple-dye PMMA films without nanodroplets of Example 13.FIG.9 shows the emission spectra of the a) low- and b) high-concentrated (in dye) PCMnanodroplets-loaded films recorded at different temperatures, of the Examples 14-15. FIG.10 represents an embodiment of the invention and shows a solar device (1)comprising a luminescent solar concentrator (LSC) of rectangular shape (2), and aphotoactive component (3) capable of converting light into electrical energy, wherein theluminescent solar concentrator comprises a polymeric matrix (4) capable of directing lightto the photoactive component (3), wherein the polymeric matrix comprises nanodroplets(5) capable of concentrating light to at least one of the edges (6) of the polymeric matrix.FIG.11 represents a lateral view of the solar device shown in FIG.10. FIG.12 shows a lateral view of an embodiment of the invention and shows a solar device (1) comprising a luminescent solar concentrator (LSC) of rectangular shape (2), and a photoactive component (3) capable of converting light into electrical energy, wherein the luminescent solar concentrator comprises a substrate (7) onto which a sheet (8) is adhered or cast, wherein the sheet (8) comprises a polymeric matrix (4) capable of absorbing or scattering the incident light and the reemitted and scattered light is directed to the photoactive component (3), wherein the polymeric matrix comprises nanodroplets (5). FIG.13 A) shows a lateral view of an embodiment of the invention and shows a solar device (1) comprising a luminescent solar concentrator (LSC) of rectangular shape (2), and a photoactive component (3) capable of converting light into electrical energy, wherein the luminescent solar concentrator comprises a sheet (8) which comprises a polymeric matrix (4) capable of directing light to the photoactive component (3), wherein the polymeric matrix comprises nanodroplets (5), and (B) a view from above of the same embodiment. Detailed description of the invention All terms as used herein in this application, unless otherwise stated, shall be understood in their ordinary meaning as known in the state of the art. Other more specific terms as used in the present application are as set forth below and are intended to apply uniformly throughout the specification and claims unless an otherwise expressly set out definition provides a broader definition. The term "about" or “around” as used herein refers to a range of values ± 10% of a specified value. For example, the expression "about 10" or “around 10” includes ± 10% of 10, i.e., from 9 to 11. For the purposes of the present invention, all given ranges include both the lower and the upper endpoints of the range. Ranges given, such as temperatures, times, weights, and the like, should be considered approximate, unless specifically stated. The indefinite articles “a” and “an” as used herein are synonymous with “at least one” or “one or more.” Thus, as used herein, the singular forms ”a”, “an”, and also the definite article “the” include plural referents unless the context clearly dictates otherwise. The term “percentage (%) by weight” refers to the percentage of each ingredient of the composition in relation to the total weight of the composition. The term "nanodroplets" as used herein refers to liquid droplets having diameters in thenanometer range (1-1000 nm). The nanodroplets are homogeneously and directlydispersed within the polymer matrix, i.e., in direct contact with the polymer matrix. The term “capsule” refers to those capsules having dimensions from 5 nm to 10000 nm, and encompasses “microcapsules” and “nanocapsules”. Particularly, the term “microcapsules” refers to those capsules having microscale dimensions (equal to or higher than 1000 nm to 10000 nm). And the term “nanocapsules” refers to those capsules having nanoscale dimensions (from 5 nm to lower than 1000). The term “core-shell capsules” refers to capsules formed by a core and a shell surrounding the core of thenanodroplets as defined herein. The particle size of the capsules can be measured by anymethod known in the state of the art such as SEM, TEM, and DLS depending on the particle size. The term "alkane" refers to a branched or linear saturated hydrocarbon which contains the number of carbon atoms specified in the description or claims. Examples includeeicosane, tetracosane and octacosane. The term "alkene" refers to a branched or linearunsaturated hydrocarbon which contains the number of carbon atoms specified in thedescription or claims and that also contains at least one carbon-carbon double bond. Theterm "alkyne" refers to a branched or linear saturated hydrocarbon which contains thenumber of carbon atoms specified in the description or claims and that also contains atleast one carbon-carbon triple bond. The term “alkyl” refers to a straight or branched saturated hydrocarbon chain which contains the number of carbon atoms specified in the description or claims. Examples include, among others, the group methyl, ethyl, propyl, isopropyl, butyl, isobutyl, sec-butyl, and tert-butyl. The term “alkenyl” refers to a straight or branched unsaturated hydrocarbon chain which contains the number of carbon atoms specified in the description or claims, and that also contains at least one carbon-carbon double bond. Examples include, among others, the ethenyl, 2-propenyl, and 1-propenyl. The term “alkynyl” refers to a straight or branched unsaturated hydrocarbon chain which contains the number of carbon atoms specified in the description or claims, and that also contains at least one carbon-carbontriple bond. Examples include, among others, the ethynyl, 2-propynyl, and 1-propynyl.The term “polycyclic aromatic hydrocarbon” (PAH) as used herein refers to organic compounds that contain carbon and hydrogen and consist of two or more fused aromatic rings. Non-limiting examples of polycyclic aromatic hydrocarbons include acenes orpolyacenes, pyrene, rubrene, perylene, violanthrone, and the like.The expression “room temperature” means a temperature from 20 to 25 ºC. The expression “obtainable by” is used herein for defining a product (e.g., the polymericmatrix or a film or sheet thereof) by its preparation process and refers to the product thatcan be obtained through the preparation process disclosed herein. For the purposes ofthe invention, the expressions “obtainable”, “obtained” and similar equivalent expressionsare used interchangeably and, in any case, the expression “obtainable” encompasses theexpression “obtained”.For the purposes of the invention, the term “transparent” refers to a material having theproperty of transmitting light (in the range between 400 and 750 nm) without appreciable scattering so that bodies lying beyond are clearly seen. It means that the material has a light transmittance equal to or higher than 70%, more particularly equal to or higher than 71%, 72%, 73%, 74%, 75%, 76%, 77%, 78%, 79%, 80%, 81%, 82%, 83%, 84%, 85%, 86%, 87%, 88%, 89%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or equal to 100%; being the transmittance measured by means of a UV-Visible spectrophotometer, particularly at 550 nm and at room temperature, or alternatively a haze equal or lower than 3%, more particularly equal to or lower than 2.9%, 2.8%, 2.7%, 2.6%, 2.5%, 2.4%, 2.3%, 2.2%, 2.1%, 2%, 1.9%, 1.8%, 1.7%, 1.6%, 1.5%, 1.4%, 1.3%, 1.2%, 1.1%, 1%,0.9%, 0.8%, 0.7%, 0.6%, 0.5%, 0.4%, 0.3%, 0.2%, and 0.1%; being the haze measuredby haze-meter. The term “solar device” as used herein refers to a single device, a plurality of devices able to provide heating, cooling, and / or electrical or mechanical power, by collecting and transferring solar generated energy into such uses either by active or passive means. Such systems may also store energy to be used at a later stage. The solar devicecomprises the combination of a LSC and a photoactive component such as a photovoltaicor photoelectrolytic cell, wherein these are configured to concentrate solar light in the LSC and transport the concentrated light and / or luminescence generated in the LSC to the photoactive component. The term "edge", as used herein, refers to the outermost boarder line of a material, e.g.the polymeric matrix, the film, the sheet, the substrate or the LSC.For the purposes of the invention, the expressions “waveguided to the edges”, “sent to the edges” or “directed to the edges” are used interchangeably. As mentioned above, a first aspect of the invention relates to a solar device comprising a luminescent solar concentrator (LSC), and at least one photoactive component capable of converting light into electrical energy, wherein the luminescent solar concentrator comprises a polymeric matrix capable of directing light to the photoactive component, wherein the polymeric matrix comprises:a) a water-soluble polymer, andb) nanodroplets dispersed in the water-soluble polymer which comprise: i) one or more oils, or alternativelyii) one or more PCMs, or alternatively iii) one or more oils and one or more phase change materials (PCMs).In another embodiment, optionally in combination with one or more features of the variousembodiments described above or below throughout all the description, the nanodroplets are capable of concentrating light to at least one of the edges of the polymeric matrix.For the purposes of the invention, the term “water-soluble polymer” refers to a variety ofsynthetic, semisynthetic, and natural materials. Although they differ in molecular structure, these polymers have in common that all are soluble in water, i.e., they are completely dissolved in water after a period of time (e.g.30 minutes) under stirring, particularly at atemperature in the range from 20 to 100 °C, at reflux.The polymeric matrix may comprise a single water-soluble polymer or a mixture of one ormore polymers. The water-soluble polymers are used as host materials and are capableof acting as emulsion stabilizers and as film or sheet-forming polymers. The water-solublepolymers should have a relatively high refractive index compared the refractive index ofthe air (n = 1.0003) in order to prevent the escape of the photons from the polymericmatrix. Additionally, the water-soluble polymers should be capable of being cast into a filmor sheet or solid mass.Non-limiting examples of water-soluble polymers that may be used in the presentinvention include polyalkylene alcohols such as polyvinyl alcohol (PVA), polyalkylenepyrrolidones such as polyvinylpyrrolidone (PVP), polyacrylamide, (C1-C6)alkyl celluloses such as methylcellulose, ethylcellulose or ethyl methylcellulose, hydroxy(C1-C6)alkyl celluloses such as hydroxyethylcellulose or hydroxyethyl methylcellulose, polyacrylates, polymethacrylates, polymethylmethacrylates, polyurethanes, polycarbonates,polysulphone, polyimides, polyetherimides, chitosan, gelatin, arabic gum and derivatives,or mixtures thereof.In one embodiment, optionally in combination with one or more features of the various embodiments described above or below throughout all the description, the polymericmatrix comprises a water-soluble polymer in an amount from 50 to 95%, more particularlyfrom 70 to 90%, by weight with respect to the total matrix weight. In one embodiment,optionally in combination with one or more features of the various embodiments describedabove or below throughout all the description, the polymeric matrix comprises a water-soluble polymer in an amount about 50%, about 51%, about 52%, about 53%, about 54%,about 55%, about 56%, about 57%, about 58%, about 59% about 60%, about 61%, about62%, about 63%, about 64%, about 65%, about 66%, about 67%, about 68%, about 69%,about 70%, about 71%, about 72%, about 73%, about 74%, about 75%, about 76%, about77%, about 78%, about 79%, about 80%, about 81%, about 82%, about 83%, about 84%,about 85%, about 86%, about 87%, about 88%, about 89%, about 90%, about 91%, about92%, about 93%, about 94%, or about 95% by weight with respect to the total matrixweight.In another embodiment, optionally in combination with one or more features of the variousembodiments described above or below throughout all the description, the polymericmatrix comprises a water-soluble polymer which is transparent, more particularly, has alight transmittance equal to or higher than 70%. In another embodiment, optionally in combination with one or more features of the various embodiments described above or below throughout all the description, the polymericmatrix comprises a water-soluble polymer which has a refractive index which is higherthan the refractive index of the air at standard temperature and pressure conditions (n =1.0003). If more than one water-soluble polymers are contained in the matrix, then this embodiment has to be understood such that the refractive index of the mixture of water- soluble polymers is higher than the refractive index of the air at standard temperature andpressure conditions (n = 1.0003).In another embodiment, optionally in combination with one or more features of the various embodiments described above or below throughout all the description, the polymericmatrix comprises a water-soluble polymer which has a refractive index equal to or higherthan 1.1, more particularly, equal to or higher than 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, or 1.8. Ifmore than one water-soluble polymers are contained in the matrix, then this embodiment has to be understood such that the refractive index of the mixture of water-soluble polymers equal to or higher than 1.1, more particularly, equal to or higher than 1.2, 1.3,1.4, 1.5, 1.6, 1.7, or 1.8. In another embodiment, optionally in combination with one ormore features of the various embodiments described above or below throughout all thedescription, the polymeric matrix comprises a water-soluble polymer which has arefractive index of about 1.1, about 1.15, about 1.2, about 1.25, about 1.3, about 1.35, about 1.4, about 1.45, about 1.5, about 1.55, about 1.6, about 1.65, about 1.7, about 1.75, about 1.8. In another embodiment, optionally in combination with one or more features of the various embodiments described above or below throughout all the description, the polymericmatrix comprises one water-soluble polymer, more particularly selected from the groupconsisting of PVA, polyvinylpyrrolidone (PVP), polyacrylamide, ethylcellulose, hydroxyethyl cellulose and mixture thereof. Even more particularly, the polymeric matrix comprises one water-soluble polymer which is PVA. The term “polyvinyl alcohol (PVA)” as used herein refers to a polymer having an average molecular weight (Mw) from 1,000 to 1,000,000 g / mol, particularly from 5,000 to 250,000, more particularly from 15,000 to 150,000, and having a hydrolysis degree from 60-99%, being hydrolysis degree defined as the percent completion of the reaction where acetate groups on the resin are substituted with hydroxyl groups. The polymeric matrix of the invention comprises nanodroplets dispersed in the water-soluble polymer. In one embodiment, optionally in combination with one or more featuresof the various embodiments described above or below throughout all the description, the nanodroplets are homogeneously dispersed in the water-soluble polymer.In another embodiment, optionally in combination with one or more features of the variousembodiments described above or below throughout all the description, the polymericmatrix comprises the nanodroplets of one or more oils and / or one or more PCMs in anamount from 5 to 50%, more particularly from 15 to 40%, by weight with respect to thetotal matrix weight. In one embodiment, optionally in combination with one or morefeatures of the various embodiments described above or below throughout all the description, the polymeric matrix comprises the nanodroplets in an amount about 5%,about 6%, about 7%, about 8%, about 9%, about 10%, about 11%, about 12%, about13%, about 14%, about 15%, about 16%, about 17%, about 18%, about 19%, about 20%,about 21%, about 22%, about 23%, about 24%, about 25%, about 26%, about 27%, about28%, about 29%, about 30%, about 31%, about 32%, about 33%, about 34%, about 35%,about 36%, about 37%, about 38%, about 39%, about 40%, about 41%, about 42%, about43%, about 44%, about 45%, about 46%, about 47%, about 48%, about 49%, or about50%, by weight with respect to the total matrix weight. In another embodiment, optionally in combination with one or more features of the various embodiments described above or below throughout all the description, the nanodropletshave a diameter from 10 to 400 nm, more particularly from 20 to 200 nm. Even moreparticularly, the nanodroplets have a diameter equal to or higher than 30 nm and equal toor lower than 150 nm. The size of the PCM nanodroplets can be determined byTransmission electron microscopy (TEM), e.g., using a Jeol 1400 microscope, with anacceleration voltage between 40 and 120 kV and dynamic light scattering, using MalvernZ-sizer. The size of the oil nanodroplets can be determined by dynamic light scattering,using Malvern Z-sizer. The nanodroplets comprised in the polymeric matrix made of the water-soluble polymercomprises one or more oils or one or more phase change materials (PCMs).For the purposes of the invention, the term "oil" means a neutral chemical substance of animal, vegetable, or mineral origin which is a liquid at ambient temperatures and is immiscible with water. Non-limiting examples of oils include alkanes and other mineral oils, silicone oils, vegetable oils such as acid triglycerides such as for example caprylic / capric triglyceride oil (Miglyol® 812), caprylic / capric / succinic triglyceride oil(Miglyol® 829), propylene glycol dicaprylate / dicaprate oil (Miglyol® 840), coconut oil,dioctyl terphthalate, diethyl phthalate, dioctly phthalate, diisononyl phthalate, diisodecyladipate, polyethylenglycol 2-ethylhexanoate, diethylhexyl sebacate, dioctyl sebacate,polyphenylmethyl-siloxane oils (~ 20 mPa s and ~ 1000 mPa s, respectively),hexadecane, hexylbenzene, 3-phenyl-1,10-bicyclohexyl, and mixtures thereof.The term “phase change material” or PCM refers to a substance presenting high latent heats of fusion, storing and releasing large amounts of energy upon melting and solidification, respectively. For the purpose of the invention, the term “PCM” refers to a material that is capable of changing from solid state to liquid state upon the absorption of heat and capable of changing from liquid state to solid state by the release of heat. The ability to store or release latent heat means the PCM may be used to regulate temperature in an environment and / or provide a cooling and / or heating effect. Non-limiting examples of PCMs include (C8-C52)alkane such as hexadecane, eicosane, tetracosane, octacosane, docosane, octadecane; (C14-C50)alkene, (C14-C50)alkyne, (C1-C30)alkyl-COOH such as decanoic acid, dodecanoic acid (lauric acid), tetradecanoic acid (myristic acid), hexadecanoic acid (palmitic acid), octadecanoic acid (stearic acid); (C1-C30)alkyl-COO-(C1-C30)alkyl such as methyl decanoate (methyl laurate), methyl tetradecanoate (methyl myristate), methyl octadecanoate (methyl stearate); (C1-C30)alkyl- OH such as tetradecanol or hexadecanol, (C1-C30)alkyl-O-(C1-C30)alkyl, (C1-C20)alkyl-NH2, (C1-C20)alkyl-NH-(C1-C20)alkyl, (C1-C20)alkyl-N-((C1-C20)alkyl)2, (C1-C20)alkyl-NHCO- (C1-C20)alkyl, ((C1-C20)alkyl)2-NCO-(C1-C20)alkyl, (C1-C20)alkyl-N(CO-(C1-C20)alkyl)2, (C2-C30)alkenyl-COOH, (C2-C30)alkenyl-COO-(C2-C30)alkenyl, (C2-C30)alkenyl-OH, (C2-C30)alkenyl-O-(C2-C30)alkenyl, (C2-C20)alkenyl-NH2, (C2-C20)alkenyl-NH-(C2- C20)alkenyl, (C2-C20)alkenyl-N-((C2-C20)alkenyl)2, (C2-C20)alkenyl-NH-CO-(C2-C20)alkenyl, ((C2-C20)alkenyl)2-NCO-(C2-C20)alkenyl, (C2-C20)alkenyl-N(CO-(C2-C20)alkenyl)2, (C1-C30)alkyl-COO-(C2-C30)alkenyl, (C2-C30)alkenyl-COO-(C1-C30)alkyl, (C1-C30)alkyl-O- (C2-C30)alkenyl, (C1-C20)alkyl-NH-(C2-C20)alkenyl, (C1-C20)alkyl-N-((C2-C20)alkenyl)2, ((C1-C20)alkyl)2-N-(C2-C20)alkenyl, (C1-C20)alkyl-NH-CO-(C2-C20)alkenyl, (C2-C20)alkenyl- NH-CO-(C1-C20)alkyl, ((C1-C20)alkyl)2-NCO-(C2-C20)alkenyl, ((C2-C20)alkenyl)2-NCO- (C1-C20)alkyl, (C1-C20)alkyl-N(CO-(C2-C20)alkenyl)2, (C2-C20)alkenyl-N(CO-(C1-C20)alkyl)2, (C2-C30)alkynyl-COOH, (C2-C30)alkynyl-COO-(C2-C30)alkynyl, (C2-C30)alkynyl-OH, (C2-C30)alkynyl-O-(C2-C30)alkynyl, (C2-C20)alkynyl-NH2, (C2-C20)alkynyl-NH-(C2-C20)alkynyl, (C2-C20)alkynyl-N-((C2-C20)alkynyl)2, (C2-C20)alkynyl-NH-CO-(C2-C20)alkynyl, ((C2-C20)alkynyl)2-NCO-(C2-C20)alkynyl, (C1-C30)alkyl-COO-(C2-C30)alkynyl, (C2-C30)alkynyl-COO-(C1-C30)alkyl, (C1-C30)alkyl-O-(C2-C30)alkynyl, (C1-C20)alkyl-NH- (C2-C20)alkynyl, (C1-C20)alkyl-N-((C2-C20)alkynyl)2, ((C1-C20)alkyl)2-N-(C2-C20)alkynyl, (C1-C20)alkyl-NH-CO-(C2-C20)alkynyl, (C2-C20)alkynyl-NH-CO-(C1-C20)alkyl, ((C1-C20)alkyl)2-NCO-(C2-C20)alkynyl, ((C2-C20)alkynyl)2-NCO-(C1-C20)alkyl, (C1-C20)alkyl- N(CO-(C2-C20)alkynyl)2, (C2-C20)alkynyl-N(CO-(C1-C20)alkyl)2, glyceryl tridecanoate, glyceryl tritridecanoate, glyceryl tripalmitate, tripentadecanoin, glyceryl triheptadecanoate,glyceryl tristearate, glyceryl trinonadecanoate, or mixtures thereof.In one embodiment, optionally in combination with one or more features of the various embodiments described above or below throughout all the description, the polymeric matrix comprises nanodroplets comprising or consisting of one or more oils, particularlymineral oils or vegetal oils. More particularly, the one or more oils are selected from thegroup consisting of caprylic / capric triglyceride oil (Miglyol® 812), caprylic / capric / succinictriglyceride oil (Miglyol® 829), diisodecyl adipate, diethylhexyl sebacate, dioctyl sebacate,and a combination thereof. Even more particularly, the one or more oils are selected fromthe group consisting of caprylic / capric triglyceride oil (Miglyol® 812),caprylic / capric / succinic triglyceride oil (Miglyol® 829), diisodecyl adipate, diethylhexyl sebacate, dioctyl sebacate, and a combination thereof. In another embodiment, optionally in combination with one or more features of the various embodiments described above or below throughout all the description, the polymeric matrix comprises nanodroplets comprising or consisting of one or more PCMs. Moreparticularly, the one or more PCMs are selected from the group consisting of (C8-C52)alkanes, (C1-C30)alkyl-COOH, (C1-C30)alkyl-COO-(C1-C30)alkyl, (C1-C30)alkyl-OH, (C1- C30)alkyl-O-(C1-C30)alkyl, (C1-C20)alkyl-NH-(C1-C20)alkyl, (C1-C20)alkyl-N-((C1-C20)alkyl)2,and a combination thereof. Even more particularly, the one or more PCMs are selectedfrom the group consisting of hexadecane, eicosane, tetracosane, octacosane, docosane,octadecane, decanoic acid, dodecanoic acid (lauric acid), tetradecanoic acid (myristic acid), hexadecanoic acid (palmitic acid), octadecanoic acid (stearic acid), methyl decanoate (methyl laurate), methyl tetradecanoate (methyl myristate), methyloctadecanoate (methyl stearate), tetradecanol, hexadecanol, glyceryl tristearate, and acombination thereof. Even more particularly, the one or more PCMs are selected from thegroup consisting of eicosane, tetracosane, octacosane, glyceryl tristearate, methyl stearate, tetradecanol, hexadecanol, decanoic acid, dodecanoic acid, stearic acid, and a combination thereof. In another embodiment, optionally in combination with one or more features of the various embodiments described above or below throughout all the description, the polymeric matrix comprises nanodroplets comprising or consisting of a mixture of eicosane and octacosane, a mixture of eicosane and hexadecane, a mixture of eicosane and tetracosane, and a mixture of tetradecanol and glyceryl triestearate. In another embodiment, optionally in combination with one or more features of the various embodiments described above or below throughout all the description, the polymeric matrix comprises nanodroplets comprising or consisting of a mixture of eicosane and octacosane,particularly at a weight ratio from 9:1 to 1:9, more particularly from 6:4 to 4:6; a mixture ofeicosane and hexadecane at a weight ratio from 9:1 to 1:9, more particularly from 7:3 to3:7; a mixture of eicosane and tetracosane at weight ratio from 9:1 to 1:9, more particularly from 7:3 to 3:7; a mixture of tetradecanol and glyceryl triestearate at weight ratio from 9:1 to 1:9, more particularly from 7:3 to 3:7. In another embodiment, optionally in combination with one or more features of the various embodiments described above or below throughout all the description, the polymeric matrix comprises nanodroplets comprising or consisting of one or more oils as defined herein andone or more PCMs as defined herein. More particularly, in this embodiment the one or moreoils are selected from the group consisting of caprylic / capric triglyceride oil (Miglyol® 812),caprylic / capric / succinic triglyceride oil (Miglyol® 829), diisodecyl adipate, diethylhexyl sebacate, dioctyl sebacate, and a combination thereof; and the one or more PCMs are selected from the group consisting of eicosane and octacosane, a mixture of eicosane and hexadecane, a mixture of eicosane and tetracosane, and a mixture of tetradecanol and glyceryl triestearate. In another embodiment, optionally in combination with one or more features of the various embodiments described above or below throughout all the description, the nanodroplets contained in the polymeric matrix comprises the nanodroplets have a homogeneous composition. In another embodiment, optionally in combination with one or more features of the various embodiments described above or below throughout all the description, the nanodroplets contained in the polymeric matrix comprises the nanodroplets have a heterogeneouscomposition. The film or sheet can be made by nanodroplets of different oils, of differentPCMs or by nanodroplets of PCMs and oils. The nanodroplets contained in the polymeric matrix may optionally be encapsulated in the form of capsules such as core-shell capsules. In one embodiment, optionally in combination with one or more features of the various embodiments described above or below throughout all the description, the nanodroplets comprising one or more oils and / or one or more PCMs and optionally one or more luminescent dyes are in the form of capsules, more particularly in the form of core-shell capsules, even more particularly wherein the shell comprises one or more polymeric shell materials; particularly selected from the group consisting of organic polymeric shell materials and inorganic polymeric shell materials. Non-limiting examples of appropriate organic polymeric shell materials for the presentinvention include linear or crosslinked poly(methyl methacrylate), polystyrene, polyamide,polyurea, polyurethane, polycarbonate, polysulphone, polyether sulfone, polyetherimide and a mixture thereof. Examples of appropriate inorganic polymeric shell materials for the present invention include, but without limitation, SiO2, TiO2, VO2, and a mixture thereof. As mentioned above, in some embodiments of the present invention the polymeric matrixmay comprise one or more luminescent dyes. Thus, in a particular embodiment of theinvention, optionally in combination with one or more features of the various embodiments described above or below throughout all the description, the polymeric matrix comprises: a) a water-soluble polymer, b) nanodroplets dispersed in the water-soluble polymer which comprise: i) one or more oils, or alternatively ii) one or more phase change materials (PCMs), or alternatively iii) one or more oils and one or more phase change materials (PCMs), andc) one or more luminescent dyes. More particularly, the nanodroplets comprise either oneor more oils, or alternatively one or more PCMs, and have a diameter from 10 to 250 nm, more particularly from 30 to 150 nm. In one embodiment, optionally in combination with one or more features of the various embodiments described above or below throughout all the description, the one or moreluminescent dyes are encapsulated in the nanodroplets. Thus, in this embodiment thepolymeric matrix comprises: a) a water-soluble polymer, b) nanodroplets dispersed in the water-soluble polymer which comprise: i) one or more oils, or alternatively ii) one or more phase change materials (PCMs), or alternatively iii) one or more oils and one or more phase change materials (PCMs), andc) one or more luminescent dyes encapsulated in the nanodroplets.When PCMs are used for encapsulating dyes, the polymeric matrix may also comprise one or more additives that quench the emission of the dyes in one of the states of thePCM. Non-limiting examples of such quenchers include for example, amines such as N,N-dibutylaniline, N,N-dimethylaniline, N-methyloctadecylamine, octadecylamine and the like,that quench fluorescence by electron transfer. The polymeric matrix may also compriseone or more additives that activate the emission of the dyes via Förster ResonanceEnergy Transfer (FRET) in one of the states of the PCM, such as e.g. dyes of higherenergy such as e.g. BPEA for PDI or pyrene for perylene. The term "luminescent dye" as used herein refers to a molecule, particularly an organic molecule, which is capable of absorbing light from an outside energy source andreemitting it. Luminescent dyes absorb within the UV-visible-NIR range and emit in theUV-vis-NIR range. The term luminescent dye encompasses fluorescent and phosphorescent dyes. Non-limiting examples of luminescent dyes that can be used include rubrene, anthracene,9,10-diphenyl anthracene (DPA), 9,10-dimethylanthracene (DMA), 9,10-dicyanoanthracene (DCA), 9,10-bis (4-methylphenyl)-2-chloroanthracene, 9,10-bis(4-ethylphenyl)-2-chloroanthracene, 9,10-bis(4-propylphenyl)-2-chloroanthracene, 9,10- bis(4-tert-butyl-phenyl-2-chloroanthracene, 9,10-bis(4-methoxyphenyl)-2- chloroanthracene, 9,10-bis-(4-ethoxyphenyl)-2-chloroanthracene, 9,10- bis(phenylethynyl)anthracene (BPEA), 1-chloro-9,10-bis(phenylethynyl)anthracene, 1,8- dichloro-9,10-bis (phenylethynyl)anthracene, 1,5-dichloro-9,10- bis(phenylethynyl)anthracene, 2,5-di-chloro-9,10-bis(phenylethynyl)anthracene, 2-methyl- 9,10-bis(phenylethynyl)anthracene, 2-ethyl-9,10-bis(phenylethynyl)anthracene, 1,4- dimethyl-9,10-bis(phenylethynyl)anthracene, 1-methoxy-9,10- bis(phenylethynyl)anthracene, 5,12-Bis-(phenylethynyl) napthacene, 5,16,11,12- tetraphenylnapthacene, 5,12-bis(phenylethynyl)tetracene, 16,17-dihexyloxyviolanthrone, 16,17-didecycloxyviolanthrone, pyrene, Rhodamine B, Rhodamine 6G, Coumarin and derivatives, cyanine dyes and derivatives, perylene, 1,6,7,12-tetraphenoxy-N,N’-bis(2,6- diisopropylphenyl)-3,4,9,10-perylene dicarboximide (Lumogen® F Red 305-Basf), N,N’- bis-(sec-butyl)-1,6,7,12-tetra-(4-tert-butylphenoxy) perylene-3,4,9,10-tetracarboxylic diimide (PTDI), 1,6,7,12-tetraphenoxy-N,N’-bis(2,5-di-tert-butylphenyl)-3,4,9,10-perylene dicarboximide, 1,7-dichloro-6,12-diphenoxy-N,N’-bis(2,6-diisopropyl-phenyl)-3,4,9,10- perylene di-carboximide, 1,6,7,12-tetra(p-bromophenoxy)-N,N’-bis(2,6-diisopropylphenyl)- 3,4,9,10-perylene di-carboximide, 1,6,7,12-tetra(p-t-butylphenoxy)-N,N’’-dineopentyl- 3,4,9,10-perylenedicarboximide, 1,6,7,12-tetra(o-chlorophenoxy)-N,N’-bis(2,6- diisopropylphenyl)-3,4,9,10-perylene dicarboximide, 1,6,7,12-tetra(p-chloro-phenoxy)- N,N’-bis(2,6-diisopropylphenyl)-3,4,9,10-perylene dicarboximide, 1,6,7,12-tetra(p- fluorophenoxy)-N,N’-bis(2,6-diisopropylphenyl)-3,4,9,10-perylene dicarboximide, 1,6,7,12- tetraphenoxy-N,N’-diethyl-3,4,9,10-perylene dicarboximide, 1,7-dibromo-6,12-diphenoxy- N,N’-bis(2-isopropylphenyl)-3,4,9,10-perylene dicarboximide, N,N’’-didodecyl-1,6,7,12- tetrakis(4-t-butylpenoxy)-3,4,9,10-perylene tetracarboximide, N,N’-dihexadecyl-1,6,7,12- tetrakis(4-t-butylphenoxy)-3,4,9,10-perylenedicarboximide, N,N’-dioctadecyl-1,6,7,12- tetrakis(4-t-butylphenoxy)-3,4,9,10-perylenetetracarboximide, N,N'-bis(3-pentyl)perylene- 3,4,9,10-bis(dicarboximide) (PDI pentyl), N,N'-bis(3-hexylheptyl)perylene-3,4,9,10-bis(dicarboximide) (PDI 3-hexylheptyl), N,N’-bis(1-hexylheptyl)perylene-3,4,9,10-bis(dicarboximide) (PDI 1-hexylheptyl), 4,7-di(thien-2’yl)-2,1,3-benzothiadiazole (DTB),5,6-diphenoxy-4,7-bis(2-thienyl)-2,1,3-benzothiadiazole (DTBOP), 5,6-diphenoxy-4,7- bis[5-(2,6-dimethylphenyl)-2-thienyl]benzo[c]1,2,5-thiadiazole (MPDTBOP), 5,6- diphenoxy-4,7-bis[5-(2,5-dimethylphenyl)-2-thienyl]benzo[c]1,2,5-thiadiazole (PPDTBOP), 4,7-bis[5-(2,6-dimethylphenyl)-2-thienyl]benzo[c]1,2,5-thiadiazole (MPDTB), 4,7-bis[5- (2,6-di-iso-propylphenyl)-2-thienyl]benzo[c]1,2,5-thiadiazole (IPPDTB), 4,7-bis[4,5-(2,6- dimethylphenyl)-2-thienyl]benzo[c]1,2,5-thiadiazole (2MPDTB), 4,7-bis(7′,8′- dibutylbenzo[1′,2′-b′:4′,3′-b″]dithien-5′-yl)-benzo[c][1,2,5]thiadiazole (F500), 4,9-bis(7′,8′- dibutylbenzo[1′,2′-b′:4′,3′-b″]dith-ien-5′-yl)-naphto[2,3-c][1,2,5]thiadiazole (F521), 4,7-bis(5- (thiophen-2-yl)thiophen-2-yl)benzo[c][1,2,5]thiadiazole (QTB), 4,9-bis(thien-2′-yl)- naphto[2,3-c][1,2,5]thiadiazole (DTN), 4-4-diflouro-4-bora-3a,4a-diaza-s-indacenos (BODIPY) and derivatives, Platinum octaethylporphyrin (PtOEP), Palladium octaethylporphyrin (PdOEP), Zinc tetraphenylporphyrin (ZnTPP), meso-Tetraphenyl-tetrabenzoporphine palladium (Pd(TPBP)), Pt(II) meso-tetraphenyl tetrabenzoporphinePt(TPBP), Ruthenium bipyridyl complexes, ruthenium phenanthroline derivatives, Osmium tert-pyridine complexes and derivatives, or combinations thereof. In one embodiment, optionally in combination with one or more features of the various embodiments described above or below throughout all the description, the one or moreluminescent dyes are fluorescent dyes. In another more particular embodiment, the one ormore luminescent dyes are phosphorescent dyes. In another more particular embodiment,the one or more luminescent dyes are a combination of fluorescent and phosphorescentdyes. More particularly, the one or more luminescent dyes are fluorescent orphosphorescent dyes selected from the group consisting of optionally substituted polycyclic aromatic hydrocarbons and optionally substituted heteroatom-containing polycyclic aromatic hydrocarbons. Even more particularly, the one or more luminescent dyes are selected from the group consisting of fluorescent dyes such as DPA, BPEA, PDI,PTDI, 1,6,7,12-tetraphenoxy-N,N’-bis(2,6-diisopropylphenyl)-3,4,9,10-perylenedicarboximide (Lumogen® F Red 305-Basf), and phosphorescent dyes such as PtOEP,PdOEP, ZnTPP, Osmium tert-pyridine complexes and derivatives.In another embodiment, optionally in combination with one or more features of the variousembodiments described above or below throughout all the description, the one or moreluminescent dyes have a maximum of the absorption at a wavelength from 300 to 800 nm,more particularly from 350 to 700 nm. In another embodiment, optionally in combination with one or more features of the various embodiments described above or below throughout all the description, the one or moreluminescent dyes have a maximum of the emission at a wavelength from 400 to 1000 nm,more particularly from 420 to 900 nm. In another embodiment, optionally in combination with one or more features of the various embodiments described above or below throughout all the description, the one or moreluminescent dyes are those for which the difference between the wavelengthcorresponding to the maximum emission wavelength and the wavelength corresponding to the maximum absorption wavelength is from 5 to 250 nm, more particularly from 30 to 200 nm. In another embodiment, optionally in combination with one or more features of the various embodiments described above or below throughout all the description, the one or moreluminescent dyes are present in the polymeric matrix in an amount from 0.001 to 5%,more particularly from 0.001 to 1%, more particularly from 0.001 to 0.3%, by weight withrespect to the total matrix weight. In one embodiment, optionally in combination with oneor more features of the various embodiments described above or below throughout all thedescription, the polymeric matrix comprises the one or more luminescent dyes are presentin the polymeric matrix in an amount about 0.001%, about 0.005%, about 0.01%, about0.02%, about 0.03%, about 0.04, about 0.05%, 0.06%, about 0.07%, about 0.08, about0.09%, about 0.1%, about 0.15%, about 0.2%, about 0.25%, about 0.3%, about 0.35%,about 0.4%, about 0.45%, about 0.5%, about 0.55%, about 0.60%, about 0.65%, about0.70%, about 0.75%, about 0.80%, about 0.85%, about 0.90%, about 0.95%, about 1%,about 1.5%, about 2%, about 2.5%, about 3%, about 3.5%, about 4%, about 4.5% orabout 5% by weight with respect to the total matrix weight. In another embodiment, optionally in combination with one or more features of the various embodiments described above or below throughout all the description, the polymericmatrix comprises a single dye, particularly encapsulated in the nanodroplets.In another embodiment, optionally in combination with one or more features of the various embodiments described above or below throughout all the description, the polymericmatrix comprises more than one dye, particularly two, three or four dyes, more particularlywherein the dyes are encapsulated in the nanodroplets, even more particularly wherein each nanodroplet encapsulates all the different dyes. In another embodiment, optionally in combination with one or more features of the various embodiments described above or below throughout all the description, the polymeric matrix comprises more than one dye, particularly two, three or four dyes, more particularly wherein each dye is encapsulated in different nanodroplets. In another embodiment, optionally in combination with one or more features of the various embodiments described above or below throughout all the description, the polymeric matrix comprises two dyes encapsulated in the nanodroplets, even more particularly wherein each nanodroplet encapsulates all the different dyes, wherein the dyes are capable of undergo Förster Resonance Energy Transfer (FRET), i.e., wherein one dye acts as an energy donor and the other dye acts as energy acceptor, and the emission spectrum of the first dye overlaps, particularly in overlap equal to or higher than 10%, withthe absorption spectrum of the second dye and the dyes are close or less than the Försterradius (1-10 nm). More particularly, the energy donor is BPEA and the energy acceptor isPDI. In another embodiment, optionally in combination with one or more features of the various embodiments described above or below throughout all the description, the polymericmatrix comprises two types of dyes encapsulated in the nanodroplets, even moreparticularly wherein each nanodroplet encapsulates all the different dyes, wherein thedyes are capable of undergo Upconversion through triplet-triplet energy transfer (TTET),i.e., wherein one dye acts as triplet sensitizer and the other dye acts as triplet acceptorand annihilator (emitter). The distance between the molecules has to be less than 1 nm.More particularly, the triplet sensitizer is PtOEP and the triplet acceptor and annihilator is DPA. In another embodiment, optionally in combination with one or more features of the various embodiments described above or below throughout all the description, two or moresensitizers are encapsulated in the presence of an emitter in the same nanodroplet, sothat the light absorbed by the different dyes in different spectral regions can be transferred via TTET, to the same emitter, which then undergoes triplet-triplet annihilation and yield upconverted emission. In another embodiment, optionally in combination with one or more features of the various embodiments described above or below throughout all the description, the polymeric matrix comprises: a) a water-soluble polymer, and b) nanodroplets dispersed in the water-soluble polymer which comprise: i) one or more oils, or alternatively ii) one or more phase change materials (PCMs), or alternatively iii) one or more oils and one or more phase change materials (PCMs), andwherein the polymeric matrix is further characterized for the absence of any dyes. Moreparticularly, the nanodroplets comprise either one or more oils, or alternatively one ormore PCMs, and have a diameter from 50 to 400 nm, more particularly from 80 to 200nm. According to a particular embodiment, optionally in combination with one or more features of the various embodiments described above or below throughout all the description, in the first aspect of the invention the polymeric matrix comprises or consists of: a) a water-soluble polymer selected from the group consisting of polyvinyl alcohol (PVA), polyvinylpyrrolidone (PVP), polyacrylamide, ethylcellulose, hydroxyethyl cellulose and mixture thereof, more particularly PVA, and b) nanodroplets dispersed in the water-soluble polymer which comprise one or more oilsselected from the group consisting of caprylic / capric triglyceride oil (Miglyol® 812),caprylic / capric / succinic triglyceride oil (Miglyol® 829), diisodecyl adipate, diethylhexylsebacate, dioctyl sebacate, and a combination thereof; wherein the polymeric matrix isfurther characterized for the absence of any dyes. More particularly, the nanodroplets have a diameter from 50 to 400 nm, more particularly from 80 to 200 nm. More particularly, the water-soluble polymer or the mixture of the water-soluble polymers is present in an amount from 50 to 95%, more particularly from 70 to 90%, by weight; andthe nanodroplets are present in an amount from 5 to 50%, more particularly from 15 to40%, wherein the percentages are given with respect to the total matrix weight, and the sum of the weight percentages of all components of the polymeric matrix are 100%. According to another particular embodiment, optionally in combination with one or more features of the various embodiments described above or below throughout all the description, in the first aspect of the invention the polymeric matrix comprises or consists of: a) a water-soluble polymer selected from the group consisting of polyvinyl alcohol (PVA), polyvinylpyrrolidone (PVP), polyacrylamide, ethylcellulose, hydroxyethyl cellulose and mixture thereof, more particularly PVA, and b) nanodroplets dispersed in the water-soluble polymer which comprise one or morePCMs selected from the group consisting of eicosane, tetracosane, octacosane, glyceryltristearate, methyl stearate, tetradecanol, hexadecanol, decanoic acid, dodecanoic acid,stearic acid, and a combination thereof; wherein the polymeric matrix is furthercharacterized for the absence of any dyes. More particularly, the nanodroplets have a diameter from 50 to 400 nm, more particularly from 80 to 200 nm. More particularly, the water-soluble polymer or the mixture of the water-soluble polymers is present in an amount from 50 to 95%, more particularly from 70 to 90%, by weight; and the nanodroplets are present in an amount from 5 to 50%, more particularly from 15 to 40%, wherein the percentages are given with respect to the total matrix weight, and the sum of the weight percentages of all components of the polymeric matrix are 100%. According to another particular embodiment, optionally in combination with one or more features of the various embodiments described above or below throughout all the description, in the first aspect of the invention the polymeric matrix comprises or consists of: a) a water-soluble polymer selected from the group consisting of polyvinyl alcohol (PVA), polyvinylpyrrolidone (PVP), polyacrylamide, ethylcellulose, hydroxyethyl cellulose and mixture thereof, more particularly PVA, and b) nanodroplets dispersed in the water-soluble polymer which comprise one or more oilsselected from the group consisting of caprylic / capric triglyceride oil (Miglyol® 812),caprylic / capric / succinic triglyceride oil (Miglyol® 829), diisodecyl adipate, diethylhexyl sebacate, dioctyl sebacate, and a combination thereof; andc) one or more luminescent dyes, particularly encapsulated in the nanodroplets. Moreparticularly, the nanodroplets have a diameter from 50 to 400 nm, more particularly from 80 to 200 nm. More particularly, the water-soluble polymer or the mixture of the water- soluble polymers is present in an amount from 50 to 95%, more particularly from 70 to 90%, by weight; the nanodroplets are present in an amount from 5 to 50%, moreparticularly from 15 to 40%; and the one or more luminescent dyes are present in thepolymeric matrix in an amount from 0.001 to 5%, wherein the percentages are given with respect to the total matrix weight, and the sum of the weight percentages of all components of the polymeric matrix are 100%. According to another particular embodiment, optionally in combination with one or more features of the various embodiments described above or below throughout all the description, in the first aspect of the invention the polymeric matrix comprises or consists of: a) a water-soluble polymer selected from the group consisting of polyvinyl alcohol (PVA), polyvinylpyrrolidone (PVP), polyacrylamide, ethylcellulose, hydroxyethyl cellulose and mixture thereof, more particularly PVA, and b) nanodroplets dispersed in the water-soluble polymer which comprise one or morePCMs selected from the group consisting of eicosane, tetracosane, octacosane, glyceryltristearate, methyl stearate, tetradecanol, hexadecanol, decanoic acid, dodecanoic acid, stearic acid, and a combination thereof; andc) one or more luminescent dyes, particularly encapsulated in the nanodroplets. Moreparticularly, the nanodroplets have a diameter from 50 to 400 nm, more particularly from 80 to 200 nm. More particularly, the water-soluble polymer or the mixture of the water- soluble polymers is present in an amount from 50 to 95%, more particularly from 70 to 90%, by weight; and the nanodroplets are present in an amount from 5 to 50%, moreparticularly from 15 to 40%; and the one or more luminescent dyes are present in thepolymeric matrix in an amount from 0.001 to 5%, wherein the percentages are given with respect to the total matrix weight, and the sum of the weight percentages of all components of the polymeric matrix are 100%. According to another particular embodiment, optionally in combination with one or more features of the various embodiments described above or below throughout all the description, in the first aspect of the invention the polymeric matrix comprises or consists of: a) a water-soluble polymer selected from the group consisting of polyvinyl alcohol (PVA), polyvinylpyrrolidone (PVP), polyacrylamide, ethylcellulose, hydroxyethyl cellulose and mixture thereof, more particularly PVA, and b) nanodroplets dispersed in the water-soluble polymer which comprise one or more PCMs selected from the group consisting of eicosane, tetracosane, octacosane, glyceryl tristearate, methyl stearate, tetradecanol, hexadecanol, decanoic acid, dodecanoic acid, stearic acid, and a combination thereof; andc) one or more luminescent dyes, particularly encapsulated in the nanodroplets;d) one or more additives that quench or activate the emission of the dyes in one of thestates of the PCM. More particularly, the water-soluble polymer or the mixture of the water-soluble polymers is present in an amount from 50 to 95%, more particularly from 70 to 90%, by weight; and the nanodroplets are present in an amount from 5 to 50%, moreparticularly from 15 to 40%; and the one or more luminescent dyes are present in thepolymeric matrix in an amount from 0.001 to 5%, wherein the percentages are given with respect to the total matrix weight, and the sum of the weight percentages of all components of the polymeric matrix are 100%.The use of nanodroplets comprising PCMs and one or more luminescent dyes allowsdynamicity and fluorescence modulation. By changing the phase of the PCM, usingtemperature, light (if photothermic nanoparticles are present) or voltage (if a conductivelayer is present), emission can be modulated. This can be exploited to activate two different photoactive components such as photovoltaic cells put on the edges, depending on the state of the PCM. Thus, depending on the activated emission, two different processes can be activated (e.g. cooling and heating systems). It also forms part of the invention a polymeric matrix comprising: a) a water-soluble polymer, and b) nanodroplets dispersed in the water-soluble polymer which comprise one or more oils, in particular other than PCMs, wherein the polymeric matrix is further characterized for the absence of any dyes. The preparation of the polymeric matrix of the first aspect can be carried out by methodsknown in the art such as emulsification / cooling, spontaneous emulsification / solventdisplacement, emulsion-solvent evaporation, or alternatively hot-extrusion. It also forms part of the invention a process for the preparation of a polymeric matrix comprising: i) mixing one or more oils and / or one or more PCMs with optionally one or moreluminescent dyes and then mixing the resulting mixture with an aqueous solution of one ormore water-soluble polymers,ii) emulsifying the mixture of step (i) to obtain an emulsion, andiii) removing water to obtain the polymeric matrix. When the nanodroplets contain more than one oil or more than one PCM, the process may comprise an additional previous step of mixing the two or more oils or the two or more PCMs. Alternatively, the oils / PCMs in the form of nanodroplets in the emulsions maybe combined so that the oils / PCM are not mixed in the final film or sheet. When thenanodroplets contain one or more PCMs, the process may comprise an additionalprevious step of heating the one or more PCMs above their melting temperature such thatthey are in liquid state. The emulsification step is carried out through any method known in the art, for instance high-energy or low-energy methods. In the high energy method, the homogenization iscarried out by stirring, high-shear homogenization, ultrasonication, membrane filtration orhigh-pressure homogenization. The low-energy method includes the spontaneousemulsification and phase inversion methods. The nanodroplet size may be adjusted depending on the emulsification method. In one embodiment, optionally in combination with one or more features of the various embodiments described above or below throughout all the description, the polymericmatrix as defined in the first aspect of the invention optionally comprising one or moreluminescent dyes is obtainable by a process comprising:i) mixing one or more oils and / or one or more PCMs with optionally one or moreluminescent dyes and then mixing the resulting mixture with an aqueous solution of one ormore water-soluble polymers,ii) emulsifying the mixture of step (i) to obtain an emulsion, andiii) removing water to obtain the polymeric matrix. In one embodiment, optionally in combination with one or more features of the various embodiments described above or below throughout all the description, the emulsification step (ii) comprises stirring the mixture of step (i) until a homogeneous emulsion is obtained.Films and sheetsAs mentioned above, the second aspect of the invention relates to a solar devicecomprising a luminescent solar concentrator (LSC), and at least one photoactive component capable of converting light into electrical energy, wherein the luminescentsolar concentrator comprises: A) a film or sheet, or B) a substrate onto which the film orsheet is adhered or cast; wherein the film or sheet A), or the substrate comprising the film or sheet B), are capable of directing light to the photoactive component, and wherein the film or sheet A) comprises the polymeric matrix as previously defined. The films or sheets of the present invention are especially advantageous because apart from having the ability to concentrate light on their edges, they also allow creating a desired shape and / or curvature. For the purposes of the present invention, the term "free-standing film or sheet" refers to afilm or sheet which has a physically stable shape and is dimensionally stable on its castingsurface and can be removed from the casting surface without having to be supported over most of its surface area. All embodiments as defined herein for the polymeric matrix of the first aspect of the invention in relation to their components also apply to the films or sheets of the secondaspect of the invention.In one embodiment, optionally in combination with one or more features of the variousembodiments described above or below throughout all the description, the film or sheet isa free-standing film or sheet. In another embodiment, optionally in combination with one or more features of the variousembodiments described above or below throughout all the description, the film or sheet isadhered or cast onto substrate which may be either transparent, translucent or opaque.In a more particular embodiment, the substrate is a transparent material, more particularlythe material is glass or a plastic material, such as acrylate-based, polycarbonate,polyurethane, polyesther (PET). If there is refractive index matching between the film orsheet and the substrate, the light passes to the substrate and the substrate acts as anoptical guide to the edges. Also, in this case the cell is positioned on the substrate. Inanother more particular embodiment, the substrate is an opaque material.In one embodiment, optionally in combination with one or more features of the variousembodiments described above or below throughout all the description, the substrate is anadhesive substrate, which has one side coated with the LSC film or sheet and the otherwith adhesive properties to be able to be adhered to another surface. The whole film orsheet becomes an adhesive LSC that can be adhered to glass or plastic substrates.In another embodiment, optionally in combination with one or more features of the variousembodiments described above or below throughout all the description, the film or sheet isan adhesive film or sheet and is attached to substrate by adhesion.In another embodiment, optionally in combination with one or more features of the variousembodiments described above or below throughout all the description, the film or sheet isformed directly on top of the substrate, by casting method.In another embodiment, optionally in combination with one or more features of the variousembodiments described above or below throughout all the description, the film or sheet isplaced between two substrates, more particularly, the two substrates are transparentmaterials such as glass or a plastic material as defined above. Placing the film or sheetbetween two substrates has the advantage that the film or sheet is protected frommechanical, chemical degradation and humidity.In another embodiment, optionally in combination with one or more features of the variousembodiments described above or below throughout all the description, the film or sheet isplaced between two substrates, being one of them opaque or translucid. In another embodiment, optionally in combination with one or more features of the variousembodiments described above or below throughout all the description, the film or sheet isa rigid or a flexible film or sheet.In another embodiment, optionally in combination with one or more features of the variousembodiments described above or below throughout all the description, the film or sheet isflat, slightly bent or curved.The film or sheets of the second aspect may optionally comprise one or more transparentexcipients. The appropriate excipients and their amounts can be readily determined bythose skilled in the art according to the type of material being prepared. Any excipientsmay be used provided that they are transparent and / or match with the refractive index ofthe polymer matrix and / or are soluble in the oil / PCM.The preparation of the films or sheets can be carried out by methods known in the art.Commonly, the preparation of films or sheets implies the use of extrusion, elongation,injection-moulding, casting, in-situ polymerization, spray coating, spin-coating, Dr-Bladecoating, and roll-to-roll coating. The film or sheet may be removed from the substrate, forexample, by peeling off the film or sheet or dissolving the substrate. The film or sheet canbe thermoconformed by heating it above the glass transition temperature, with thesubstrate mould to provide the film or sheet with curved shapes.It also forms part of the invention a process for the preparation of the film or sheet of thesecond aspect which comprises:i) mixing one or more oils or one or more PCMs with optionally one or more luminescentdyes and then mixing the resulting mixture with an aqueous solution of one or more water- soluble polymers,ii) emulsifying the mixture of step (i) to obtain an emulsion,iii) casting the emulsion of step (ii) onto a support, andiv) obtaining a film or sheet by solvent evaporation at an appropriate temperature, inparticular from 30 to 90 ºC, more particularly from 30 to 60 ºC.When the film or sheet is a free-standing film or sheet, the above process furthercomprises a step (v) of separating the film or sheet from the support for example bypeeling it off.When the film or sheet is cast onto a substrate such as another transparent material (i.e.,is adhered to it), the desired transparent material is used as the support of step (iii). In oneembodiment, optionally in combination with one or more features of the various embodiments described above or below throughout all the description, step (iii) is carriedout by depositing the oil emulsion or PCM suspension onto one extreme of the support,and spreading it, particularly by blade coating, thus creating a homogeneous layer of emulsion along the support.Step (iv) may be carried out by drying the support containing the emulsion at a suitabletemperature, e.g. at about 35 °C until the film or sheet is formed (e.g.48 hours), or at atemperature about 50 ºC where the film or sheet is formed within minutes.In one embodiment, optionally in combination with one or more features of the variousembodiments described above or below throughout all the description, the film or sheet iscast onto adhesive substrate, which has one side coated with the LSC film or sheet andthe other with adhesive properties. The whole film or sheet becomes an adhesive LSCthat can be adhered to glass or plastic substrates. In one embodiment, optionally in combination with one or more features of the various embodiments described above or below throughout all the description, the at least one photoactive component capable of converting light into electrical energy as defined in the first or the second aspect is at least one photovoltaic or photoelectrolytic cell. In a particular embodiment, optionally in combination with one or more features of the various embodiments described above or below throughout all the description, the at least one photoactive component capable of converting light into electrical energy, particularly at least one photovoltaic or photoelectrolytic cell, whose absorption matches with theemission of the LSCs, is placed at least at one of the edges of the LSC.The LSC of the present invention may have any suitable shape. Non-limiting examples of the LSC shape include circular or rectangular forms.As mentioned above, the LSC may comprise a polymeric matrix capable of directing lightto the photoactive component, or alternatively, a substrate onto which a film or sheet ofthe polymeric matrix is adhered or cast, wherein the polymeric matrix, the film or sheetthereof, or the substrate comprising the film or sheet, are capable of directing light to thephotoactive component, and the polymeric matrix comprises the nanodroplets ornanocapsules capable of absorbing and / or scattering the light. The reemitted and / orscattered light is directed to the photoactive component through the internal reflectionwithin the thickness of the device. In one embodiment, optionally in combination with one or more features of the various embodiments described above or below throughout all the description, the LSC comprisesa polymeric matrix capable of absorbing and / or scattering the light, and the reemittedand / or scattered light is sent to the photoactive component through the internal reflectionwithin the thickness of the device. More particularly, the thickness of the LSC in thisembodiment is from 5 to 10000 µm, and more particularly from 50 to 5000 µm. A particular embodiment of this LSC is illustrated in FIG.10 and FIG.11. In another embodiment, optionally in combination with one or more features of the various embodiments described above or below throughout all the description, the LSC comprisesa substrate onto which a film or sheet is adhered or cast, and the film or sheet comprisesthe polymeric matrix capable of absorbing and / or scattering the incident light and thereemitted and / or scattered light is directed to the photoactive component through theinternal reflection within the thickness of the device. In a more particular embodiment, the LSC comprises a scattering and / or absorbing layer onto which incident light is scatteredand / or absorbed and the reemitted and / or scattered light is waveguided to the edgesthrough internal reflection. More particularly, the thickness of the LSC of this embodiment comprising both the substrate and the sheet or film is from 5 to 10000 µm, and more particularly from 50 to 5000 µm. A more particular embodiment of this LSC is illustrated in FIG.12.In another embodiment, optionally in combination with one or more features of the variousembodiments described above or below throughout all the description, the LSC as definedin the first or second aspect comprises a polymeric matrix in the absence of any dyes, andthe incident light is scattered to at least some extent and is trapped within the LSC thickness and waveguided to the edges of the LSCs by the total reflection phenomenon, where a photoactive component capable of converting light into electrical energy is attached. In another embodiment, optionally in combination with one or more features of the various embodiments described above or below throughout all the description, the LSC as defined in the first or second aspect comprises a polymeric matrix which comprises one or moreluminescent dyes, particularly one or more luminescent dyes encapsulated in thenanodroplets, and the incident light is absorbed by the dyes, the light emitted by theluminescent dyes is trapped within the LSC thickness and waveguided to the edges of the LSCs by the total reflection phenomenon, where a photoactive component capable of converting light into electrical energy is attached.In another embodiment, optionally in combination with one or more features of the variousembodiments described above or below throughout all the description, the photoactive component at least partially surrounds the perimeter of the LSC, i.e., it covers at least a portion of the perimeter. In another embodiment, optionally in combination with one or more features of the various embodiments described above or below throughout all the description, the photoactive component surrounds the entire perimeter of the LSC, thereby forming a frame around the LSC. In another embodiment, optionally in combination with one or more features of the various embodiments described above or below throughout all the description, the photoactive component has a height that is substantially equal to the thickness of the LSC.In another embodiment, optionally in combination with one or more features of the variousembodiments described above or below throughout all the description, the photoactive component is attached to (i.e. is in contact with) the LSC. In one more particular embodiment, particularly when the thickness of the LSC is from 1000 to 10000 µm, the photoactive component is perpendicularly attached to the scattering and / or absorbing surface of the LSC, in the edges as illustrated in FIG.10-FIG.12. In another more particular embodiment, particularly when the thickness of the LSC is from1 to 1000 µm, the photoactive component is positioned parallel to the scattering and / orabsorbing surface of the LSC on the sides of the surface of the LSC as illustrated in FIG. 13.A third aspect of the invention relates to a construction element comprising one or moresolar devices as previously defined. Non-limiting examples of construction elementsinclude building windows, automobile glasses, greenhouse envelopes, sunroofs, skylights,and facades of commercial and residential buildings, and the like. Throughout the description and claims the word "comprise" and variations of the word, are not intended to exclude other technical features, additives, components, or steps. Furthermore, the word “comprise” encompasses the case of “consisting of”. Additional objects, advantages and features of the invention will become apparent to those skilled in the art upon examination of the description or may be learned by practice of the invention. The following examples and drawings are provided by way of illustration, and they are not intended to be limiting of the present invention. Furthermore, the present invention covers all possible combinations of particular and preferred embodiments described herein. Examples Dyes: 9,10-diphenyl anthracene (DPA), with absorption maximum at λmax = 373 nm and emission maximum at λmax = 405 nm.9,10-bis(phenylethynyl)anthracene (BPEA) (Alfa Aesar), with absorption maximum at ^max= 463 nm, and emission maximum at ^max = 470 nm.N,N’-bis(3-pentyl)perylene-3,4,9,10-bis(dicarboximide) (PDI) (Alfa Aesar), with absorptionmaximum at ^max = 521 nm, and emission maximum at ^max = 525 nm. Pt(II) octaethylporphyrin (PtOEP), with absorption maximum at 381 nm (Q band) nm and534 nm (Soret band), and emission maximum at ^max = 645 nm.General preparation procedures:1. Nanoemulsions / suspensions preparationa. Oil nanoemulsionsThis procedure applies to all oil-based films, with and without dyes.0.8 g of Miglyol 812 (Sasol) mixture (with / without dye) and 5 g of H2O were added to a vialcontaining 15 g aqueous solution of PVA 4-8820 wt.%. The mixture was stirred to homogenize and then sonicated during 4 cycles of 10 minutes, at an amplitude of 70%.When dyes were used, these were added in the initial oil solution (10-4 – 10-2 M).b. PCM suspensionsThis procedure applies to all PCM-based films, with and without dyes. PCM emulsion was prepared by adding 1 g of eicosane (EC) (Alfa Aesar) (at a temperature above the PCM melting point, 37 °C) to 20 g of aqueous solution of PVA 4-88 10 wt.%. The mixture was ultrasonicated for 5 minutes operating at 70% amplitude. When dyes were used, these were added in the initial PCM melt (1-3 mg / g of PCM).2. Luminescent solar concentratorsa. Self-standing filmsFrom oil nanoemulsions 6 g of oil-nanoemulsion were cast onto a plastic petri of 5.2 cm of internal diameter. The solid film was obtained via solvent evaporation leaving the film with the nanoemulsion at 35 °C for 48 hours. Once the film formed, it was easily peeled off from the mould. From PCM suspensions All PCM-based films were prepared in the same way, but more diluted.5 g of nanoemulsion in 1.7 g of H2O or 1 g of emulsion in 6 g of PVA 4-8810 wt.% and 1.2 g of H2O or 7.5g of emulsion and 2.5 g H2O. These solutions, after homogenized, were poured onto a polypropylene petri plate, and dried through solvent evaporation, as explained above.b. Glass slide coated with the filmGlass slides-based LSC were obtained by depositing the oil nanoemulsion or the PCM suspensions in one extreme of the slide, and its spreading with a Dr Blade Zehntner ZAA2300.FH at a constant velocity, creating a homogeneous layer of emulsion along the slide. The film layer was obtained after 24 h at 35 °C on a flat surface upon solvent evaporation. Examples description1. Dyeless filmsA dyeless film (480 µm thickness) according to the invention and prepared by the procedures described above (Example 1) is shown in Table 1. As comparison, plain filmsof polymethyl methacrylate (PMMA) and PVA without nanodroplets (Examples 2-3) werealso prepared. Table 1 [dye] in Oil conc. Conc. dye λmemirDye Oilthe oil in film in the film Droplet λmabsaxExample Polymeax t.%) size (nm)* edges (M) (wt.%) (w (nm) (nm) 1PVA none Miglyol812 -- 21 -- ≤213 --450, 532, 589, 650 2PMMA none None -- -- -- -- -- None3 PVA none None -- -- -- -- -- None* According to Dynamic Light Scattering (DLS) analysisThe film of Example 1 was flexible and very transparent (FIG.1a), with %T > 80% atwavelengths above 400 nm and 550 nm (FIG.1b). The films of Examples 1 and 2 wereirradiated by 4 different monochromatic lights (450 nm, 532 nm, 590 nm, 650 nm). As canbe seen in FIG. 2, for the film according to the invention the monochromatic scattered lightwas guided and measured in the edges in all cases. By contrast, for the comparative PMMA film without nanodroplets of Example 2 no emission was observed at the edges (FIG.2a). Moreover, when the film according to the invention was irradiated with polychromatic solar simulator light source, the broadband emission of the source was also guided to the edges. Further, when the films were exposed to a Xe lamp (whose emission spectrum is represented in FIG.3a) it was seen that its emission was redirected to the edges of the nanodroplets-containing film of Example 1 (FIG 3b). As comparison, plain films of PMMA and PVA (Examples 2-3), without nanodroplets, did not show any LSC property as no Xe light emission was detected in the edges of these films.2. Single-dye containing filmsSingle-dye containing films (480 µm thickness) according to the invention and prepared as described above are shown in Table 2: Table 2 Conc. Example Dye Oil[dye] in Oil conc. in dye in th Droplet λmaxabsλmaxemithe oil (M) film (wt.%) e film (wt.%) size (nm) (nm) edges (nm) 4DPA Miglyol812 10-2 21 0.25 ≤213 373 4055 BPEA Miglyol812 10-4 21 0.003 ≤213 463 4706 PDI Miglyol812 10-4 21 0.004 ≤213 521 5257 PtOEP Miglyol812 10-4 21 0.006 ≤213 381 & 534 645* According to Dynamic Light Scattering (DLS) analysis In all cases, emission in the edges was obtained (FIG.4). The emission spectra measured resembled those of the dyes in their bulk solutions, indicating that the dyes preserved the emission properties once integrated in the films through the nanodroplets. Noticeably the phosphorescence emission of the nanodroplets-containing film made with PtOEP (FIG.4 d) could be observed in air atmosphere, corroborating the oxygen barrier effect of the PVA.3. Multiple-dye containing films (energy-transfer films)Multiple-dye containing films according to the invention and prepared as described aboveare shown in Tables 3-5.a. Dye-pairs undergoing Förster Resonance Energy Transfer (FRET)As example for FRET process, BPEA (energy donor) and PDI (energy acceptor) were used, as the emission spectrum of BPEA overlaps well with the absorption spectrum of PDI.Different self-standing films were prepared as above. One film (480 μm thickness) wasobtained from a nanoemulsion in which the oil contained both dyes (Example 8). Two films were obtained by mixing two nanoemulsions each one containing one type of dye (Examples 9-10). This experiment was carried out to show that the energy transferbetween the donor and the acceptor was through FRET (only possible through closeinteraction within the same nanodroplets) and not through light reabsorption (possible also at longer distance). The last two films were used as blank. Table 3 Solution do Conc. BPEAConc. PDIExample Dyes Oil conc. in nor Solution acceptor distribution film (wt.%)concentration in concentration indye in the dye in the oil [BPEA] (M) oil [PDI] (M)film film (wt.%) (wt.%) 8 In the same-4droplet21 10 10-4 0.003 0.0049 Dyes in different droplets10.5 + 10.5 10-4 10-4 0.0015 0.00210 Dyes in different droplets10.5 + 10.5 2*10-4 2*10-4 0.003 0.004The following results allowed to confirm the presence of FRET between the donor and theacceptor (FIG.5).^ In Example 8 the BPEA emission was fully quenched as a consequence of the energytransfer to the PDI.^ PDI emission intensity was enhanced compared to the film obtained with only PDI,due to the FRET contribution to its excitation.^ Films obtained from dyes in different nanodroplets (Examples 9-10) showed thepresence of the BPEA emission as it was not quenched through FRET.b. Dye-pairs undergoing Upconversion through triplet-triplet energy transfer (TTA-UC)The second example involving dye pairs was the upconversion (UC), through triplet-tripletenergy transfer. In upconversion a low-energy irradiation, should yield a higher energy irradiation. The overall process involves several bimolecular processes. The pair chosen for UC was made by PtOEP as triplet sensitizer and DPA as triplet acceptor and annihilator (emitter). This pair is expected to produce blue upconverted (UC) emission from DPA.A self-standing film (480 μm thickness) was prepared as above (Example 11). Also a filmwas prepared on top of a glass slide (Example 12). As comparison, a PMMA film was prepared without the nanodroplets technology and embedding the dyes directly in the matrix (Example 13), i.e. no dyes diffusion is expected. Table 4 Oil soluti Conc. Conc. Oil conc. Oil sol on Dyes ution donor acc DPA dye PtOEPemiEx Support in film concentr eptor λmax distrib. ation concentr in the dye in (wt.%) [PtOEP] (M) ation film th edges [DPA] (M) e film (wt.%) (wt.%) (nm) In the 11 same Self-standing fil21 10-4 10-2 0.25 0.006435 & droplet m 650 In the 12 sameGlass slide 21 10-4 10-2 0.25 0.006435 & droplet 650 In the 13 PMMA Self-standing film-- -- -- 0.22 0.005 650matrix* * This PMMA film was prepared dissolving directly PMMA and the dyes in chloroform under magnetic stirring and then letting the solvent to evaporate. Then, calculated amount of dyes (7.8510-8mol) were added to the solution and once mixed, cast to a Petri. Dyes amount were calculated to have the same concentration as in M812@PVA. The transparent film of Example 11 showed upconverted blue light in the irradiated pointand mixed red (phosphorescence) and blue (UC) emission in the edges (FIG.6).When the film was prepared on top of a glass slide, the glass showed upconverted bluelight in its edges, under laser light (532 nm, 1.2 mW / cm2) (Example 12). The emissionpassed from the film to the glass thanks to the refractive index matching. In this way the self-absorption of the DPA was eliminated (FIG.7, FIG.8). As a reference, the comparative PMMA films without nanodroplets of Example 13 and embedding the dyes directly in the matrix did not show any upconverted emission, due to the inhibition of the molecular diffusion, and showed instead only the emission of the phosphorescence ofPtOEP (FIG. 8).4. Dynamic LSCs For the dynamic LSCs, oil was substituted by PCM. As a dye PDI was used as it is known to produce excimer emission in the solid PCM and monomer emission in the liquid EC. Two self-standing films (480 μm thickness) were prepared using different concentrations of the dye in the PCM (Example 14-15). In the lower concentrated film, the emission at the edges varied from low-intensity excimer emission (λem = 610 nm), to high-intensity monomer emission (λem = 525 nm) upon heating (and melting the PCM nanoparticles in the film). In the more concentrated film, the transition was from a reddish / orange emission (λem = 610 nm) to a monomer greenish emission (λem = 525 nm), passing from 25ºC to 50ºC. The spectral changes over the temperature variation are shown in FIG.9.Table 5 [dye] in PCM conc. Concemi emiample Dye Oilt . dye λmax λmaxExhe PCM Droplet (mg PDI / g In film in the film (nm) (nm) (wt. size (nm) EC) %) (wt.%) Low T High T 14 PDI Eicosane 2 33 0.07 ≤400 610 (low) 52515 PDI Eicosane 2.5 33 0.08 ≤400 610 575Citation List- Dias et al., “Uncovering the use of Fucoxanthin and Phycobiliproteins into solid matricesto increase their emission quantum yield and photostability”, Applied Sciences 2022, 12, 5839.- Congiu et al, “Microemulsions for luminescent solar concentrator application”, SolarEnergy 2021, 216, 338–350. For reasons of completeness, various aspects of the invention are set out in the following numbered clauses: Clause 1. Use of a polymeric matrix for generating electricity, wherein the polymeric matrix comprises: a) a water-soluble polymer, and b) nanodroplets dispersed in the water-soluble polymer which comprise: i) one or more oils, or alternativelyii) one or more phase change materials (PCMs), or alternatively iii) one or more oils and one or more phase change materials (PCMs).Clause 2. Use according to clause 1, wherein the water-soluble polymer is transparentand is selected from the group consisting of polyvinyl alcohol (PVA), a cellulose ether,polyvinylpyrrolidone (PVP), and a combination thereof.Clause 3. Use according to any of the clauses 1-2, wherein the water-soluble polymer ispresent in an amount from 50 to 95% by weight with respect to the total matrix weight.Clause 4. Use according to any of the clauses 1-3, wherein the nanodroplets whichcomprise one or more oils or one or more PCMs are present in an amount from 5 to 50%by weight with respect to the total matrix weight.Clause 5. Use according to any of the clauses 1-4, wherein the nanodroplets compriseeither one or more oils, or alternatively one or more PCMs, and have a diameter from 10to 400 nm. Clause 6. Use according to any of the clauses 1-5, wherein the nanodroplets comprise one or more oils selected from the group consisting of caprylic / capric triglyceride oil (Miglyol® 812), caprylic / capric / succinic triglyceride oil (Miglyol® 829), diisodecyl adipate, diethylhexyl sebacate, dioctyl sebacate, and a combination thereof. Clause 7. Use according to any of the clauses 1-5, wherein the nanodroplets comprise one or more phase change materials (PCMs) selected from the group consisting of (C8-C52)alkanes, (C1-C30)alkyl-COOH, (C1-C30)alkyl-COO-(C1-C30)alkyl, (C1-C30)alkyl-OH, (C1-C30)alkyl-O-(C1-C30)alkyl, (C1-C20)alkyl-NH-(C1-C20)alkyl, (C1-C20)alkyl-N-((C1- C20)alkyl)2, and a combination thereof. Clause 8. Use according to any of the clauses 1-7, wherein the nanodroplets further comprise one or more luminescent dyes. Clause 9. Use according to any of the clauses 1-8, wherein the nanodroplets comprising one or more oils and / or one or more PCMs are in the form of capsules.Clause 10. Use of a film or sheet or a substrate onto which the film or sheet is adhered orcast for generating electricity, wherein the film or sheet comprises the polymeric matrix asdefined in any of the clauses 1-9 and optionally one or more transparent excipients.Clause 11. Use according to clause 10, wherein the substrate is an adhesive substrate,which has one side coated with the film or sheet and the other with adhesive properties to be able to be adhered to another surface. Clause 12. Use of the polymeric matrix as defined in any of the clauses 1-9 or alternatively the film or sheet or substrate onto which the film or sheet is adhered or castas defined in any of the clauses 10-11, as a luminescent solar concentrator (LSC).Clause 13. A solar device comprising the LSC as defined in clause 12 and at least onephotovoltaic or photoelectrolytic cell.Clause 14. A construction element comprising one or more solar devices as defined in inclause 13.Clause 15. A method for generating electricity which comprises the step of exposing asolar device as defined in clause 13 to sunlight, whereby the polymeric matrix as definedin any of the clauses 1-10, or alternatively the film or sheet or substrate onto which thefilm or sheet is adhered or cast as defined in clause 11 is capable of concentrating thesunlight on the at least one edge where photovoltaic or photoelectrolytic cell is mounted,and the concentrated light is converted into electricity.

Claims

Claims 1. A solar device comprising a luminescent solar concentrator (LSC), and at least one photoactive component capable of converting light into electrical energy, wherein theluminescent solar concentrator comprises a polymeric matrix capable of directing light tothe photoactive component, wherein the polymeric matrix comprises:a) a water-soluble polymer, andb) nanodroplets dispersed in the water-soluble polymer which comprise: i) one or more oils, or alternativelyii) one or more phase change materials (PCMs), or alternativelyiii) one or more oils and one or more phase change materials (PCMs).

2. The solar device according to claim 1, wherein the water-soluble polymer is transparentand is selected from the group consisting of polyvinyl alcohol (PVA), a cellulose ether,polyvinylpyrrolidone (PVP), and a combination thereof.

3. The solar device according to any of the claims 1-2, wherein the water-soluble polymeris present in an amount from 50 to 95% by weight with respect to the total matrix weight.

4. The solar device according to any of the claims 1-3, wherein the nanodroplets whichcomprise one or more oils or one or more PCMs are present in an amount from 5 to 50%by weight with respect to the total matrix weight.

5. The solar device according to any of the claims 1-4, wherein the nanodroplets compriseeither one or more oils, or alternatively one or more PCMs, and have a diameter from 10to 400 nm.

6. The solar device according to any of the claims 1-5, wherein the nanodroplets compriseone or more oils selected from the group consisting of caprylic / capric triglyceride oil(Miglyol® 812), caprylic / capric / succinic triglyceride oil (Miglyol® 829), diisodecyl adipate, diethylhexyl sebacate, dioctyl sebacate, and a combination thereof.

7. The solar device according to any of the claims 1-5, wherein the nanodroplets compriseone or more phase change materials (PCMs) selected from the group consisting of(C8-C52)alkanes, (C1-C30)alkyl-COOH, (C1-C30)alkyl-COO-(C1-C30)alkyl, (C1-C30)alkyl-OH, (C1-C30)alkyl-O-(C1-C30)alkyl, (C1-C20)alkyl-NH-(C1-C20)alkyl, (C1-C20)alkyl-N-((C1- C20)alkyl)2, and a combination thereof.

8. The solar device according to any of the claims 1-7, wherein the nanodroplets furthercomprise one or more luminescent dyes.

9. The solar device according to any of the claims 1-8, wherein the nanodroplets comprising one or more oils and / or one or more PCMs are in the form of capsules.

10. The solar device as defined in any of the claims 1-9, wherein the nanodroplets arecapable of concentrating light to at least one of the edges of the polymeric matrix.

11. A solar device comprising a luminescent solar concentrator (LSC), and at least one photoactive component capable of converting light into electrical energy, wherein the luminescent solar concentrator comprises: A) a film or sheet, or B) a substrate onto which the film or sheet is adhered or cast; wherein the film or sheet A), or the substrate comprising the film or sheet B), are capable of directing light to the photoactive component, and wherein the film or sheet A) comprises the polymeric matrix as defined in any of the claims 1-10, and optionally one or more transparent excipients.

12. The solar device according to claim 11, wherein the substrate is an adhesivesubstrate, which has one side coated with the film or sheet and the other with adhesiveproperties to be able to be adhered to another surface.

13. The solar device as defined in any of the claims 1-12, wherein the at least onephotoactive component capable of converting light into electrical energy is at least onephotovoltaic or photoelectrolytic cell.

14. A construction element comprising one or more solar devices as defined in any of theclaims 1-13.

15. A method for generating electricity which comprises the step of exposing the solardevice as defined in any of the claim 1-13 or the construction element as defined in claim14 to sunlight, whereby the polymeric matrix directs the sunlight to the photoactivecomponent, and the photoactive component converts the concentrated light intoelectricity.

Images