Active low-e transparent structure

Abstract

An active low-e transparent structure (1), in particular for building-integrated photovoltaics applications, comprising a transparent substrate (70) on which at least a first layered structure (20) is arranged; said layered structure (20) comprises: a superlattice film (80) consisting of a superlattice structure (10) sandwiched between a first dielectric layer (81) and a second dielectric layer (82) and two transparent conductor layers (91, 92), between which said superlattice film (80) is sandwiched; Said superlattice structure (10) comprises a plurality of superimposed layers of nanocrystals and is configured to generate a flow of electrons across said layers when it is irradiated by solar radiation (S).

Description

[0001] ACTIVE LOW-E TRANSPARENT STRUCTURE

[0002] D E S C R I P T I O N

[0003] The present invention relates to an active low-e transparent structure which is useful, in particular, but not exclusively, for building-integrated photovoltaic (BIPV) applications.

[0004] Background of the Invention

[0005] Building-integrated photovoltaic (BIPV) applications encompass the use of photovoltaic materials and products in parts of buildings, especially in the building envelope such as the roof, windows, skylights, walls, fagades etc. In fact, photovoltaic materials and products are increasingly being incorporated into the construction of new buildings as a principal or ancillary source of electrical power, while existing buildings can be retrofitted with similar technology. The advantage of integrated photovoltaics over more common nonintegrated systems is that the initial cost can be offset by reducing the amount spent on building materials and labor that would normally be used to construct the part of the building that the BIPV modules replace. In addition, BIPV applications allow for more widespread solar adoption when the building's aesthetics take priority and traditional rack-mounted solar panels would disrupt the intended look of the building. However, the known photovoltaic technologies generally require additional scaffoldings and frames to hold the photovoltaic devices.

[0006] In the field of building integrated photovoltaics , it is known to use thin-film solar cells on exposed surfaces of a building in order to generate energy.

[0007] Usually, thin-film solar cells are made by depositing one or more thin layers (thin films or TFs) of photovoltaic material onto a substrate, such as glass, plastic, or metal. Thin-film solar cells are typically a few nanometers (nm) to a few microns (pm) thick. Thin-film solar cells can be based on several different technologies, including cadmium telluride (CdTe) , copper indium gallium diselenide (CIGS) , and amorphous thin-film silicon (a-Si, TF-Si) .

[0008] In this context, it is known to use transparent see-through Cadmium Telluride (CdTe) thin-film solar cells to make transparent solar photovoltaic glass by depositing this type of thin-film on the glass.

[0009] However, such known photovoltaic glass does not provide any advantage in terms of thermal performance.

[0010] In fact, the thin-films used in the known types of photovoltaic glass do not contribute to lowering the emissivity of the glass ( i . e . the ability of the glass to radiate energy) .

[0011] For this purpose , low-e ( low-emissivity) types of glass are known, which are types of clear glass that have been treated with a thin coating to minimi ze the amount of ultraviolet and / or infrared light that can pass through the glass without compromising the amount of visible light that is transmitted . The coating also improves the insulating properties of the glass . Low-e glass plays a very important role in buildings that have facades comprising large expanses of glass .

[0012] By reflecting radiant energy, low-e glass can reduce the radiative heat trans fer, thereby reducing the thermal transmittance (U-value ) of windows .

[0013] Generally, low-e coatings have low emissivity in the infrared and / or UV wavelength range and high transmittance in the visible range ; moreover, these coatings have a low luminous reflectance and preferably are essentially colorless ( for most applications but the decisions of the architect may result in other speci fications ) . Low-e coatings , in practice , generally comprise ultrathin metallic layers , in particular Ag, for infrared reflectance and low emissivity, alternated with dielectric layers of metal oxides with di f ferent refractive indices to reduce the visible reflectance .

[0014] Adhesion layers and / or protection layers are also commonly applied to ensure the durability of the coatings .

[0015] Windows with low-e glass can reduce energy loss signi ficantly . However, the known types of low-e glass do not have photovoltaic properties .

[0016] Therefore , in the state of the art , the only way to have a glass that has both low-e and photovoltaic properties consists in stacking a thin- film solar cell on top of low-e glass , in practice producing a glass with two di f ferent coatings : one for reducing emissivity and one for producing energy . Obviously, this solution is complex, di f ficult to manufacture , costly, and not cost-ef fective . Besides , such double coating can compromise the transparency and the aesthetic of the glass .

[0017] Summary of the Invention

[0018] The aim of the present invention is to solve the technical problem described above , obviating the drawbacks and overcoming the limitations of the background art , by providing an active low-e transparent structure that has both photovoltaic and low-e properties and thus can be used in place of a low-e glass to also produce anergy .

[0019] Within the scope of this aim, an obj ect of the invention is to provide an active low-e transparent structure that is easy to manufacture and at low costs .

[0020] A further obj ect of the present invention is to provide an active low-e transparent structure that has higher ef ficiency when compared to structures based on known thin- film solar cells .

[0021] Moreover, an obj ect of the present invention is to provide an active low-e transparent structure that is highly versatile and thus can be used in di f ferent applications other than as glass for windows and facades .

[0022] Another obj ect of the present invention is to also provide an alternative to known solutions .

[0023] This aim, as well as these and other obj ects that will become better apparent hereinafter, are achieved by an active low-e transparent structure , in particular for building-integrated photovoltaics applications , comprising a transparent substrate on which at least a first layered structure is arranged, said layered structure comprising : a superlattice film consisting of a superlattice structure sandwiched between a first dielectric layer and a second dielectric layer ;

[0024] - two transparent conductor layers , between which said superlattice film is sandwiched; wherein said superlattice structure comprises a plurality of superimposed layers of nanocrystals and is configured to generate a flow of electrons across said layers when it is irradiated by solar radiation .

[0025] This aim and these obj ects are also achieved by a method of making an active low-e transparent structure , comprising at least the steps of : a ) depositing a first transparent conductor layer on transparent substrate ; b ) depositing a first dielectric layer on said first transparent conductor layer ; c ) depositing a superlattice structure comprising a plurality of superimposed layers of nanocrystals on said first dielectric layer ; d) depositing a second dielectric layer on said superlattice structure ; e ) depositing a second transparent conductor layer on said second dielectric layer ; wherein said superlattice structure is configured to generate a flow of electrons across said layers when it is irradiated by solar radiation .

[0026] Brief Description of the Drawings

[0027] The foregoing, as well as further characteristics and advantages of the present invention, will become better apparent from the following description of some preferred, but not exclusive , embodiments of an active low-e transparent structure , according to the invention, illustrated by way of non-limiting example in the accompanying drawings wherein :

[0028] Figure 1 is a schematic representation of a photovoltaic device comprising an active low-e transparent structure according to the invention;

[0029] Figure 2 is a schematic representation of the active low-e transparent structure of Figure 1 , wherein the internal structure of the superlattice structure is visible ;

[0030] Figure 3 is a schematic representation of the functioning of the active low-e transparent structure of Figure 2 ;

[0031] Figure 4 is a schematic representation of the superlattice structure included in the active low-e transparent structure ;

[0032] Figure 5 is a schematic representation of an alternative superlattice structure that can be included in the active low-e transparent structure ;

[0033] Figure 6 is a schematic representation of a photovoltaic device comprising a first alternative embodiment of the active low-e transparent structure according to the invention;

[0034] Figure 7 is a schematic representation of the active low-e transparent structure of Figure 6 , wherein the internal structure of the superlattice structure is visible ;

[0035] Figure 8 is a schematic representation of a photovoltaic device comprising a second alternative embodiment of the active low-e transparent structure according to the invention;

[0036] Figure 9 is a schematic representation of the active low-e transparent structure of Figure 8 , wherein the internal structure of the superlattice structure is visible .

[0037] It should be noted that the above-mentioned drawings should be understood as being schematic, since they do not reflect the exact proportions , in order to better show the underlying structure of the invention . For example , in Figures 2 , 3 , 7 and 9 , the thickness of the layer that constitutes the superlattice structure has been exaggerated to show the layers of nanocrystal included therein .

[0038] Detailed Description of the Invention

[0039] With reference to the cited figures , the active low-e transparent structure , generally designated by the reference numeral 1 ( or 1A, or IB, for the alternative embodiments ) , comprises a transparent substrate 70 on which at least a first layered structure 20 is arranged ( in practice , deposited) .

[0040] It is useful to clari fy that , in the present description and in the attached claims :

[0041] - "transparent" means transparent to at least part of visible light , i . e . an element is considered transparent when it is possible to at least partially see through it , at least from one side ;

[0042] - " low-e" means low-emissivity in the sense that the structure 1 , 1A, IB has a reduced emissivity, and thus a lower thermal transmittance (U-value ) , than the transparent substrate 70 taken alone ;

[0043] - "active" means that the structure 1 , 1A, IB has the ability to generate / convert energy, in particular that it has photovoltaic properties .

[0044] The layered structure 20 comprises a superlattice film 80 that consists of a superlattice structure 10 sandwiched between a first dielectric layer 81 and a second dielectric layer 82.

[0045] The layered structure 20 further comprises two transparent conductor layers 91, 92, between which the superlattice film 80 is sandwiched.

[0046] In other words, the layered structure 20 is composed at least of the following layers 91, 81, 10, 82, 92 directly stacked on each other in that order: a first transparent conductor layer 91, a first dielectric layer 81, a superlattice structure 10, a second dielectric layer 82, and a second transparent conductor layer 92.

[0047] All the layers 91, 81, 10, 82, 92 (including the superlattice structure 10, 10A) which form the layered structure 20 are transparent. This means that the materials and thickness of the layers are chosen so that the layered structure 20 is transparent.

[0048] Advantageously, within the layered structure 20, each layer 91, 81, 10, 82, 92 has a refractive index that is different from the refractive index of the underlying layer, so that the interfaces between the layers provide a reflectiveness for a predetermined wavelength range (in particular for UV) , while allowing visible light to pass through.

[0049] The superlattice structure 10, 10A comprises a plurality of superimposed layers 4A-4L (or 2A-2E and

[0050] 3A-3D in Figure 5) of nanocrystals 41-50 (or 21-25 and 31-34 in Figure 5) and is configured to generate a flow of electrons e~ across said layers (4A-4L, 2A-2E, 3A- 3D) when it is irradiated by solar radiation S.

[0051] Each of the layers 4A-4L, 2A-2E, 3A-3D of the superlattice structure 10, 10A comprises an array of nanocrystals 41-50, 21-25, 31-34 which have the same energy gap (as is known, the energy gap in a nanocrystal is the energy difference between the bottom of the conduction band and the top of the valence band of the electrons) .

[0052] In practice, to have the same energy gap, all the nanocrystals of a same layer 4A-4L, 2A-2E, 3A-3D have the same size and shape. It is useful to specify that the term "shape", in the present description and in the attached claims, is understood to reference the mere geometry (i.e. the geometric structure) of a nanocrystal, regardless of its size.

[0053] In the superlattice structure 10, 10A, the layers 2A-2L, 3A-3L, 4A-4L are sorted by the energy gap of the nanocrystals 41-50, 21-25, 31-34 in ascending order from the first dielectric layer 81 towards the second dielectric layer 82, or vice versa. In other words, the layers 2A-2L, 3A-3L, 4A-4L are sorted in such an order that the energy gap of the nanocrystals 41-50, 21-25, 31-34 increases from the first dielectric layer 81 to the second dielectric layer 82, or vice versa.

[0054] In general, then, all the layers 4A-4L, 2A-2E, 3A- 3E are sorted by the size (i.e. by the volume) of the nanocrystals 21-25, 31-34 in ascending order (along the transverse direction Y along which the electrical conductivity is required) from the first dielectric layer 81 to the second dielectric layer 82, or vice versa .

[0055] In fact, the energy gap in a nanocrystal is inversely proportional to the size (i.e. to the volume) of the nanocrystal.

[0056] It follows that, in the example of figure 2, a maximum energy gap layer 4L (i.e. the layer that comprises the nanocrystals 50 having the maximum energy gap) is adjacent to the second dielectric layer 82 and a minimum energy gap layer 4A (i.e. the layer that comprises the nanocrystal having the minimum energy gap) is adjacent to first dielectric layer 81.

[0057] In this manner, in the superlattice structure 10, 10A, the electrons e~ are induced to flow along the transverse direction Y, from the maximum energy gap layer 4L, 2E towards the minimum energy gap layer 4A,

[0058] 2A and not vice versa.

[0059] In Figures 2, 3, 4, 7, and 9 the nanocrystals are depicted as spherical only for simplicity, to indicate any possible shape: the nanocrystals 41-50 can have any suitable shape, such as hexadecahedronal , pentahedronal , octahedral, cuboctahedral , hexagonal, etc .

[0060] In some embodiments, all the nanocrystals 41-50 contained in the superlattice structure 10, 10A have the same shape, and thus each layer 4A-4L differs from the others only in the size of the nanocrystals 41-50. However, in some alternative embodiments, such as the one depicted in Figure 5, the superlattice structure 10A comprises layers of a first type 2A-2E which comprise nanocrystals having a first shape, and layers of a second type 3A-3D which comprise nanocrystals having a second shape that is different from said first shape; in this case the layers of the first type 2A-2E are alternated with the layers of the second type 3A- 3D.

[0061] As to the composition of the nanocrystals 21-25, 31-34, they are made of semiconductor materials such as: CdS, CdSe, CdTe, InP, InAs, ZnS, ZnSe, HgTe, GaN, GaP, GaAs, GaSb, InSb, Si, Ge, AlAs, AlSb, PbSe, PbS,

[0062] PbTe, InGaAs, InGaN, AlInGaP.

[0063] In the preferred embodiments, the nanocrystals 21- 25, 31-34 are made of one or more of the following materials: PbSe, PbS, PbTe, CdS, CdSe, CdTe.

[0064] Preferably, all the nanocrystals 21-25, 31-34 are made of the same material.

[0065] In practice, the superlattice structure 10, 10A can be any superlattice structure described in WO 2021 / 070169.

[0066] Advantageously, the nanocrystals 41-50 are fixed in predetermined positions within the layers 4A-4L in such a way that they have both an energetic and a mechanical alignment.

[0067] In particular, it should be noted that within the superlattice structure 10, 10A the nanocrystals are fixed in predetermined positions in such a way that they are in energetic alignment. In practice, the energy gaps of the nanocrystals are aligned so as to allow the electrons e~ (excited by absorption of solar radiation S) to traverse the whole superlattice structure 10, 10A.

[0068] It also should be noted that, within the superlattice structure 10, 10A, the nanocrystals 41-50 21-25, 31-34 are fixed in predetermined positions in such a way that they are in shape-directional alignment .

[0069] In greater detail, the shapes and the orientations of the nanocrystals 41-50, 21-25, 31-34 are provided so that the nanocrystals have not only an energetic alignment, but also a mechanical alignment.

[0070] Ultimately, in the preferred embodiments, the nanocrystals 41-50, 21-25, 31-34 are fixed in predetermined positions, within said layers 4A-4L, 2A- 2E, 3A-3E, in such a way that they have both an energetic and a mechanical alignment.

[0071] Advantageously, the gaps and connections between the nanocrystals 21-25, 31-34 are controlled by the Ligand molecules that are connected to the nanocrystals 21-25, 31-34.

[0072] As a result of the synergistic combination of such energetic and mechanical alignment, within the superlattice structure 10, 10A there is a very high probability that an electron e- , excited in a nanocrystal 41-50, 21-25, 31-34 as a result of the absorption of a photon, will "jump" (move) to the nanocrystal 41-50, 21-25, 31-34 that is adjacent in the transverse direction Y towards the first transparent conductor layers 91 (in the illustrated example) , and there is a very low probability that such electron e- will "jump" (move) to the other nanocrystals 41-50, 21-25, 31-34 which are ad acent in the other directions .

[0073] The two transparent conductor layers 91, 92 are configured to be refractive layers and are adapted to be electrically connected so that the layered structure 20 functions as a solar cell.

[0074] Preferably, the transparent conductor layers 91, 92 are made of a transparent conductive oxide, such as ITO or FTO, or of Ag, or Al, or Au.

[0075] Preferably, the dielectric layers 81, 82 are made of a metal oxide and / or of a metal alloy. Examples of materials suitable for these dielectric layers 81, 82 are: TiO2, SnO2, ZnO, NiO, SnZnO, MoOx. More in general, any material that has suitable refractive properties, and that (as explained hereinafter) can be used as ETL or EBL, can be used.

[0076] Advantageously, the first dielectric layer 81 is configured to be an electron transport layer (ETL) and the second dielectric layer 82 is configured to be an electron blocking layer (EBL) , or vice versa.

[0077] As is known, an electron transport layer (also called hole blocking layer (HBL) ) is a layer that has physical properties (such as charge mobility, energy level alignment, defect states, morphology, and related interfacial properties) which make it useful in extracting and transporting excited electron carriers, and it serves as a hole-blocking layer by suppressing charge recombination.

[0078] For example, the first dielectric layer 81, in order to also be an electron transport layer, can be made of one of the following materials: TiCh, SnCh, ZnO, SnO. More in general, any material that has the required refractive properties, and that can be used as ETL, can be used.

[0079] As known, an electron blocking layer (also called hole transport layer (HTL) ) has substantially the opposite effect of the electron transport layer, and reduces the leakage of electrons for instance toward the second transparent conductor layers 92 (in the example of Figure 3) .

[0080] For example, the second dielectric layer 82, in order to also be an electron blocking layer, can be made of one of the following materials: NiO or MoOx. More in general, any material that has the required refractive properties, and that can be used as EBL (HTL) , can be used.

[0081] In greater detail, the layers of nanocrystals 4A- 4L, 2A-2E, 3A-3D are sorted so that the maximum energy gap layer 4L, 2E is adjacent to the dielectric layer 82 which is an electron blocking layer (the second dielectric layer 82 in the illustrated examples) , and the minimum energy gap layer 4A, 2A is adjacent to the dielectric layer 81 which is an electron transport layer (the first dielectric layer 81 in the illustrated examples) .

[0082] Therefore, the dielectric layers 81, 82 have a double function: on the one hand they have the same function as the dielectric layers in the known types of low-e glass (i.e. providing reflectiveness for at least a portion of non-visible light, while allowing visible light to pass through, by virtue of the refractiv index) , and on the other hand they increase the photovoltaic efficiency, allowing the layered structure 20 to act as a solar cell.

[0083] In fact, the presence of the electron transport layer on one side of the superlattice structure 10 and the presence of the electron blocking layer on the other side extends the work function between the transparent conductor layers 91, 92 and the nanocrystals and thus increases the efficiency of the superlattice film 1, 10A, 10B when used as a photovoltaic device 100, 100A, 100B.

[0084] Preferably, each of the dielectric layers 81, 82 has a thickness comprised between 10 nm and 100 nm.

[0085] Preferably, each of the transparent conductor layers 91, 92 has a thickness:

[0086] - comprised between 5 nm and 15 nm, when made of metals such as AU, Ag, Al;

[0087] - comprised between 30 nm and 250 nm, when made of ITO or FTO.

[0088] Preferably, the superlattice structure 10, 10A has a thickness comprised between 20 nm and 150 nm.

[0089] The same sequence of layers (a transparent conductor layer 91, a dielectric layer 81, a superlattice structure 10, a second dielectric layer 82, and a second transparent conductor layer 92) can be repeated one or more times on top of the described first layered structure 20 to form a multi-layered low- e transparent active structure 1A, IB, such as the one illustrated in Figures 6-9.

[0090] In these alternative embodiments, the low-e transparent structure 1A, IB further comprises at least a second superlattice film 80' stacked on top of said first layered structure 20 and sandwiched between said first layered structure 20 and a third transparent conductor layer 92 ' .

[0091] In practice , in the low-e transparent structure 1A, IB of Figures 7- 9 , two layered structures 20 , 20 ' are integrated which share one transparent conductor layer 92 which is the top transparent conductor layer of the first layered structure 20 and, at the same time , the base transparent conductor layer of the second layered structure 20 ' .

[0092] As said, optionally, the active low-e transparent structure 1A, IB can further comprise , on top of the third transparent conductor layer 92 ' , one or more additional superlattice films 80 , 80 ' stacked on each other and alternated with further transparent conductor layers ( repeating the same pattern of alternating layers ) .

[0093] By increasing the number of layers , it is possible to increase the energy ef ficiency of the low-e transparent structure 1 , 1A, IB . At the same time, by increasing the number of layers , it is possible to vary the transparency ( in particular, reducing the transparency to visible light or to one color ) of the low-e transparent structure . Accordingly, the number of layers (i.e. the number of layered structures 20, 20' stacked on the substrate 70) can be chosen on the basis of the desired effects in terms of efficiency and / or of the required aesthetic design.

[0094] All that has been described regarding the layers 91, 81, 10, 82, 92 of the first layered structure 20 applies also to all the additional layers 91' , 81' , 10' , 82' , 92' of the additional layered structures 20' .

[0095] The orientation of the layers 4A-4L, 2A-2E, 3A-3D of nanocrystals of the additional superlattice structure 10' can be concordant with that of the first superlattice structure 10 (i.e. with the energy gaps decreasing in the same direction) as in Figure 7, or opposite to that of the first superlattice structure 10 (i.e. with the energy gaps decreasing in opposite directions) as in Figure 9.

[0096] In an operative configuration of the active low-e transparent structure 1, 1A, IB the transparent conductor layers 91, 92, 91' are electrically connected to generate a current in a circuit when the active low- e transparent structure 1, 1A, IB is irradiated by the light S.

[0097] In practice, two of the transparent conductor layers 92, 91' can be electrically connected to an anergy storage system or to a load 30 in order to form a photovoltaic device such as the ones illustrated in Figures 1, 3, 6-9.

[0098] In particular, the first 91 and the last 92 transparent conductor layer can be connected so as to connect all the layered structures 20 (i.e. the solar cells formed thereby) in series, as in Figures 7-6. Alternatively, at least three, and preferably all, of the transparent conductor layers 91, 92, 91' can be connected so as to connect the layered structures 20 (i.e. the solar cells formed thereby) in parallel, as in Figures 8-9.

[0099] The active low-e transparent structure so devised is very versatile and can be used for different applications, by choosing a suitable substrate 70. For example, in some embodiments, the transparent substrate 70 is a panel, such as a pane of glass or the like, suitable for closing an opening, such as a window or the like, in a fagade of a building. In one of these embodiments, the low-e transparent structure 1, 1A, IB is a low-e glass pane.

[0100] In other embodiments, the transparent substrate 70 is a foldable or flexible film, such as a film suitable for being fixed on a wall or on any other surface (e.g. a paper-like film) . Optionally, the substrate 70 has sticking properties ( i . e . it comprises an external face , aimed to be fixed on surface , treated to be adhesive or provided with adhesive means , such as any kind of adhesive substance or any other sticking system) . In one of these embodiments the low-e transparent structure 1 , 1A, IB is a wallpaper .

[0101] In an alternative solution, which does not form part of the present invention, the substrate 70 is nontransparent ( so , for example , it is possible to make a low-e structure 1 , 1A, IB that is a non-transparent wallpaper or, more generally, a non-transparent insulation coating) .

[0102] The preferred method of making the active low-e transparent structure 1 , 1A, IB comprises at least the steps of :

[0103] - depositing the first transparent conductor layer 91 on the transparent substrate 70 ;

[0104] - depositing the first dielectric layer 81 on the first transparent conductor layer 91 ; depositing the superlattice structure 10 comprising a plurality of superimposed layers 4A-4L, 2A-2E , 3A-3D of nanocrystals 41-49 , 21-25 , 31-34 on the first dielectric layer 81 ; - depositing the second dielectric layer 82 on the superlattice structure 10; depositing the second transparent conductor layer 92 on the second dielectric layer 82.

[0105] Optionally, after the step of depositing the second transparent conductor layer 92, further steps of deposition are repeated one or more times, in the same order as above, to obtain a repetitive sequence of layers 91, 81, 10, 82, 92 with the same pattern of alternance, as in Figures 7-9.

[0106] Optionally, the layers 4A-4L, 2A-2E, 3A-3D of nanocrystals of the superlattice structures 10, 10' can change for maximal solar efficiency (i.e. the layers of the first superlattice structure 10 are not be the same as those of the second superlattice structure 10' , to account for varying spectral behavior) .

[0107] Preferably, all the layers are deposited directly on each other.

[0108] The operation of the active low-e transparent structure is clear and evident from what has been described above.

[0109] In practice it has been found that the active low- e transparent structure according to the present invention achieves the intended aim and objects, since it has both photovoltaic and low-e properties , despite being formed by a very limited number of layers .

[0110] In addition, the active low-e transparent structure according to the present invention improves ef ficiency with respect to the prior art .

[0111] Another advantage of the active low-e transparent structure , according to the invention, lies in that it is highly versatile .

[0112] A further advantage of the active low-e transparent structure , according to the invention, lies in that it is highly reliable , relatively easy to manufacture and at low costs .

[0113] On top of the above , the active low-e transparent structure , according to the invention, can be incorporated in di f ferent parts of a building ( or of a means of transport , or in of any existing structure ) with very low weight impact on the overall structure and without the need for extra reinforcement .

[0114] Furthermore , the active low-e transparent structure , according to the invention, provides an alternative to known solutions .

[0115] The invention thus devised is susceptible of numerous modi fications and variations , all of which are within the scope of the inventive concept ; all the details may furthermore be replaced with other technically equivalent elements.

[0116] For example, obviously, the low-e transparent structure can be used (in particular incorporated) not only in buildings, but also in any other structure (e.g. civil or industrial constructions, bridges, streets, implants of any kind) or in means of transportation (such as ships, trains, planes, trucks, caravan, etc . ) . In practice, the materials used, as well as the dimensions, may be any according to the requirements and the state of the art.

Claims

C L A I M S1 . An active low-e transparent structure , in particular for building-integrated photovoltaics applications , comprising a transparent substrate on which at least a first layered structure is arranged, said layered structure comprising : a superlattice film consisting of a superlattice structure sandwiched between a first dielectric layer and a second dielectric layer ;- two transparent conductor layers , between which said superlattice film is sandwiched; wherein said superlattice structure comprises a plurality of superimposed layers of nanocrystals and is configured to generate a flow of electrons across said layers when it is irradiated by solar radiation .2 . The active low-e transparent structure according to claim 1 , wherein the first dielectric layer is configured to be an electron transport layer and the second dielectric layer is configured to be an electron blocking layer, or vice versa .3 . The active low-e transparent structure according to claim 1 or 2 , wherein each of said layers of nanocrystals comprises an array of nanocrystals which have a same energy gap, and wherein said layersof nanocrystals are sorted by the energy gap of the nanocrystals in ascending order from said first dielectric layer towards said second dielectric layer, or vice versa .4 . The active low-e transparent structure according to claim 2 and 3 , wherein said layers of nanocrystals are sorted so that a maximum energy gap layer is adj acent to said second dielectric layer which is an electron blocking layer, and a minimum energy gap layer is adj acent to said first dielectric layer which is an electron transport layer .5 . The active low-e transparent structure according to any of the preceding claims , wherein said dielectric layers are made of a metal oxide and / or of a metal alloy .6 . The active low-e transparent structure according to any of the preceding claims , wherein the first dielectric layer is made of a material chosen among TiCh , ZnO, SnCh , and SnO, so as to be an electron transport layer ; and the second dielectric layer is made of NiO or MoOx, so as to be an electron blocking layer ; or vice versa .7 . The active low-e transparent structureaccording to any of the preceding claims , wherein said two transparent conductor layers are configured to be refractive layers and are adapted to be electrically connected so that said layered structure functions as a solar cell .8 . The active low-e transparent structure according to any of the preceding claims , wherein said transparent conductor layers are made of a transparent conductive oxide , such as ITO or FTO, or of Ag, or Au, or Al .9 . The active low-e transparent structure according to any of the preceding claims , wherein said transparent substrate is a panel , such as a glass pane or the like , suitable for closing an opening, such as a window or the like , in a fagade of a building .10 . The active low-e transparent structure according to any of the claims 1 to 8 , wherein said transparent substrate is a foldable or flexible film, optionally with sticking properties , such as a film suitable for being fixed on a wall or on other surfaces .11 . The active low-e transparent structure according to any of the preceding claims , furthercomprising at least a second superlattice film stacked on top of said first layered structure and sandwiched between said first layered structure and a third transparent conductor layer .12 . The active low-e transparent structure according to the preceding claim, further comprising, on top of said third transparent conductor layer, one or more additional superlattice films , stacked on each other and alternated with further transparent conductor layers .13 . A photovoltaic device comprising an active low-e transparent structure according to any of the preceding claims , wherein two of said transparent conductor layers are electrically connected to an energy storage system or a load .14 . Photovoltaic device comprising an active low-e transparent structure according to claim 11 or 12 , wherein at least three of the transparent conductor layers are electrically connected to form a plurality of solar cells connected in parallel .15 . A method of making an active low-e transparent structure , comprising at least the steps of :a ) depositing a first transparent conductor layer on transparent substrate ; b ) depositing a first dielectric layer on said first transparent conductor layer ; c ) depositing a superlattice structure compris ing a plurality of superimposed layers of nanocrystals on said first dielectric layer ; d) depositing a second dielectric layer on said superlattice structure ; e ) depositing a second transparent conductor layer on said second dielectric layer ; wherein said superlattice structure is configured to generate a flow of electrons across said layers when it is irradiated by solar radiation .16 . The method according to the preceding claim, wherein, after said step e ) , further steps of deposition corresponding to said steps b ) to e ) are repeated one or more times in order to obtain a repetitive sequence of layers with the same pattern of alternance .

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