Improved superlattice film

Abstract

A superlattice film including a superlattice structure disposed between a first conductor and a second conductor and including a plurality of stacked layers of nanocrystals, each of the layers including an array of nanocrystals having the same energy gap, and the layers being sorted in ascending order from the first conductor to the second conductor by the energy gap of the nanocrystals such that the layer with the maximum energy gap is adjacent to the first conductor and the layer with the minimum energy gap is adjacent to the second conductor, the superlattice film further including at least one of an electron blocking layer interposed between the layer with the maximum energy gap and the first conductor and an electron transport layer interposed between the layer with the minimum energy gap and the second conductor.

Description

Technical Field

[0001] The present invention relates to a superlattice film for a photovoltaic device such as a thin-film solar cell, and a modular device including a plurality of superlattice films, although not particularly limited thereto.

Background Art

[0002] As is known, a solar cell or a photovoltaic cell is a device that directly converts the energy of light into electricity by the photovoltaic effect.

[0003] The most relevant characteristic of a solar cell is its efficiency. The first generation of solar cells (also called conventional, traditional, or wafer-based cells) is usually made of crystalline silicon, and more precisely includes materials such as polysilicon and single-crystalline silicon. Individual traditional solar cells are generally combined to form a module, also known as a solar panel.

[0004] Subsequently, the second generation of solar cells, generally known as thin-film solar cells, was developed. Known thin-film solar cells are usually produced by depositing one or more thin layers or thin films (TF: thin film) of a photovoltaic material on a substrate such as glass, plastic, or metal. The thin films usually include materials such as cadmium telluride (CdTe), copper indium gallium diselenide (CIGS), and amorphous thin-film silicon (a-Si, TF-Si).

[0005] Thin-film solar cells have a thickness variation from several nanometers (nm) to several tens of micrometers (μm), and are much thinner than conventional silicon-based solar cells. As a result, thin-film solar cells can be more flexible, lighter, and thus more versatile than crystalline silicon solar cells. Furthermore, these known thin-film solar cells are less expensive than conventional crystalline silicon solar cells.

[0006] For example, today, thin-film solar cells are commonly used as a semi-transparent photovoltaic glazing material that can be integrated into a building's integrated photovoltaic power generation system and laminated onto windows.

[0007] However, in the state of the art, thin-film solar cells are less efficient than conventional crystalline silicon solar cells.

[0008] In fact, known thin-film solar cells have a maximum efficiency of about 10%. In recent years, new materials that can be used as absorption photovoltaic materials for thin-film solar cells have been studied, including superlattices.

[0009] As is known, the superlattices referred to include a periodic structure containing an array of nanocrystals, which are semiconductor particles on the order of a few nanometers in size and are also known as "quantum dots" or "quantum wires". More precisely, such nanocrystals have a size smaller than the Bohr radius of the material from which they are made, and as a result, they have unique optical and electronic properties due to quantum effects.

[0010] Typically, photovoltaic superlattices are isotropic structures and the nanocrystals are actually shuffled.

[0011] Although theoretically very promising, these photovoltaic superlattices developed so far have not reached an efficiency sufficient to be useful for commercial applications.

[0012] In fact, currently used thin-film solar cells having a superlattice as an absorption photovoltaic material have an efficiency of about 8% - 12%.

[0013] International Publication No. WO 2021 / 070169 discloses an improved superlattice structure for thin-film solar cells, which includes a plurality of stacked layers of nanocrystals and is configured to generate an electron flow across the layers when irradiated with radiation. Each of the layers includes an array of nanocrystals having substantially the same size and shape, and the nanocrystals of each of the layers have a different size and / or a different shape from the nanocrystals of the other layers. In practice, in International Publication No. WO 2021 / 070169, the layers are sorted in an order such that the lattice structure is anisotropic along the cross direction where superconductivity is required. As an effect of this feature, in the superlattice structure of International Publication No. WO 2021 / 070169, there is a preferred direction (i.e., the cross direction) in which electrons e- flow.

[0014] The superlattice structure disclosed by International Publication No. WO 2021 / 070169 substantially improves the efficiency of thin-film solar cells, but further improvements are still possible and desirable, particularly from the viewpoints of efficiency and versatility.

Summary of the Invention

Problems to be Solved by the Invention

[0015] The object of the present invention is to solve the above technical problems, remove the drawbacks of the background art and overcome the limitations, and provide a superlattice film having improved efficiency over the prior art.

[0016] Within the scope of this object, the object of the present invention is to provide a superlattice film that is easy to manufacture and competitive in terms of cost.

[0017] Furthermore, the object of the present invention is to provide a highly versatile superlattice film. Another object of the present invention is also to provide an alternative to known solutions.

Means for Solving the Problems

[0018] This object, as well as these and other objects which will become more apparent hereinafter, is a superlattice film including a superlattice structure disposed between a first conductor and a second conductor and including a plurality of stacked layers of nanocrystals, each of the layers including an array of nanocrystals having the same energy gap, and the layers being sorted in ascending order from the first conductor to the second conductor by the energy gaps of the nanocrystals such that the layer having the maximum energy gap is adjacent to the first conductor and the layer having the minimum energy gap is adjacent to the second conductor, the superlattice film further including - an electron blocking layer interposed between the layer having the maximum energy gap and the first conductor, and - an electron transport layer interposed between the layer having the minimum energy gap and the second conductor is achieved by a superlattice film further including at least one of them.

[0019] This object and these objects are also achieved by the modular device according to claim 11.

[0020] The foregoing features and advantages of the present invention, as well as further features and advantages, will become more apparent from the following description of preferred but non-exclusive embodiments of a superlattice film according to the present invention and a modular device including the superlattice film shown as a non-limiting example in the accompanying drawings.

Brief Description of the Drawings

[0021]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Best Mode for Carrying Out the Invention

[0022] Note that the above drawings are not drawn to an exact scale in order to better show the underlying structure of the present invention and must be regarded as schematic diagrams unless otherwise indicated.

[0023] Detailed Description of the Invention Referring to the drawings cited, the superlattice film, generally designated by reference numeral 1, includes a superlattice structure 10 disposed between a first conductor 91 and a second conductor 92 (i.e., a conductive element).

[0024] The conductors 91 and 92 are preferably conductive layers. The superlattice structures 10, 100 include a plurality of stacked layers 4A - 4L (or 2A - 2E and 3A - 3D in FIG. 3) of nanocrystals 41 - 50 (or 21 - 25 and 31 - 34 in FIG. 3).

[0025] Each of the layers 4A - 4L, 2A - 2E, 3A - 3D includes an array of nanocrystals 41 - 50, 21 - 25, 31 - 34 having the same energy gap (as is known, the energy gap in a nanocrystal is the difference in energy between the bottom of the conduction band of an electron and the top of the valence band).

[0026] In fact, all of the nanocrystals in the same layers 4A - 4L, 2A - 2E, 3A - 3D have the same size and shape in order to have the same energy gap. It is useful to clarify that the term "shape" in this specification and the appended claims refers to the mere geometric shape (i.e., geometric structure) of the nanocrystal regardless of its size.

[0027] In the superlattice structures 10, 100, the layers 2A - 2L, 3A - 3L, 4A - 4L are sorted in ascending order from the first conductor 91 towards the second conductor 92 according to the energy gaps of the nanocrystals 41 - 50, 21 - 25, 31 - 34. In other words, the layers 2A - 2L, 3A - 3L, 4A - 4L are sorted in such an order that the energy gaps of the nanocrystals 41 - 50, 21 - 25, 31 - 34 decrease from the first conductor 91 towards the second conductor 92.

[0028] Generally, all the layers 4A - 4L, 2A - 2E, 3A - 3E are sorted in ascending order from the first conductor 91 towards the second conductor 92 (along the cross - direction Y where conductivity is required) according to the sizes of the nanocrystals 21 - 25, 31 - 34.

[0029] In fact, the energy gap within a nanocrystal is inversely proportional to the size of the nanocrystal. Therefore, as can be seen in Figure 1, the maximum energy - gap layers 4L, 2E (i.e., the layers containing the nanocrystals 50 with the maximum energy gap) are adjacent to the first conductor 91, and the minimum energy - gap layers 4A, 2A (i.e., the layers containing the nanocrystals with the minimum energy gap) are adjacent to the second conductor 92.

[0030] In this way, in the superlattice structures 10, 100, electrons e− are induced to flow along the cross - direction Y from the maximum energy - gap layer 4L towards the minimum energy - gap layer 4L, and the reverse does not occur.

[0031] In Figures 1 and 2, the nanocrystals are depicted as spherical only for the sake of simplification to show any possible shape, and the nanocrystals 41 - 50 can have any suitable shape such as a hexahedron, pentahedron, octahedron, cuboctahedron, hexagonal crystal, etc.

[0032] In a preferred embodiment, all the nanocrystals 41 - 50 in the same layers 4A - 4L have the same size, and thus, each of the layers 4A - 4L differs from the other layers only in the size of the nanocrystals 41 - 50.

[0033] However, in some alternative embodiments, as depicted in FIG. 3, the superlattice structure 100 includes a first type of layers 2A-2E including nanocrystals having a first shape, and a second type of layers 3A-3D including nanocrystals having a second shape different from the first shape, where the first type of layers 2A-2E are alternating with the second type of layers 3A-3D.

[0034] Regarding the composition of the nanocrystals 21-25, 31-34, these are made from semiconductor materials such as CdS, CdSe, CdTe, InP, InAs, ZnS, ZnSe, HgTe, GaN, GaP, GaAs, GaSb, InSb, Si, Ge, AlAs, AlSb, PbSe, PbS, PbTe, InGaAs, InGaN, AlInGaP.

[0035] In a preferred embodiment, the nanocrystals 21-25, 31-34 are made from one or more of the following materials: PbSe, PbS, PbTe, CdS, CdSe, CdTe.

[0036] Preferably, all of the nanocrystals 21-25, 31-34 are made from the same material. In practice, the superlattice structures 10, 100 can be any of the superlattice structures described in International Publication No. WO 2021 / 070169.

[0037] Advantageously, the nanocrystals 41-50 are fixed at predetermined positions within the layers 4A-4L so as to have both an energy and a mechanical orientation.

[0038] In particular, it should be noted that within the superlattice structures 10, 100, the nanocrystals are fixed at predetermined positions so that they have an energy orientation. In practice, the energy gap of the nanocrystals is such that the electrons e - are aligned so as to be able to cross the entire superlattice structures 10, 100.

[0039] Note that within the superlattice structures 10, 100, the nanocrystals 41-50, 21-25, 31-34 are fixed at predetermined positions so as to have an orientation in the shape direction.

[0040] More specifically, the shape and orientation of the nanocrystals 41-50, 21-25, 31-34 are provided such that the nanocrystals have not only an energy orientation but also a mechanical orientation.

[0041] Finally, in a preferred embodiment, the nanocrystals 41-50, 21-25, 31-34 are fixed at predetermined positions within the layers 4A-4L, 2A-2E, 3A-3E so as to have both an energy and a mechanical orientation.

[0042] Advantageously, the gaps and connections between the nanocrystals 21-25, 31-34 are controlled by ligand molecules connected to the nanocrystals 21-25, 31-34.

[0043] As a result of such a synergistic combination of energy and mechanical orientation, within the superlattice structures 10, 100, as a result of photon absorption, the probability that the electrons e- excited within the nanocrystals 41-50, 21-25, 31-34 "jump" (move) in the cross direction Y towards the second conductor contact 92 to the adjacent nanocrystals 41-50, 21-25, 31-34 is very high, and the probability that such electrons "jump" (move) to other adjacent nanocrystals 41-50, 21-25, 31-34 in other directions is very low.

[0044] According to the present invention, the superlattice film 1 is - an electron blocking layer (EBL: electron blocking layer), also called a hole transport layer (HTL), 81 interposed between the maximum energy gap layer 4L and the first conductor 91, and -An electron transport layer (ETL: electron transport layer) 82 (also referred to as a hole blocking layer (HBL)) interposed between the minimum energy gap layer 4A and the second conductor 92, and further includes at least one of them.

[0045] Preferably, as in the illustrated embodiment, the superlattice film 1 includes both the electron transport layer 82 and the electron blocking layer 81.

[0046] As is known, the electron transport layer 82 has physical properties (e.g., charge mobility, energy level orientation, defect state, morphology, and related interface characteristics) useful for the extraction and transport of excited electron carriers, and functions as a hole blocking layer by suppressing charge recombination.

[0047] For example, the electron transport layer 82 can be made of one of the following materials: SnO2, CdSe, WO3, ZnSnO4, ZnO, Pbl2, TiO2, SrTiO3, CH3NH3Bbl3, ZnO2, SnO.

[0048] As is known, the electron blocking layer 81 has an effect substantially opposite to that of the electron transport layer, and reduces the leakage of electrons to the first conductor 91.

[0049] For example, the electron blocking layer 81 can be made of one of the following materials: Spiro-OMeTAD, PEDOT:PSS, PTAA (poly[bis(4-phenyl)(2,4,6-trimethylphenyl)amine]), P3HT, DM, TAT-tBuSty, X26, X36, FDT, SCZF-5, TTE, PTEG, cuprous oxide (Cu2O), copper oxide (CuO), copper(I) thiocyanate (CuSCN), copper(I) iodide (CuI), nickel oxide (NiO x ), MoS2, WS2, SANs, Cu(Tu)I, MnS, CuS, copper indium gallium disulfide (CIGS: copper indium gallium disulfide) nanocrystals, for example, Cu(In 0.75Ga 0.25 )S2 and Cu(In 0.5 Ga 0.5 )S 2。

[0050] The presence of the electron transport layer 82 and / or the electron blocking layer 81 extends the work function between the conductors 91, 92 and the nanocrystals, and thus increases the efficiency of the superlattice film 1, especially when used as a photovoltaic device.

[0051] To enable absorption by the superlattice structure 10, at least one of the conductors (i.e., the first conductor 91) is at least partially transparent to light, preferably transparent to visible light, and even more preferably completely transparent to light.

[0052] FIG. 4 shows the superlattice film 1 used as a photovoltaic device (as a solar cell), and the first conductor 91 and the second conductor 92 of the ninth are connected via an electrical circuit such that electrons e - flow from the first conductor 91 to the second conductor 92 along the intersection direction Y (thus, the current c flows in the opposite direction in the circuit).

[0053] As described above, two or more superlattice films 10 can be combined to form a modular device 110 as depicted in FIG. 5.

[0054] More specifically, the modular device 110 includes at least two superlattice films 1, 1', i.e., the first superlattice film 1 and the second superlattice film 1', laminated to each other along the intersection direction Y such that the minimum energy gap layer 4A of the first superlattice film 1 faces the minimum energy gap layer 4A' of the second superlattice film 1'.

[0055] The conductive layer 92 is interposed between the minimum energy gap layer 4A of the first superlattice film 1 and the minimum energy gap layer 4A' of the second superlattice film 1', and as a result, this single conductive layer 92 constitutes the second conductor 92 of both the first superlattice film 1 and the second superlattice film 1.

[0056] In addition to the first superlattice film 1 and the second superlattice film 1', the modular device 110 can include at least a third superlattice film (not shown) laminated on the second superlattice film 1' such that the maximum energy gap layer of the additional superlattice film laminated in the same manner, for example, the third superlattice film, faces the maximum energy gap layer 4L' of the second superlattice film 1'. In this case, a single conductive layer constitutes the first conductors 91' of both the second superlattice film and the third superlattice film.

[0057] The fourth superlattice film can be laminated on the third superlattice film such that the minimum energy gap layer of the fourth superlattice film faces the minimum energy gap layer of the third superlattice film 1', and so on.

[0058] In other words, the modular device 110 includes a series of superlattice structures 10, 100 alternating with conductive layers 91, 92.

[0059] In the operating configuration of the modular device 110, the conductors 911, 92, 91' are electrically connected so as to generate an electric current in the circuit when the modular device 110 is irradiated with light.

[0060] It should be noted that inside the superlattice structure 10, a gradient for generating a "superconductor" in the conduction direction (cross direction Y) is provided. Thus, the superlattice film 1 (and the modular device 110) can be used for any application that requires such behavior (for example, for manufacturing a supercapacitor).

[0061] According to an alternative and simpler solution, a single superlattice structure 10 can be used for applications that require "superconductor" behavior such as a supercapacitor.

[0062] The operation of the superlattice film is clear and evident from the above. In fact, the superlattice film according to the present invention has been found to be able to improve efficiency over the prior art and achieve the intended goals and purposes.

[0063] Another advantage of the superlattice film according to the present invention is that it can provide a highly versatile thin-film solar cell.

[0064] A further advantage of the superlattice film according to the present invention is that it is highly reliable, relatively easy to manufacture, and competitive in terms of cost.

[0065] Furthermore, the superlattice film according to the present invention provides an alternative to known solutions. The present invention thus conceived is capable of numerous modifications and variations, all of which are within the scope of the concept of the present invention, and all details may be further replaced by other technically equivalent elements.

[0066] In fact, the materials and dimensions used may be arbitrary according to requirements and the state of the art.

[0067] Therefore, the scope of the present invention is indicated by the appended claims rather than the above description, and it is intended that all modifications within the meaning and scope of the equivalents of the claims be included.

Claims

1. A superlattice film comprising a superlattice structure including a plurality of superimposed layers of nanocrystals, disposed between a first conductor and a second conductor, Each of the layers comprises an array of nanocrystals having the same energy gap, and the layers are sorted in ascending order from the first conductor to the second conductor by the energy gap of the nanocrystals, such that the layer with the largest energy gap is adjacent to the first conductor and the layer with the smallest energy gap is adjacent to the second conductor. The superlattice film is - An electron blocking layer interposed between the maximum energy gap layer and the first conductor, - An electron transport layer interposed between the minimum energy gap layer and the second conductor A superlattice film further comprising at least one of the following.

2. The superlattice film according to claim 1, comprising both the electron transport layer and the electron blocking layer.

3. The electron transport layer is made of the following material: SnO、SnO ２ 、CdSe、WO ３ 、ZnSnO ４ 、ZnO、ZnO2、Pbl ２ 、TiO ２ 、SrTiO ３ 、CH ３ NH ３ BbI ３ A superlattice film according to claim 1, made from one of the following.

4. The aforementioned electron blocking layer is made of the following materials: Spiro-OMeTAD, PEDOT: PSS, PTAA, P3HT, DM, TAT-tBuSty, FDT, SCZF-5, TTE, PTEG, Cu ２ O, CuO, CuSCN, CuI, NiO x MoS ２ , WS ２ The superlattice film according to claim 1, made from one of SANs, Cu(Tu)I, MnS, CuS, or CIGS nanocrystals.

5. The superlattice film according to claim 1, wherein the first conductor is at least partially transparent to light, and preferably transparent to visible light.

6. The superlattice film according to claim 1, wherein the layers are sorted in ascending order from the first conductor to the second conductor according to the size of the nanocrystals.

7. The aforementioned layer, - A first type of layer containing nanocrystals having a first shape, - A second type of layer comprising nanocrystals having a second shape different from the first shape described above. The first type of layer is alternated with the second type of layer, The superlattice film according to claim 1.

8. The superlattice film according to claim 1, wherein the nanocrystals are fixed at predetermined positions within the layer such that they have both energetic and mechanical orientations.

9. The aforementioned nanocrystals are made of the following materials: CdS, CdSe, CdTe, InP, InAs, ZnS, ZnSe, HgTe, GaN, GaP, GaAs, GaSb, InSb, Si, Ge, AlAs, AlSb, PbSe, PbS, PbTe, InGaAs, InGaN, AlInGaP A superlattice film according to claim 1, made from one or more of the following.

10. The superlattice film according to claim 1, wherein the nanocrystals are made from one or more of the following materials: PbSe, PbS, PbTe, CdS, CdSe, and CdTe.

11. A modular apparatus comprising at least two superlattice films according to any one of claims 1 to 10, namely a first superlattice film and a second superlattice film, wherein the first superlattice film and the second superlattice film are laminated such that the minimum energy gap layer of the first superlattice film faces the minimum energy gap layer of the second superlattice film. A modular apparatus in which a single conductive layer constitutes the second conductor in both the first and second superlattice films.

12. The modular apparatus according to claim 11, further comprising at least a third superlattice film, the third superlattice film being laminated on the second superlattice film such that the maximum energy gap layer of the third superlattice film faces the maximum energy gap layer of the second superlattice film, wherein a single conductive layer constitutes the first conductor of both the second and third superlattice films.

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