IMPROVED SUPERLATTICE FILM

Abstract

A superlattice film includes a superlattice structure that is arranged between a first conductor and a second conductor and includes a plurality of superimposed layers of nanocrystals; wherein each of the layers has an array of nanocrystals which have a same energy gap, and wherein the layers are sorted by the energy gap of the nanocrystals in ascending order from the first conductor towards the second conductor, so that a maximum energy gap layer is adjacent to the first conductor and a minimum energy gap layer is adjacent to the second conductor. The superlattice film further includes at least one among an electron blocking layer interposed between the maximum energy gap layer and the first conductor, and an electron transport layer interposed between the minimum energy gap layer and the second conductor.

Claims

1. A superlattice film comprising a superlattice structure that is arranged between a first conductor and a second conductor and comprises a plurality of superimposed layers of nanocrystals; wherein each of said layers comprises an array of nanocrystals which have a same energy gap, and wherein said layers are sorted by the energy gap of the nanocrystals in ascending order from said first conductor towards said second conductor, so that a maximum energy gap layer is adjacent to said first conductor and a minimum energy gap layer is adjacent to said second conductor; said superlattice film further comprising at least one among: an electron blocking layer interposed between the maximum energy gap layer and the first conductor, and an electron transport layer interposed between the minimum energy gap layer and the second conductor.

2. The superlattice film according to claim 1, which comprises both said electron transport layer and said electron blocking layer.

3. The superlattice film according to claim 1, wherein the electron transport layer is made of one of the following materials: SnO, SnO.sub.2, CdSe, WO.sub.3, ZnSnO.sub.4, ZnO, ZnO.sub.2 Pbl.sub.2, TiO.sub.2, SrTiO.sub.3, and CH.sub.3NH.sub.3Bbl.sub.3.

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

5. The superlattice film according to claim 1, where said first conductor is at least partially transparent to the light.

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

7. The superlattice film according to claim 1, wherein said layers comprise: layers of a first type which comprise nanocrystals having a first shape, and layers of a second type which comprise nanocrystals having a second shape that is different from said first shape; said layers of the first type being alternated with said layers of the second type.

8. The superlattice film according to claim 1, wherein said nanocrystals are fixed in predetermined positions within said layers such that they have both an energetic and a mechanical alignment.

9. The superlattice film according to claim 1, wherein said nanocrystal are made of one or more 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, and AlInGaP.

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

11. A modular device comprising at least two superlattice films according to claim 1, a first superlattice film and a second superlattice film, which are stacked so that the minimum energy gap layer of the first superlattice film faces the minimum energy gap layer of the second superlattice film; wherein a single conductor layer constitutes the second conductor of both said first and second superlattice film.

12. The modular device according to claim 11, further comprising at least a third superlattice film that is stacked on said second superlattice film so 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 said second and third superlattice films.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0028] The foregoing, as well as further characteristics and advantages of the present disclosure, will become better apparent from the following description of a preferred, but not exclusive, embodiment of a superlattice film, according to the disclosure, and of a modular device comprising the superlattice film illustrated by way of nonlimiting example in the accompanying drawings, wherein:

[0029] FIG. 1 is a schematic representation of a superlattice film, according to the disclosure;

[0030] FIG. 2 is a schematic representation of a superlattice structure included in the superlattice film, according to the disclosure;

[0031] FIG. 3 is a schematic representation of an alternative superlattice structure;

[0032] FIG. 4 is a schematic representation of a superlattice film, according to the disclosure, in use in a photovoltaic device; and

[0033] FIG. 5 is a schematic representation of a modular device comprising two superlattice films, according to the disclosure.

[0034] It should be noted that the above-mentioned drawings must be intended as schematic, since they do not reflect the exact proportions, in order to better show the underlying structure of the disclosure.

DETAILED DESCRIPTION OF THE DRAWINGS

[0035] With reference to the cited figures, the superlattice film, generally designated by the reference numeral 1, comprises a superlattice structure 10 that is arranged between a first conductor 91 and a second conductor 92 (i.e. electrically conductive elements).

[0036] The conductors 91, 92 are preferably conductive layers.

[0037] The superlattice structure 10, 100 comprises a plurality of superimposed 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).

[0038] Each of the layers 4A-4L; 2A-2E; 3A-3D comprises an array of nanocrystals 41-50, 21-25, 31-34 which have the same energy gap (as known, the energy gap in a nanocrystal is the difference of energy between the bottom of the conduction band and the top of the valence band of the electrons). 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.

[0039] In the superlattice structure 10, 100, 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 conductor 91 towards the second conductor 92. 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 decreases from the first conductor 91 to the second conductor 92.

[0040] In general, then, all the layers 4A-4L; 2A-2E, 3A-3E are sorted by the size of the nanocrystals 21-25, 31-34 in ascending order (along the cross direction Y along which the electrical conductivity is required) from the first conductor 91 to the second conductor 92.

[0041] In fact, the energy gap in a nanocrystal is inversely proportional to the size of the nanocrystal.

[0042] It follows that, as can been seen in FIG. 1, a maximum energy gap layer 4L, 2E (i.e. the layer that comprises the nanocrystals 50 having the maximum energy gap) is adjacent to the first conductor 91 and a minimum energy gap layer 4A; 2A (i.e. the layer that comprises the nanocrystal having the minimum energy gap) is adjacent to the second conductor 92.

[0043] In this manner, in the superlattice structure 10, 100, the 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 not vice versa

[0044] In FIGS. 1, and 2 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.

[0045] In the preferred embodiments, all the nanocrystals 41-50 of the same layer 4A-4L have the same size, and thus each layer 4A-4L differs from the others only for the size of the nanocrystals 41-50.

[0046] However, in some alternative embodiments, as the one depicted in FIG. 3, the superlattice structure 100 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 2A-2E type are alternated with the layers of the second type 3A-3D.

[0047] 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, PbTe, InGaAs, InGaN, AlInGaP.

[0048] 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.

[0049] Preferably, all the nanocrystals 21-25, 31-34 are made of the same material.

[0050] In practice, the superlattice structure 10, 100 can be any superlattice structure described in WO 2021/070169.

[0051] 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.

[0052] In particular, it should be noted that within the superlattice structure 10, 100 the nanocrystals are fixed in predetermined positions in such a way that they have energetic alignment. In practice, the energy gaps of the nanocrystals are aligned so as to allow the electrons e.sup. (excited by radiation S absorption) to transverse the whole superlattice structure 10, 100.

[0053] It also should be noted then that, within the superlattice structure 10, 100 the nanocrystals 41-50 21-25, 31-34 are fixed in predetermined positions in such a way that they have a shape directional alignment.

[0054] 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.

[0055] 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.

[0056] Advantageously, the gaps and connections between the nanocrystals 21-25, 31-34 is controlled by the Ligand molecules that are connected to the nanocrystals 21-25, 31-34.

[0057] As a result of the synergistic combination of such energetic and mechanical alignment, within the superlattice structure 10, 100 there is a very high probability that an electron e excited in a nanocrystals 41-50 21-25, 31-34 as a result of the absorption of a photon jumps (moves) to the nanocrystal 41-50 21-25, 31-34 that is adjacent in the cross direction Y towards the second conductor contact 92 and there is a very low probability that such electron e jumps (moves) to the other nanocrystals 41-50, 21-25, 31-34 which are adjacent in the other directions.

[0058] According to the disclosure, the superlattice film 1 further comprises at least one among: [0059] an electron blocking layer (EBL) 81 (also called hole transport layer (HTL)) that is interposed between the maximum energy gap layer 4L and the first conductor 91, and [0060] an electron transport layer (ETL) 82 (also called hole blocking layer (HBL)) that is interposed between the minimum energy gap layer 4A and the second conductor 92.

[0061] Preferably, as in the illustrated embodiment, the superlattice film 1 comprises both said electron transport layer 82 and said electron blocking layer 81.

[0062] As known, an electron transport layer 82 is 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 serves as a hole-blocking layer by suppressing charge recombination.

[0063] For example, the electron transport layer 82 can be made of one of the following materials: SnO.sub.2, CdSe, WO.sub.3, ZnSnO.sub.4, ZnO, Pbl.sub.2, TiO.sub.2, SrTiO.sub.3, CH.sub.3NH.sub.3Bbl.sub.3, ZnO.sub.2, Sno.

[0064] As known, an electron blocking layer 81 has substantially the opposite effect of the electron transport layer and it reduces the leakage of electrons toward the first conductor 91.

[0065] 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 (Cu.sub.2O), cupric oxide (CuO), Copper(I) thiocyanate (CuSCN), Copper(I) iodide (CuI), Nickel oxide (NiO.sub.x), MOS.sub.2, WS.sub.2, SANS, Cu(Tu)I, MnS, CuS, copper indium gallium disulfide (CIGS) nanocrystals such as Cu(In.sub.0.75Ga.sub.0.25)S.sub.2 and Cu(In.sub.0.5Ga.sub.0.5)S.sub.2.

[0066] The presence of the electron transport layer 82 and/or electron blocking layer 81 extends the work function between the conductor 91, 92 and the nanocrystals and thus increases the efficiency of the superlattice film 1, in particular when used as a photovoltaic device.

[0067] In order to allow the absorption by the superlattice structure 10, at least one conductor (namely the first conductor 91) is at least partially transparent to the light, preferably transparent to the visible light, even more preferably completely transparent to the light.

[0068] FIG. 4 shows the superlattice film 1 in use as photovoltaic device (as a solar cell): the first conductor 91 and the second 9 conductor 92 are connected via an electric circuit so that, in consequence of the solar radiation S, the electrons e-flow along the cross direction Y from the first conductor 91 to the second conductor 92 (and consequently a current c flows in the circuit in the opposite direction).

[0069] Two or more superlattice films 10, as described above, can be combined to form a modular device 110, such as the one depicted in FIG. 5.

[0070] In greater details, the modular device 110 comprises at least two superlattice films 1, 1, a first superlattice film 1 and a second superlattice film 1, which are stacked on top of each other, along the cross direction Y, so 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.

[0071] A 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, so that this single conductive layer 92 constitutes the second conductor 92 of both said first 1 and second 1 superlattice film 1.

[0072] In addition to the first 1 and the second 1 superlattice film the modular device 110 can comprise further superlattice films stacked in the same manner: for example at least a third superlattice film (not illustrated) that is stacked on the second superlattice film 1 so that the maximum energy gap layer of 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 conductor 91 of both said second 1 and third superlattice films.

[0073] A fourth superlattice film can be stacked on the third superlattice film so 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.

[0074] In other words, the modular device 110 comprises a series of superlattice structures 10, 100 alternated with conductive layers 91, 92.

[0075] In an operative configuration of the modular device 110 the conductors 911, 92, 91 are electrically connected to generate a current in a circuit when the modular device 110 is irradiated by the light.

[0076] It should be noted that inside the superlattice structure 10 it is provided a gradient that produces a super conductor in the electrical conductivity direction (the cross direction Y) and thus the superlattice film 1 (as well as the modular device 110) is usable for any application that requires such a behavior (e.g. for making supercapacitors).

[0077] According to an alternative and simpler solution, the sole superlattice structure 10 can be used for applications which require a super conductor behavior, such as supercapacitors.

[0078] The operation of the superlattice film is clear and evident from what has been described above.

[0079] In practice it has been found that the superlattice film according to the present disclosure achieves the intended aim and advantages, since it allows to improve the efficiency with respect to prior art.

[0080] Another advantage of the superlattice film, according to the disclosure, resides in that it allows to provide a thin film solar cell that is highly versatile.

[0081] A further advantage of the superlattice film, according to the disclosure, resides in that it is highly reliable, relatively easy to manufacture and at competitive costs.

[0082] Furthermore, the superlattice film, according to the disclosure, provides an alternative to known solutions.

[0083] The disclosure thus devised is susceptible of numerous modifications 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.

[0084] In practice, the materials used, as well as the dimensions, may be any according to the requirements and the state of the art.

[0085] Scope of the disclosure is thus indicated by the appended claims, rather than the foregoing description, and all changes that come within the meaning and range of equivalence of the claims are therefore intended to be embraced therein.