WO2018113983A1

WO2018113983A1 - Optoelectronic device with a 2d-perovskite active layer

Info

Publication number: WO2018113983A1
Application number: PCT/EP2016/082452
Authority: WO
Inventors: Sachin KINGE; Zhenyu Kevin YANG; Sjoerd Hoogland; Edward Sargent
Original assignee: Toyota Motor Europe; The Governing Council Of The University Of Toronto
Priority date: 2016-12-22
Filing date: 2016-12-22
Publication date: 2018-06-28
Also published as: JP2020502769A

Abstract

An optoelectronic device comprising an electron transport layer, an active layer (10), and a hole transport layer is provided. The active layer comprises a layered 2-dimensional perovskite matrix structure (1, 2) and quantum dots (3) included therein.

Description

Optoelectronic device with a 2D-perovskite active laver

FIELD OF THE DISCLOSURE [0001] The present disclosure is related to optoelectronic devices, and more particularly to infrared optoelectronic devices.

BACKGROUND OF THE DISCLOSURE [0002] Optoelectronic devices, also referred to as electroluminescent devices, include diodes, such as light emitting diodes (LEDs) or photodiodes. Such LEDs and photodiodes, in particular infrared LEDs (IR-LEDs) and infrared (IR) - photodiodes, are used in the communication and sensing technology. For example, IR LEDs may be integrated into automobile components for 3D gesture recognition, or communication applications.

[0003] Both LEDs and photodiodes are semiconductor diodes having substantially a similar structure. Therefore in the following, when it is referred to an "LED", this also shall include photodiodes. An LED comprises essentially three layers, i.e. an electron transport layer (ETL) and hole transport layer (HTL), between which an active layer (AL) is sandwiched. The ETL and HTL are also referred to as charge transmission layers (CTL). The active layer is a light emitting layer.

[0004] An important aspect of optoelectronic devices is their efficiency, e.g. the efficiency of a LED to convert electricity to light or of a photodiode to convert light into electricity. The efficiency of a LED can be indicated by its External

Quantum Efficiency (EQE). The EQE of a LED is the ratio of the number of photons emitted from the LED to the number of electrons passing through the device.

There have been different approaches in the prior art to ameliorate the efficiency of optoelectronic devices.

[0005] In particular, colloidal quantum dots (CQDs) are one of the most promising candidates for creating a new generation of optoelectronic devices, in particular LEDs. So far, most of CQD based LEDs comprise a CQD emission (i.e. active) layer sandwiched between two carrier transport layers (i.e. an electron transport layer ETL and a hole transport layer HTL) using different organic or inorganic materials.

[0006] Quantum dots (QDs) are semiconductor nanoparticles (<100nm) and have unique optoelectronic properties, such as size-tunable photoluminescence (PL), narrow emission linewidth, high photoluminescence quantum yield and excellent photostability. They have been widely used as active materials for solar cells, light-emitting diodes (LEDs) and photodetectors.

[0007] Solution processed QD-based light-emitting diodes (LEDs) have shown high efficiency and high brightness with electroluminescence in both the visible and near infrared (NIR) spectroscopic regimes, which is comparable to that capable with polymers, organic molecules and even commercial group III-V LEDs.

[0008] Engineering of charge transport and emissive materials has continually resulted in better charge injection/blocking behavior and radiative recombination within the QD layers, leading to more efficient devices.

[0009] Solution-processed QD-based LEDs, regardless of the emission wavelength, have a common double-heterojunction architecture in which the emissive QD layer is sandwiched between the electron transport layer (ETL) and the hole transport layer (HTL).

[0010] The high efficiency of radiative recombination within QD cores is not only determined by the efficient charge injection and blocking behavior provided by both ETL and HTL, but also depends on the QD photoluminescence quantum efficiency (PLQE). Although NIR QD solutions have luminescence efficiency up to ~40% (depending on the specific wavelength), the PLQEs of corresponding QD films are much lower due to the nonradiative recombination and dissociation of charge carriers at surface defects and material interfaces.

[0011] Several strategies exist to avoid this PL self-quenching effect, such as the preparation of type-I core-shell heterostructures, or encapsulation by inorganic semiconductor or polymer matrix, cf.: [0012] Tessler, N.; Medvedev, V.; Kazes, M.; Kan, S.; Banin, U. Efficient Near- Infrared Polymer Nanocrystal Light-Emitting Diodes. Science 2002, 295, 1506- 1508,

[0013] Steckel, J. S.; Coe-Sullivan, S.; Bulovic, V.; Bawendi, M. G. 1.3 pm to 1.55 μιη Tunable Electroluminescence from PbSe Quantum Dots Embedded within an Organic Device. Adv. Mater. 2003, 15, 1862-1866, and

[0014] Moroz, P.; Liyanage, G.; Kholmicheva, N. N.; Yakunin, S.; Rijal, U.; Uprety, P.; Bastola, E.; Mellott, B.; Subedi, K.; Sun, L.; Kovalenko, M. V.; Zamkov, M. Infrared Emitting PbS Nanocrystal Solids through Matrix Encapsulation. Chem. Mater. 2014, 26, 4256-4264.

[0015] These, however, introduce high charge transport barriers and thus increase the device power consumption. This is because the bandgap of the protection layer (polymer or shelling) is larger than the bandgap of the QD emissive center, which creates the charge transport from CTLs to QDs.

[0016] Recently introduced quantum-dot-in-perovskite (DiP) heterocrystals have been demonstrated to be a promising platform for NIR QD-LEDs, cf.:

[0017] Ning, Z.; Gong, X.; Comin, R.; Walters, G.; Fan, F.; Voznyy, O.; Yassitepe, E.; Buin, A.; Hoogland, S.; Sargent, E. H. Quantum-dot-in-perovskite solids. Nature 2015, 523, 324-328, and

[0018] Gong, X.; Yang, Z.; Walters, G.; Comin, R.; Ning, Z.; Beauregard, E.; Adinolfi, V.; Voznyy, O.; Sargent, E. H. Highly Efficient Quantum Dot Near-Infrared Light-Emitting Diodes. Nature Photonics ^ 2016, 10, 253-257.

[0019] With the long carrier diffusion length provided by the perovskite matrix epitaxially matched to QDs, the DiP thin films show efficient charge transport without compromising QDs' PLQE. The corresponding devices show high radiance and more importantly, a power conversion efficiency of 5.2%, a new record among NIR QD LEDs.

[0020] Metal halide perovskites share a general chemical formula ABX₃, where A is a monovalent cation, B is the divalent metal ion or ion combination, and X is the halide group. Encapsulation of PbS QDs with the 3-D (3-Dimensional) perovskites {methylammonium lead halide (MAPbX₃, X = CI, Br, I)} to enhanced stability against degradation is recently investigated.

[0021] However, these 3D organolead based perovskite matrices, such as methylammonium lead halide (MAPDX3, X = CI, Br, I), suffer from their intrinsically low stability against heating and moisture due to their low formation energy and the vibration of the methylammonium cations. This leads to the gradual decomposition of the perovskite crystals under forward bias and causes the DiP hybrid LEDs to break down at a relatively low voltage of ~4.5 V.

[0022] The 3D perovskite matrix concept is shown in figure 4, in which it is shown that current injection can origin from different directions and the conductivity along x, y, z-axis of the perovskite matrix should be the same. Hence carrier can lose the energy quickly before being extracted for external load.

SUMMARY OF THE DISCLOSURE

[0023] Currently, it remains desirable to provide an optoelectronic device with an enhanced efficiency and stability, in particular against heating and moisture.

[0024] Therefore, according to embodiments of the present disclosure, an optoelectronic device is provided comprising an electron transport layer, an active layer, and a hole transport layer. The active layer comprises a layered 2- dimensional perovskite matrix structure and quantum dots included therein.

[0025] Accordingly, the active layer comprises a 2-D (2-Dimensional) perovskite encapsulating quantum dots. Said perovskite is also a photoactive material, cf.:

[0026] Cao, D. H.; Stoumpos, C. C; Farha, O. K.; Hupp, J. T.; Kanatzidis, M.

G. 2D Homologous Perovskites as Light-Absorbing Materials for Solar Cell

Applications. Journal of the American Chemical Society '2015, 137, 7843-7850.

[0027] In other words, in the active layer a carrier injection matrix is created

(i.e. provided) surrounding the quantum dots that is based on 2D perovskites instead of 3D perovskites. This is because in 2D case, only the vertical direction

(with respect to horizontally arranged electron transport layer and hole transport layer) maintains high conductivity due to specific origination of the layered structure. This can lead to lowered losses and higher carrier extraction efficiency.

[0028] The terms 2D and 3D desirably refer to different perovskite structures, where 3D structures may share a general chemical formula of ABX₃, where A is a monovalent cation, B is the divalent metal ion or ion combination, and X is the halide group. 2D structures according to the disclosure may have the chemical formula of A₂BX₄, where A is a monovalent bulky cation, B is the divalent metal ion or ion combination, X is the halide group.

[0029] The layers of the layered 2-dimensional perovskite matrix structure may be perpendicular or at least substantially perpendicular with regard to the electron transport layer and the hole transport layer.

[0030] The layers of the perovskite matrix structure may be arranged, such that the diffusion of (electronic) carriers between the electron transport layer and the hole transport layer is directionally confined by the layers of the 2-dimensional perovskite matrix structure.

[0031] Accordingly, the layers of the perovskite matrix structure may be vertically arranged with regard to a horizontally arranged electron transport layer and a horizontally arranged hole transport layer, so that the diffusion of carriers (i.e. electrons and/or holes) between the electron transport layer and the hole transport layer is directionally confined to a vertical direction. In other words, the layers of the 2-dimensional perovskite matrix structure hinder the carriers from moving in a horizontal direction, i.e. a direction not parallel to the layers.

[0032] The quantum dots may comprise lead (II) sulfide (PbS).

[0033] Said material PbS is suitable to provide an optoelectronic device which is configured to emit light (such as an IR-LED) in an infrared spectrum. However, also other materials or combinations of materials may be used. For example the quantum dots may comprise materials from IHV, III-V, II-VI or IV-VI type.

[0034] Desirably alkylammonium lead iodide is formed on the quantum dots.

[0035] The layers of the layered 2-dimensional perovskite matrix may comprise structure surface attached insulant organic ligands. [0036] The layers of the layered 2-dimensional perovskite matrix structure may comprise organic cations with alkyl groups.

[0037] The layered 2-dimensional perovskite matrix structure may be of a metal halide perovskite having a chemical formula A2BX4, where A is a monovalent cation, B is a divalent metal ion or ion combination, and X is a halide group.

[0038] The layered 2-dimensional perovskite matrix structure may have layers comprising (BA)₂PbI₄ perovskite. BA may include (or consist of) a C4H₉ H₃ ⁺ cation a butylammonlum cation. Pbl₄ ^2" may be a lead tetraiodide anion.

[0039] The layered 2-dimensional perovskite matrix structure may have layers comprising QHgNhb^"1" alternating with layers comprising Pbl*^2".

[0040] Pbl₄ ^2" layers are desirably part of the 2D perovskite structures.

[0041] The 2D perovskites may be e.g. A₂PbI₄, where A is a monovalent cation.

[0042] Actually the two ions (here: Pbl₄ ^2" and C4H₉NIV) may construct the 2D perovskite crystalline film, where Pbl₄ ^2~ is the anion, and QHglMhb* is the cation.

[0043] The invention also refers to a method for fabricating an optoelectronic device. In the method it is provided a hole transport layer, an active layer, and an electron transport layer. The active layer is formed by encasing quantum dots in a layered 2-dimensional perovskite matrix structure.

[0044] The step of providing the active layer may comprise:

- providing a predetermined material, in particular lead (II) sulfide (PbS), and preparing a quantum dot solution of said material, and

- capping the quantum dots with (BA)₂PbI₄.

[0045] BA may include (or consist of) a C4H₉NH₃ ⁺ cation, a butylammonium cation. Pbl₄ ^2" may be a lead tetraiodide anion.

[0046] The step of providing the active layer may comprise:

- adding a perovskite precursor, in particular Pbl₂ and MAI (Methyl ammonium iodide), into an alkylamine solvent,

- mixing the resulting solution with the quantum dot solution, and

- substituting MA+ cations serving as ligands by the amine molecules such that alkylammonium lead iodide is formed on the quantum dots. [0047] MA⁺ may be the methylammonium cation CH₃NH₃ ⁺.

[0048] It is intended that combinations of the above-described elements and those within the specification may be made, except where otherwise contradictory.

[0049] It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the disclosure, as claimed.

[0050] The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments of the disclosure and together with the description, serve to explain the principles thereof.

BRIEF DESCRIPTION OF THE DRAWINGS

[0051] Fig. 1 shows a schematic representation of the active layer of an exemplary optoelectronic device according to an embodiment of the present disclosure;

[0052] Fig. 2 shows a theoretical model of the active layer of Fig. 1.

[0053] Fig. 3a shows a schematic exemplary optoelectronic device according to an embodiment of the present disclosure;

[0054] Fig. 3b shows the band alignment corresponding to the optoelectronic device of fig. 3a; and

[0055] Fig. 4 shows a schematic representation of an active layer of an optoelectronic device of the prior art. DESCRIPTION OF THE EMBODIMENTS

[0056] Reference will now be made in detail to exemplary embodiments of the disclosure, examples of which are illustrated in the accompanying drawings. Wherever possible, the same reference numbers will be used throughout the drawings to refer to the same or like parts. [0057] Fig. 1 shows a schematic representation of the active layer 10 of an exemplary optoelectronic device according to an embodiment of the present disclosure. The active layer 10 consists of a carrier injection matrix surrounding a plurality of quantum dots 3 (i.e. a dots-in-2D-perovskite active layer 10). The carrier injection matrix is based on 2D perovskites, instead of 3D perovskites as known from the prior art (also cf. fig. 4). This is because in 2D case, as shown in fig. 1, only the vertical direction maintains high conductivity due to specific origination of the layered structure. This can lead to lowered losses and higher carrier extraction efficiency.

[0058] The terms 2D and 3D refer to different perovskite structures, where 3D structures share the general chemical formula of ABX₃, where A is a monovalent cation, B is the divalent metal ion or ion combination, and X is the halide group. 2D structures have the chemical formula of A₂BX_4/ where A is a monovalent bulky cation, B is the divalent metal ion or ion combination, X is the halide group.

[0059] In particular, the carrier injection matrix may comprise Pbl₄ ^2" octahedral layers 1 which are separated from each other by QHgNl layers 2. In other words, the Pbl₄ ^2" octahedral layers 1 are sandwiched by C4H₉NI layers 2.

[0060] Pbl₄ ^2" layers are part of the 2D perovskite structures (the 2D perovskites are A₂PbI₄, where A=monovalent cation). Actually the two ions Pbl₄ ^2" and C₄H₉NIV construct the 2D perovskite crystalline film, where Pbl₄ ^2" is the anion, and the QHgNhb ^" is the cation. Accordingly, the layers shown in fig. 1 are a schematic illustration of the actual active layer.

[0061] In fig. 1 it is schematically shown that there may be horizontal layers, e.g. above and below the quantum dots 3, i.e. there may be layers which are arranged not along the vertical direction. These layers schematically represent ligands, by which the quantum dot surfaces are well-passivated. In the actual active layer, those surface layers would be relatively thin and thus would not affect the charge transfer from perovskite to quantum dot.

[0062] The quantum dots 3 may be colloidal quantum dots. The quantum dots 3 are defined as any semiconductor particle with a band gap of e.g. 4.0- 5.0 eV. However, the bandgap of the quantum dots can be tuned and hence other values may be selected. The quantum dots are made of materials from II-IV, III-V, II-VI or IV-VI type. More preferably the quantum dots comprise lead (II) sulfide (PbS). This material is in particular suitable, if the LED is configured as a IR-LED. The quantum dots 3 may be prepared by wet chemical, synthetic methods or physical, chemical vapor deposition methods.

[0063] In fig. 1 the concept of charge injection within the dots-in-2D- perovskite active layer 10 is also shown. It is noted that only the case of carrier vertical transport through the 2D perovskite matrix is shown in fig. 1. In dots-in- 2D-perovskites, the carrier injection is confined into a pre-defined direction (e.g. in fig. 1, vertical to the substrates). Desirably, said predefined direction is substantially perpendicular with regard to the electron transport layer and the hole transport layer, as e.g. shown in fig. 3A.

[0064] Injected electrons and holes can efficiently meet up in a single dot since the carrier diffusion is directionally confined (i.e. vertically). This confinement is facilitated by the organic separation layer inside the perovskite which forms a moderate barrier for the carriers.

[0065] Fig. 2 shows a theoretical model of the active layer of Fig. 1. The theoretical model of dots-in-2D-perovskite active layer 10 clearly shows the layer- structure of 2D perovskite. In Figure 2, only the quantum dots 3 and Pbl₄ ^2" anions of layers 1 of fig. 1 are shown. The

cations are not shown for clarity reasons.

[0066] The speculated mechanism of the layered structure-guided confined charge diffusion is shown in figure 1. Firstly, the charge diffusion along the vertical direction (i.e., parallel to the Pbl₄ ^2" octahedral layers 1) enhance the vertical injection of carriers from the ETL/HTL layers into the Pbl₂ and then directly to quantum dots. The carriers usually travel in the Pbl₄ ^2" layer (layer 1 in fig. 1) since it is much more conductive than C₄H₉NH₃ ⁺ layer 2. This accelerates the charge recombination in a single quantum dot 3. This is supported by the fact that all tested devices according to the present disclosure have shown low turn-on voltages of 1.1-1.4 eV, close to the intrinsic bandgap of PbS QDs (~1 eV). [0067] On the other hand, the length and steric hindrance of the organic groups (the alkyl chain (C4H9 ) may be regarded as the organic part) can be further tailored to adjust the barrier, so the charge carriers can still easily diffuse along the lateral direction (i.e. the vertical direction in fig. 1). Based on these adjustments, the photoluminescence quantum efficiency of the active material is not affected by exciton migration along the diffusion direction. The turn-on voltage of the device is therefore not significantly increased by the insertion of the insulant organic ligand backbones, so good external quantum efficiency is preserved.

[0068] In the following an exemplary method of providing an active layer (i.e. manufacturing of the active layer) according to the present disclosure is described. PbS QDs emitting at the infrared regime were synthesized following a well- developed hot injection method with some modifications. The oleic acid surface ligands were exchanged with MAPbI₃ perovskite and were further removed by subsequent purification processing. The QDs are PbS QDs, however, the surface is passivated by perovskite ligands (e.g., CH₃NH₃PbI₃ as described here). The MAPbl₃-capped QDs are highly soluble in hydrophilic volatile alkylamine solvents such as butylamine, pentylamine, and hexylamine. The desired amount of perovskite precursors (i.e., Pbl₂ and MAI) were also added into the alkylamine solvent.

[0069] This solution was then mixed with the exchanged QD solution. During the redispersion, MA+ cations serving as ligands were then substituted by the amine molecules such that alkylammonium lead iodide formed on the PbS QDs. The exchanged QDs with the perovskite precursors were finally spin-cast onto glass substrates and annealed at 70°C under inert atmosphere. The resulting active layer comprises PbS QDs 3 and the 2D perovskite (containing Pbl₄ ^2~ anion and C₄H₉NH3⁺), as described above and shown schematically in fig. 1 and 2.

[0070] The presence of 2D perovskite formation may be confirmed by x-ray diffraction (XRD). The orientation of the crystal reflected by XRD may in particular confirm the orientation of the 2D perovskite crystals alignment as the presence of the vertical layers, as shown e.g. in Fig. 1. [0071] Fig. 3a shows an schematic exemplary optoelectronic device (e.g. an LED 100) according to an embodiment of the present disclosure.

[0072] The LED 100 comprises an electron transport layer (ETL) 12, an active layer 10 and a hole transport layer (HTL) 14. The active layer is arranged between the electron transport layer (ETL) 12 and the hole transport layer (HTL) 14. The HTL 14 may comprise or may consist of F8 (PFO Polyfluorene). The ETL 12 may comprise or may consist of T1O2 (Titanium dioxide). The exemplary LED may further comprise first and second electrodes 15, 16 and a substrate (not shown). The first electrode 15 may be operated as the cathode. The second electrode 16 may be operated as the anode. The first electrode may comprise an indium tin oxide (ΓΤΟ) layer. Furthermore the second electrode may comprise a silver (Ag) layer and M0O3 (Molybdenum trioxide) layer. Ag is desirably on top of the M0O3 layer, as shown in fig. 3a. The substrate may be a glass substrate. The first or second electrode may be coated on the substrate.

[0073] Fig. 3b shows the band alignment corresponding to the optoelectronic device of fig. 3a. In particular, fig. 3b shows the energy level diagram of the optoelectronic device according to the disclosure, i.e. it shows the energy level below vacuum in eV of the single layers of the LED 100. The second electrode 16, which is used as an anode, has preferably a level of -5.7 eV. The hole transport layer has preferably an energy level ranging from -5.8 eV to -2.9 eV. The active layer 10 has preferably an energy level ranging from -5.0 eV to -4.0 eV. Alternatively, the active layer may have energy bandgap from 1.7 to 3.5 eV or from -3.3 to -5.7 eV, which is the bandgap regime that is available for this specific architecture of the LED. The electron transport layer has preferably an energy level ranging from -7.2 eV to -4.0 eV. The first electrode 15, which is used as a cathode, has preferably a level of -4.8 eV.

[0074] Fig. 3B also indicates the materials of the active layer, i.e. means PbS quantum dots and the surrounding 2D perovskite. Said perovskite may have the chemical formula (BA)₂PbI₄. BA may comprise C4H₉NH3⁺ cation and butylammonium cation. Pbl₄ ^2" may be lead tetraiodide anion. [0075] As a comparative example, fig. 4 shows a schematic representation of an active layer of an exemplary optoelectronic device of the prior art. In particular, fig. 4 schematically shows the concept of charge injection within dot-in-3D- perovskite active layer 10' from a perovskite matrix to PbS CQD 3'. In the 3D perovskite matrix concept current injection can be from different directions and the conductivity along x, y, z-axis of perovskite matrix should be the same. Hence carrier can lose the energy quickly before being extracted for external load. The 3D perovskite matrix may consist of metal halide perovskite crystals ABX₃, where A is a monovalent cation, B is a divalent metal cation, and X is a halide anion. The further material shown in fig. 4 and used in the 3D perovskite is MA⁺. MA⁺ may be the methylammonium cation CH₃NH₃ ⁺.

[0076] Throughout the disclosure, including the claims, the term "comprising a" should be understood as being synonymous with "comprising at least one" unless otherwise stated. In addition, any range set forth in the description, including the claims should be understood as including its end value(s) unless otherwise stated. Specific values for described elements should be understood to be within accepted manufacturing or industry tolerances known to one of skill in the art, and any use of the terms "substantially" and/or "approximately" and/or "generally" should be understood to mean falling within such accepted tolerances.

[0077] Where any standards of national, international, or other standards body are referenced (e.g., ISO, etc.), such references are intended to refer to the standard as defined by the national or international standards body as of the priority date of the present specification. Any subsequent substantive changes to such standards are not intended to modify the scope and/or definitions of the present disclosure and/or claims.

[0078] Although the present disclosure herein has been described with reference to particular embodiments, it is to be understood that these embodiments are merely illustrative of the principles and applications of the present disclosure. [0079] It is intended that the specification and examples be considered as exemplary only, with a true scope of the disclosure being indicated by the following claims.

Claims

1. An optoelectronic device comprising:

an electron transport layer,

an active layer, and

a hole transport layer, wherein

the active layer comprises a layered 2-dimensional perovskite matrix structure and quantum dots included therein.

2. The optoelectronic device according to claim 1, wherein the layers of the layered 2-dimensional perovskite matrix structure are perpendicular or at least substantially perpendicular with regard to the electron transport layer and the hole transport layer.

3. The optoelectronic device according to claim 1 or 2, wherein the layers of the perovskite matrix structure are arranged such that the diffusion of carriers between the electron transport layer and the hole transport layer is directionally confined by the layers of the 2-dimensional perovskite matrix structure.

4. The optoelectronic device according to any one of the preceding claims, wherein

the quantum dots comprise lead (II) sulfide (PbS).

5. The optoelectronic device according to any one of the preceding claims, wherein

alkylammonium lead iodide is formed on the quantum dots.

6. The optoelectronic device according to any one of the preceding claims, wherein

the layers of the layered 2-dimensional perovskite matrix structure comprise organic cations with alkyl groups.

7. The optoelectronic device according to any one of the preceding claims, wherein

the layered 2-dimensional perovskite matrix structure is of a metal halide perovskite having a chemical formula A2BX4, where A is a monovalent cation, B is a divalent metal ion or ion combination, and X is a halide group.

8. The optoelectronic device according to any one of the preceding claims, wherein

the layered 2-dimensional perovskite matrix structure comprises (BA)₂PbI₄ perovskite, wherein BA includes 0₄Η₉ΝΗ₃ ⁺ cation as butylammonium cation, and wherein Pbl₄ ^2~ is lead tetraiodide anion.

9. The optoelectronic device according to any one of the preceding claims, wherein

the layered 2-dimensional perovskite matrix structure has layers comprising QHgN alternating with layers comprising Pbl₄ ^2~.

10. Method of fabricating an optoelectronic device, comprising the steps of:

providing a hole transport layer,

providing an active layer, and

providing an electron transport layer, wherein

the active layer is formed by encasing quantum dots in a layered 2- dimensional perovskite matrix structure.

11. Method according to claim 10, wherein

the step of providing the active layer comprises:

providing a predetermined material, in particular lead (II) sulfide (PbS), and preparing a quantum dot solution of said material, and

capping the quantum dots with (BA)₂PbI₄, wherein BA includes 0,Η₉ΝΗ₃ ⁺ cation and butylammonium cation, and wherein Pbl₄ ^2" is lead tetraiodide anion.

12. Method according to any one of claims 10-11, wherein the step of providing the active layer comprises:

adding a perovskite precursor, in particular Pbl₂ and MAI, into an alkylamine solvent,

mixing the resulting solution with the quantum dot solution, and substituting MA+ cations serving as ligands by the amine molecules such that alkylammonium lead iodide is formed on the quantum dots.