WO2016124555A1

WO2016124555A1 - Light-emitting electrochemical cell based on perovskite nanoparticles or quantum dots

Info

Publication number: WO2016124555A1
Application number: PCT/EP2016/052103
Authority: WO
Inventors: Meltem J. AYGÜLER; Ruben D. COSTA; Pablo Docampo; Michael D. Weber
Original assignee: Ludwig-Maximilians-Universität München; Friedrich-Alexander Universität Erlangen-Nürnberg
Priority date: 2015-02-02
Filing date: 2016-02-02
Publication date: 2016-08-11

Abstract

The present invention relates to the field of light-emitting electrochemical cells. In particular, the present invention relates to a light-emitting electrochemical cell based on perovskite nanoparticles or quantum dots in combination with an ionic liquid or a mixture of an ionically conducting material and an inorganic salt. Moreover, the present invention relates to methods of manufacturing such a light-emitting electrochemical cell and to uses of such a light- emitting electrochemical cell.

Description

Light-emitting Electrochemical Cell

Based On Perovskite Nanoparticles or Quantum Dots

FIELD OF THE INVENTION

BACKGROUND OF THE INVENTION

In the last decades, Organic Light-Emitting Diodes (OLEDs) have been extensively investigated as the potential next generation technology for flat panel display and lighting (see Figure 1 A). The interest in this technology has been triggered by reports on significant breakthroughs in device efficiency, lifetime and achievable colors, including white.

However, multilayer devices are needed to obtain high performance levels. Such a multilayer architecture is obtained by sequential deposition of different layers by means of physical or chemical vapor evaporation under high-vacuum conditions, spin-coating, and doctor-blading techniques. The multilayer architecture strongly hampers the device fabrication on any kind of substrates, which is one of the most appealing aims to ensure a wide market application. Additionally, these devices use air-sensitive electrodes or charge injection layers that require a rigorous encapsulation to prevent their degradation. As such, the fabrication has to be carried out in an inert environment or vacuum. Nowadays, the successful entry of OLEDs into the general lighting market requires apart from high performance levels a strong reduction in the production cost of the devices. In this respect, it is of particular importance to be able to generate electroluminescence from devices that feature i) simple architectures based on air-stable charge injection interfaces, ii) a fabrication process under air conditions on any kind of substrates, and iii) high performance levels in terms of stability, efficiency, and brightness.

To this end, the use of mobile ions is emerging as a powerful strategy to tackle the aforementioned points. This new type of electroluminescence device, referred to as Light- Emitting Electrochemical Cells (LECs), are the leading example (see Figure 1 B) (Pei et al., 1995; Pei et al., 1996; Costa et al., 2012; Meier et al., 2014).

An LEC is a single layer device that is processed from solution under air conditions and that does not rely on air-sensitive charge-injection layers or metals for electron injection. Furthermore, working examples of LECs prepared on any kind of 3D substrates have been recently demonstrated. This greatly simplifies their preparation and passivation/stability against ambient conditions and makes them more cost efficient.

In its simplest form, it consists of at least one active layer containing either a mixture of a light-emitting polymer, an ion conducting polymer, and an inorganic salt or only one ionic transition-metal complex (iTMC) based on either Cu(I), Ru(II), Os(II), Ir(III) metal ions (Pei et al., 1995; Pei et al., 1996; Costa et al., 2012; Meier et al, 2014). These devices are interesting candidates for use in thin-film lighting applications as they operate at very low voltages, yielding high power efficient devices, and are easy to produce under ambient conditions on any kind of substrate.

As stated above, the majority of the electroluminescent materials applied in LECs are polymers and iTMCs. Examples of LECs based on other luminescent materials like, for example, quantum dots (QDs) are scarce, while nanoparticles (NPs) have not been used up to date. So far, there are only four examples of QD-LECs.

In 2011, Leger and colleagues reported on yellow and orange LECs by using an active layer, in which CdSe/ZnS QDs are blended with a PF/PPV copolymer - poly[(9,9-dioctyl-2,7- divinylene-fluorenylene)-alt-co-{2-meth-oxy-5-(2-ethyl-hexyloxy)-l,4-phenylene}], and the polymerizable ionic liquid allyltrioctylammonium allylsulfonate (ATOAAS) as the source of counterions (Bader et al., 2011). They used an unusual driving mode that consists of a pre- charging of the device at 8 V until a steady current is achieved followed by a driving at 16 V for ~1 min. After the pre-charging, the luminance-current- voltage (LIV) features were recorded. The devices showed turn-on voltages of around 7V with maximum luminance values of 200-300 cd/m at 16 V. However, the stability of such devices is poor. Recently, Watkins and colleagues reported on blue, green, red, and white, solid-state and flexible QD- LECs by using the same approach as the Leger group (Qian et al., 2014). They used a polyvinylcarbazole (PVK) and the ionic liquid l-butyl-3-methylimidazolium hexafluorophosphate (BMIM-PF₆) as main components in the active layer. Brightness ranges from 20 to 1000 cd/m² depending on the color, while efficiencies of around 0.5-1.5 cd/A were noted for all of the devices. Finally, CN 201180036719 discloses the incorporation of quantum dots into LEDs, while CN 103026525 describes the use of QDs-LECs for the treatment and/or prophylaxis and/or diagnosis of diseases and/or cosmetic conditions. However, all QDs-LECs of the prior art are based on combining CdSe/ZnS QDs in a host polymer featuring moderate performance levels in terms of luminance and stability, but rather poor stability values. Additionally, the developed QDs all exhibit significant sub-bandgap defects, which effectively limit the device performance achievable. For instance, trap-assisted recombination can occur, whereby the electron and hole in the exciton relaxes to a trap state, and two carriers subsequently recombine without emission of a photon since QDs have surface state defects. This results in a decrease in the photoluminescence quantum yield (PLQY) of the emitter. Moreover, a significant reduction in PLQY is also observed after ligand-exchange, which is a necessary step for their application in devices.

In 2009, Yueqing et al. reported on the use of metallic NPs to enhance the electroluminescence response of polymer-based LECs (Yueqing et al., 2009). In detail, the presence of Al NPs in the active layer reduces the overall series resistance and enhances the light-emitting area. However, the Al NPs were not implemented as dopant emitters. In 2010, Itoh fabricated ionic based lighting devices using a quasi-solid-state active layer based on a ruthenium complex as the emitter, an ionic liquid as the electrolyte, and metal oxide NPs like Ti0₂, ZnO, Zr0₂ as gelation fillers. No electroluminescence emission from the NPs was reported (Itoh, 2010).

From what is known to the present inventors, the use of metal-halide based perovskite NPs or QDs as emitting materials applied in LECs has not been explored yet.

SUMMARY OF THE INVENTION

As described above, all the aforementioned approaches and devices have significant drawbacks with regard to their function or preparation. Thus, there is a need in the art for improved light-emitting electrochemical cells, in particular for light-emitting electrochemical cells that overcome the above-described drawbacks. In particular, there is a need in the art for light-emitting electrochemical cells that have a higher efficiency, in particular a higher photoluminescence quantum yield and/or a higher power conversion efficiency, and/or do not show a reduction in quantum yield after ligand exchange and/or show electroluminescence at a wider range of wavelengths and/or show quantum confinement effects and/or allow for better tunability of the light emission and/or show stable performances after long storage under ambient conditions like at room temperature or under moist conditions and/or can be prepared at lower cost and/or show no significant sub-band gap states on the surface and/or at the grain boundaries of the nanoparticles which would cause a reduction in PLQY.

It is the object of the present invention to meet such needs.

These objects are solved by the below-described aspects of the present invention, in particular by a light-emitting electrochemical cell according to claim 1 , by a method of manufacturing such a light-emitting electrochemical cell according to claim 12 and by the use of such a light- emitting electrochemical cell according to claim 13. Preferable embodiments are defined in the dependent claims.

Before the present invention is described in more detail below, it is to be understood that the terminology used herein is for the purpose of describing particular embodiments only, and is not intended to limit the scope of the present invention which will be limited only by the appended claims. Unless defined otherwise, all technical and scientific terms used herein have the same meanings as commonly understood by one of ordinary skill in the art. For the purpose of the present invention, all references cited herein are incorporated by reference in their entireties.

Moreover, the following embodiments can, wherever this does not lead to logical contradictions, be combined with each other without restrictions. Hence, the present disclosure encompasses, even where not explicitly spelled out in the following, any feasible combination of the embodiments described below. Furthermore, the present disclosure encompasses, wherever this does not lead to logical contradictions, the combination of any of the embodiments relating to one aspect of the present invention with the other aspects of the present invention described herein.

In a first aspect, the present invention relates to a light-emitting electrochemical cell comprising

- a first electrode,

- a second electrode, and

- a light-emitting layer, wherein said light-emitting layer comprises

(i) nanoparticles or quantum dots comprising or consisting of a perovskite,

and

(ii) an electrolyte which comprises or consists of an ionic liquid or a mixture of an ionically conducting material and an inorganic salt.

As the skilled person will appreciate, in a light-emitting electrochemical cell as defined above, charge injection, charge transport and light emission occur in said light-emitting layer.

Moreover, as the skilled person will appreciate, in a light-emitting electrochemical cell as defined above, said light-emitting layer comprises mobile ions.

Typically, the nanoparticles or quantum dots will consist entirely of said perovskite. Alternatively, the nanoparticles or quantum dots may each consist of a core made of a perovskite surrounded by a shell made from a different material (such as of a different perovskite). As a further alternative, the nanoparticles or quantum dots may consist of a 2D hybrid of a perovskite with an organic material, in which metal-halide octahedra layers and organic layers are arranged in an alternating manner (i.e. the 2D system has a repeating structure in which one or several metal-halide layers are sandwiched between organic layers, thus forming a lamella structure). Additionally, the nanoparticles or quantum dots may consist of a 2D/3D hybrid of a perovskite with an organic material, in which perovskite layers and organic layers are arranged in an alternating manner.

Said perovskite may be a metal halide-based perovskite, which, preferably, is a perovskite composed of

- monovalent organic cations and/or alkali cations,

- divalent metal cations, and

- halide anions.

A light-emitting electrochemical cell according to the first aspect of the present invention comprises a first electrode as anode, a second electrode as cathode, and an additional luminescent layer.

To generate a light-emitting electrochemical cell according to the present invention a perovskite NPs-electrolyte matrix solution may be deposited onto a substrate via any solution- compatible process (e.g. by spray coating), producing a film that shows photoluminescence under excitation above the bandgap energy. The configuration of the double-layer LEC used in the present invention may be: Substrate/ITO/PEDOT:PSS/light-emitting layer/ Aluminum. The anode may be made of ITO or another TCO (transparent conducting oxide) and the cathode may be made of Al or another metal electrode. A PEDOT:PSS layer may be added to flatten the spikes present in the ITO, hence to improve the reproducibility. The light-emitting layer is sandwiched between the bottom anode and the top cathode electrodes.

As it is explained below, the anode and the cathode are preferably facing each other, and the luminescent layer (i.e. light-emitting layer) is interposed in between. However, in alternative embodiments the luminescent layer is not interposed between the anode and the cathode, but it is placed just in juxtaposition.

Preferably, the first electrode (anode) is a transparent electrode placed on a glass substrate made of a material such as indium-tin oxide (ITO), although other electrodes based on silver nanowires and nanocarbon derivatives deposited on glass or flexible substrates are also possible. The substrate may be effectively non-flexible, e.g. a glass or a glass-like material. The substrate may comprise a metal foil, such as steel, Ti, Al, Inconel alloy, or Kovar. Flexible substrates may be also considered. For example, substrates based on polymeric materials, such as poly(ethylene terephthalate), poly(ethylene naphthalate), poly(imide), poly(carbonate), or combinations or derivatives thereof. The substrate may comprise paper or paper-like material.

As anode, a standard ITO-coated glass plate (15 Ω/sq.) may be used, and patterning may be achieved by conventional photolithography. In the experiments described below, such a standard ITO-coated glass plate (15 Ω/sq.), obtained from Naranjo Substrates, (www.naranjosubstrates.com), was used, patterned using conventional photolithography. The substrates were extensively cleaned using sonification in subsequent water-soap, water, and 2- propanol baths. After drying, the substrates were placed in a UV-ozone cleaner (Jetlight 42- 220) for 10 minutes. It should be noted that normal devices are sandwiched, i.e. the active layer is placed in between a first and a second electrode (the anode and the cathode). In such architecture at least one of the electrodes should be at least semitransparent, in order to allow the light to leave the device. ITO may be used as transparent conducting material. However, as an alternative to the use of transparent electrode material, alternative structures may be used, e.g. interdigitated electrodes, and in these alternative structures the electrodes do not need to be transparent, since the active layer is simply put on top of the anode and/or the cathode, and therefore the light is directly allowed to leave the device. The luminescent layer comprises a mixture of the perovskite NPs or quantum dots, and either an ionic liquid (i.e. a salt that has a melting point below 100 °C) or a mixture of an ionically conducting material (in particular an ionically conducting polymer) and an inorganic salt. Optimally, the mixture of an ion-dissolving material and an inorganic salt should have i) wide electrochemical window, ii) high ion mobility, iii) good miscibility with the emitter to avoid phase separations during film forming. The ratio between the components and the perovskite NPs were fixed to the optimum to provide a width of the undoped region which effectively eliminates detrimental interactions between the excited perovskite NPs and the neighboring p- and n-doped regions stabilized by the accumulations of mobile anions.

The perovskite nanoparticles or perovskite quantum dots comprised in said light-emitting layer may be of single or multiple compositions and/or single or multiple sizes.

The light-emitting layer may typically have a thickness of between 10 nm and 10 μιη, such as about 100 nm.

The perovskite nanoparticles may for example have a diameter of up to 1 micron, preferably less than 20 nm to take advantage of the quantum confinement effects. Quantum confinement effects of lead-based semiconductors typically appear for NPs below 20 nm.

The perovskite quantum dots may for example have a diameter of between 10 nm and 20 nm.

The nanoparticles comprising or consisting of a perovskite, quantum dots comprising or consisting of a perovskite, the light-emitting layer and the light-emitting electrochemical cell according to the present invention may be prepared as described in the Examples section below.

Said perovskite may have an AMX₃ stoichiometry, wherein A is an organic cation or alkali metal, M is a metal and X is a halide.

A is an organic cation, e.g.:

A can be a primary, secondary or tertiary ammonium ion, where the substituents may be aryl or alkyl groups or chain.

- A can also be of the form [R¹R²N=CH-NR³R⁴]⁺ _b where each of R¹, R², R³, and R⁴ can be a hydrogen, an alkyl or aryl group/chain:

- A can also be of the form [(R¹R²N)(R³R⁴N)C=NR⁵R⁶]⁺, wherein R¹, R², R³, R⁴, R⁵ and R⁶ can be a hydrogen, an alkyl or aryl group/chain:

For example, A may be guanidinium, as in the experiments described below.

A can also be a monovalent alkali metal ion, such as Cs⁺ or Rb⁺. M is any divalent metal ion such as Sn²⁺, Pb²⁺ or Ge²⁺. X is a halide such as Cl^~, Br^~, Γ or F^_.

The perovskite structure may also be of the form A_1-XB_XMX₃, wherein A and B are any two different cations described above and wherein x is from 0 to 1.

The perovskite structure may also be of the form AMX_3-ZY_Z, wherein X and Y are different halides as described above and wherein z is from 0 to 3. The perovskite structure may also be of the form AM_1-yN_yX₃, wherein M and N are different divalent metal ions as described above and wherein y is from 0 to 1.

The perovskite structure may be a combination of all the above: A_1-xB_xMi_-yN_yX_3-zY_z, wherein A and B are any two different cations described above, wherein x is from 0 to 1, wherein X and Y are different halides as described above, wherein z is from 0 to 3, wherein M and N are different divalent metal ions as described above and wherein y is from 0 to 1.

The electrolyte allows for electrochemical doping of the perovskite material.

The electrolyte may comprise a substantially liquid electrolyte.

The salt may comprise at least one metal salt, comprising a cation, such as Li⁺, Na⁺, K⁺, Rb⁺, Mg⁺, or Ag⁺, and a molecular anion, such as [CF₃S0₃]^~, [C10₄]^_, [(CFSS0₂)₂N]^_, [PF₆]^~ [PF₃(C₂F₅)₃r, [PF₃(CF₃)₃r, [BF₄r, [BF₂(CF₃)₂]-, [BF₂(C₂F₅)₂]^_, [BF₃(CF₃)f, [BF₃(C₂F₅)]^", [B(COOCOO)₂]-, [BOB]^", [CF3SO3]^", [TfJ- [C₄F₉S0₃]^_, [Nff, [(CF₃S0₂)₂N]^{^} ₃ [TFSIf, [(C₂F₅S0₂)₂N]^", [BETI]-, [(CF₃S0₂)(C₄F₉S0₂)Nr, [(CN)₂Nf, [DCAf, [(CF₃S0₂)₃C]- and

The ionically conducting polymer material may be selected from a group consisting of poly(ethylene oxide), poly(propylene oxide), methoxyethoxy-ethoxy substituted polyphosphazane, and poly-ether based poly-urethane, or combinations thereof.

The electrolyte may comprise a gel electrolyte. In the alternative, or as a complement, the electrolyte may comprise a substantially solid electrolyte.

As a complement and/or alternative, an ionically conducting material may comprise at least one non-polymer ionically conducting material, such as a crown ether. The active material may comprise a surfactant, or a polymeric not ionically conducting material, such as polystyrene, poly(methylacrylate), etc.

In this invention, the electrolyte may comprise LiCF₃S0₃ and trimethylolpropane ethoxylate (TMPE) with the mass ratio of 0.3/1.

As alternative and/or complement, the luminescent layer may also comprise a mixture of perovskite NPs with a salt having a melting point below 100 °C, i.e. with an ionic liquid. This salt may also serve for the purpose of electrolyte of the LEC. As such, the electrolyte may comprise at least one ionic liquid. Ionic liquids that may be used are those comprising a positively charged nitrogen atom undergoing four covalent bonds in their molecular structure, such as Ν,Ν,Ν-trimethylbutyl ammonium ion, N-ethyl-N,N-dimethylpropyl ammonium ion, N-ethyl-N,N-dimethylbutyl ammonium ion, N,N-dimethyl-N-propylbutyl ammonium ion, N- (2-methoxyethyl)-N,N-dimethylethyl ammonium ion, l-ethyl-3 -methyl imidazolium ion, 1- ethyl-2,3 -dimethyl imidazolium ion, l-ethyl-3, 4-dimethyl imidazolium ion, l-ethyl-2,3,4- trimethyl imidazolium ion, l-ethyl-2,3,5-trimethyl imidazolium ion, l-butyl-3- methylimidazolium, N-methyl-N-propyl pyrrolidinium ion, N-butyl-N-methyl-pyrrolidinium ion, N-sec-butyl-N-methylpyrrolidinium ion, N-(2-methoxyethyl)-N-methylpyrrolidinium ion, N-(2-ethoxyethyl)-N-methylpyrrolidinium ion, N-methyl-N-propylpiperidinium ion, N- butyl-N-methyl piperidinium ion, N-sec-butyl-N-methylpiperidinium ion, N-(2- methoxyethyl)-N-methyl piperidinium ion and N-(2-ethoxyethyl)-N-methyl piperidinium ion or those comprising a phosphonium-based cation, such as a tetrabutylphosphonium ion (e.g. in tetrabutylphosphonium methanesulfonate) or a tributylmethylphosphonium ion (e.g. in tributylmethylphosphonium methyl sulfate), or those comprising a sulfonium-based cation, such as a trialkylsulfonium ion or a tris(4-tert-butylphenyl)sulfonium ion. The l-butyl-3- methylimidazolium ion is the most preferred cation. On the other hand, as the anion, it is possible to use, for example, the following anions: [PF₆]^~, [PF₃(C₂F₅)₃]^_, [PF₃(CF₃)₃]^~, [BF₄]^~ [BF₂(CF₃)₂r, [BF₂(C₂F₅)₂]^", [BF₃(CF₃)]^", [BF₃(C₂F₅)r, [B(COOCOO)₂]^", [BOBf, [CF₃S0₃]-, [TfJ^", [C₄F₉S0₃r, [Nff, [(CF₃S0₂)₂N]-, [TFSI]^", [(C₂F₅S0₂)₂N]-, [BETI]^~, [(CF₃S0₂)(C₄F₉S0₂)N]^{^}, [(CN)₂N]^~, [DCAf, [(CF₃S0₂)₃C]^" and [(CN)₃C]^"

Finally, the cathode involves air-stable metals like Au, Ag, Al, etc., as well as silver nanowire and nanocarbon based electrodes. Another layer deposited in between the anode and the active layer can be optionally included between the anode and the luminescent layer, such as a Poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS) layer to improve the reproducibility. The device may further comprise a spacer, arranged to maintain a predetermined distance between the electrodes. When using a liquid or semisolid (gel) electrolyte, spacers may, depending on the design of the device, be used to keep the electrodes at a desired distance from each other, and to avoid short circuiting of the device. The electrolyte may comprise a salt. One or both electrodes may be directly or indirectly deposited on the substrate. One or both of the first and second electrodes may be conducting and transparent or semi-transparent. As alternative and/or complement, one or both of the first and second electrodes is coated with a thin layer of a conducting polymer, such as PEDOT:PSS. One or both of the first and second electrodes may comprise a metal. The metal may comprise an air-stable metal, such as Al, Ag, or Au. Alternatively, an air-unstable metal like Ba or Ca and/or a mixture like LiF/Al in combination with a standard encapsulation system can be used.

Regarding film formation, the active layer can be deposited on any of the above-mentioned substrates by any solution-based coating or printing method, such as spin-coating, doctor blade coating, spray-coating, inkjet printing, flexographic printing, screen printing, gravure printing, etc. In these invention examples, active layers featuring different thicknesses ranging were prepared by using doctor-blading and spray-pyrolysis techniques.

The weight ratio between the different components of the light-emitting electrochemical cell may be selected to allow injection at low voltages and currents, ensuring the formation of a doped region at the respective electrode interface, which allows for injection and transport of electronic charge carriers, and the undoped region, separating the doped regions, where charge recombination takes place, resulting in light emission Concerning the driving mode, there is provided a method for generating light, comprising a light-emitting electrochemical cell as described above, and a power source, connected to the first and second electrodes. A power source may be any means suitable for generating a power that can be used with the device. The power source may be arranged to provide a nominal drive voltage of around 2-19 V. The power source may apply nominal drive voltage in both constant and pulsed (100-2000 Hz at triangle, sinus, square forms) schemes. The power source may be arranged to provide a nominal drive current of around 1-100 mA. The power source may apply current in both constant and pulsed (100-2000 Hz at triangle, sinus, square forms) schemes.

Preferably, said light-emitting electrochemical cell generates light by electroluminescence. Preferably, said light-emitting layer generates light by electroluminescence.

As the skilled person will appreciate, said light-emitting electrochemical cell is not an Organic Light-Emitting Diode (OLED).

As the skilled person will appreciate, in a light-emitting electrochemical cell, charge injection, charge transport and light emission occur within the same layer (namely in the light-emitting layer). Thus, charge injection, charge transport and light emission are not spatially separated in different layers (or sublayers) and do not occur in a different layer (or sublayers), and there is no blocking material or charge injection material that would exist spatially separated from the light-emitting material. Preferably, charge injection, charge transport and light emission occur in said light-emitting layer. Preferably, said light-emitting layer comprises mobile ions.

In some embodiments, said nanoparticles or quantum dots consist of a perovskite.

In some embodiments, said nanoparticles or quantum dots consist of a core consisting of a perovskite, preferably a perovskite as defined below, and a shell made from a different material around said core, wherein, preferably, said shell is made of a different perovskite, preferably a perovskite as defined below. Preferably, said nanoparticles or quantum dots consist of a core consisting of a perovskite, preferably a perovskite as defined below, and a shell made from a 2D/3D hybrid of a perovskite with an organic material, wherein the perovskite that is part of said 2D/3D hybrid of a perovskite with an organic material is the same perovskite as the one which said core consists of. In some embodiments, said nanoparticles or quantum dots consist of layers of a perovskite sandwiched between organic layers (i.e. the nanoparticles or quantum dots consist of a 3D or 2D hybrid of a perovskite with an organic material).

In some embodiment, said perovskite is a metal halide-based perovskite.

Preferably, said metal halide-based perovskite is a perovskite composed of

- monovalent organic cations and/or alkali cations,

- divalent metal cations, and

- halide anions.

In some embodiments, said perovskite is an organo-metal halide perovskite.

In some embodiment, light emission of said light-emitting layer is caused by the metal-halide octahedra of said perovskite, wherein, preferably, said metal-halide octahedra mediate both exciton formation and charge recombination. In some embodiments, said organic cations function as spacers for said metal-halide octahedra and, preferably, do not act as chromophores.

In some embodiments, said perovskite has the stoichiometry

A1.i iM1.jNjX3.kYk , wherein

A and B are different monovalent cations, preferably independently selected from the group consisting of

(i) a primary ammonium cation [F^NR¹]^-1-, wherein R¹ is selected from the group consisting of a C1-C20 alkyl group and an aryl group,

(ii) a secondary ammonium cation [H₂NR¹R²]⁺, wherein R¹ and R² are the same or different and are each independently selected from the group consisting of a C₁-C₂₀ alkyl group and an aryl group,

(iii) a tertiary ammonium cation [HNR R R ] , wherein R , R and R are the same or different and are each independently selected from the group consisting of a C₁-C₂o alkyl group and an aryl group,

(iv) a cation having the structure represented by Formula (I) Formula (I),

wherein R¹, R², R³ and R⁴ are the same or different and are each independently selected from the group consisting of a hydrogen atom, a Q- C₂₀ alkyl group and an aryl group,

(v) a cation having the structure represented by Formula (II)

Formula (II),

wherein R¹, R², R³, R⁴, R⁵ and R⁶ are the same or different and are each independently selected from the group consisting of a hydrogen atom, a Q- C₂o alkyl group and an aryl group, wherein, preferably, said cation is guanidinium, and

(vi) an alkali metal cation, more preferably Cs or Rb ;

JVI and N are different divalent metal cations, preferably independently selected from the group consisting of Ge²⁺, Sn²⁺ and Pb²⁺; and

X and Y are different halide anions, preferably independently selected from the group consisting of CI-, Br^~, Γ and F^~;

wherein i is from 0 to 1, wherein, preferably, i is 0;

wherein j is from 0 to 1, wherein, preferably, j is 0; and

wherein k is from 0 to 3, wherein, preferably, k is 0.

some embodiments,

(a) said perovskite has the stoichiometry A_1-;B MX, wherein

(i) a primary ammonium cation [H₃NR¹]^"1", wherein R¹ is selected from the group consisting of a Ci-C₂₀ alkyl group and an aryl group,

(ii) a secondary ammonium cation [H^SHE^R²]^-1", wherein R¹ and R² are the same or different and are each independently selected from the group consisting of a Ci-C2₀ alkyl group and an aryl group,

(iii) a tertiary ammonium cation [HNR^IR²R³]⁺, wherein R¹, R² and R³ are the same or different and are each independently selected from the group consisting of a C₁-C₂₀ alkyl group and an aryl group, a cation having the structure represented by Formula (I)

Formula (I),

wherein R¹, R², R³ and R⁴ are the same or different and are each independently selected from the group consisting of a hydrogen atom, a C1-C20 alkyl group and an aryl group,

(v) a cation having the structure represented by Formula (II)

Formula (II),

wherein R¹, R², R³, R⁴, R⁵ and R⁶ are the same or different and are each independently selected from the group consisting of a hydrogen atom, a C₁-C₂₀ alkyl group and an aryl group, wherein, preferably, said cation is guanidinium, and

(vi) an alkali metal cation, more preferably Cs⁺ or Rb⁺;

M is a divalent metal cation, preferably selected from the group consisting of

Ge²⁺, Sn²⁺ and Pb²⁺; and

X is a halide anion, preferably selected from the group consisting of Cl^~, Br^", Γ and F^~;

wherein i is from 0 to 1, wherein, preferably, i is 0; or said perovskite has the stoichiometry ΑΜ^Ν,-Χ, wherein

A is a monovalent cation, preferably selected from the group consisting of

a primary ammonium cation [H₃NR ] , wherein R is selected from the group consisting of a Q-C20 alkyl group and an aryl group,

a secondary ammonium cation [¾ΝΊ ^ ]⁺, wherein R¹ and R² are the same or different and are each independently selected from the group consisting of a Ci- ^o alkyl group and an aryl group, 1 2 3 1 2 3 (iii) a tertiary ammonium cation [HNR R R ] , wherein R , R and R are the same or different and are each independently selected from the group consisting of a C₁-C₂₀ alkyl group and an aryl group, (iv) a cation having the structure represented by Formula (I)

H

R¹ N ^N'^R4 Formula (I),

R² R³ wherein R¹, R², R³ and R⁴ are the same or different and are each independently selected from the group consisting of a hydrogen atom, a C₁-C₂₀ alkyl group and an aryl group,

(v) a cation having the structure represented by Formula (II)

Formula (II),

wherein R¹, R², R³, R⁴, R⁵ and R⁶ are the same or different and are each independently selected from the group consisting of a hydrogen atom, a Ci-C2o alkyl group and an aryl group, wherein, preferably, said cation is guanidinium, and

(vi) an alkali metal cation, more preferably Cs⁺ or Rb⁺;

M and N are different divalent metal cations, preferably independently selected from the group consisting of Ge²⁺, Sn ⁺ and Pb²⁺; and

X is a halide anion, preferably selected from the group consisting of CF, Br^~, Γ and F^~;

wherein j is from 0 to 1, wherein, preferably, j is 0; or said perovskite has the stoichiometry AM ₃.¾ , wherein

A is a monovalent cation, preferably selected from the group consisting of

(i) a primary ammonium cation [H^NR¹]^"^ wherein R¹ is selected from the group consisting of a C₁-C₂o alkyl group and an aryl group, ι a secondary ammonium cation [H₂NR¹R²]⁺, wherein R¹ and R² are the same or different and are each independently selected from the group consisting of a C₁-C₂₀ alkyl group and an aryl group,

) a tertiary ammonium cation [HNR 1 R2 R 3 ]"!" , wherein R 1 , R2 and R 3 are the same or different and are each independently selected from the group consisting of a alkyl group and an aryl group,

) a cation having the structure represented by Formula (I)

Formula (I),

wherein R¹, R², R³ and R⁴ are the same or different and are each independently selected from the group consisting of a hydrogen atom, a

Ci-C₂o alkyl group and an aryl group,

a cation having the structure represented by Formula (II)

Formula (II),

wherein R¹, R², R³, R⁴, R⁵ and R⁶ are the same or different and are each independently selected from the group consisting of a hydrogen atom, a Q-C20 alkyl group and an aryl group, wherein, preferably, said cation is guanidinium, and

(vi) an alkali metal cation, more preferably Cs⁺ or Rb⁺;

M is a divalent metal cation, preferably selected from the group consisting of

Ge²⁺, Sn²⁺ and Pb²⁺; and

X and Y are different halide anions, preferably independently selected from the group consisting of CF, Br-, Γ and F^~;

wherein k is from 0 to 3, wherein, preferably, k is 0.

In some embodiments, said perovskite is methylammonium lead bromide (MAPbBr₃) or formamidinium lead bromide (FAPbBr₃).

In some embodiments, said electrolyte comprises or consists of a liquid electrolyte, a gel electrolyte a solid electrolyte, a combination of a liquid electrolyte and a gel electrolyte, a combination of a liquid electrolyte and a solid electrolyte, a combination of a gel electrolyte and a solid electrolyte, or a combination of a liquid electrolyte, a gel electrolyte and a solid electrolyte.

In some embodiments, said electrolyte comprises LiCF₃S0₃ (Li-triflate) dissolved in trimethylolpropane ethoxylate (TMPE), preferably with a mass ratio of 1 :0.3 TMPE:Li- triflate.

In some embodiments, said ionic liquid comprises or consists of a salt that has a melting point below 100 °C, wherein, preferably, said salt has as cation an ion comprising a positively charged nitrogen atom undergoing four covalent bonds

in its molecular structure, more preferably an ion selected from the group consisting of Ν,Ν,Ν-trimethylbutyl ammonium ion, N-ethyl-N,N-dimethylpropyl ammonium ion, N-ethyl- Ν,Ν-dimethylbutyl ammonium ion, N,N-dimethyl-N-propylbutyl ammonium ion, N-(2- methoxyethyl)-N,N-dimethylethyl ammonium ion, l-ethyl-3 -methyl imidazolium ion, 1- ethyl-2,3 -dimethyl imidazolium ion, l-ethyl-3, 4-dimethyl imidazolium ion, l-ethyl-2,3,4- trimethyl imidazolium ion, l-ethyl-2,3,5-trimethyl imidazolium ion, l-butyl-3- methylimidazolium, N-methyl-N-propyl pyrrolidinium ion, N-butyl-N-methyl-pyrrolidinium ion, N-sec-butyl-N-methylpyrrolidinium ion, N-(2-methoxyethyl)-N-methylpyrrolidinium ion, N-(2-ethoxyethyl)-N-methylpyrrolidinium ion, N-methyl-N-propylpiperidinium ion, N- butyl-N-methyl piperidinium ion, N-sec-butyl-N-methylpiperidinium ion, N-(2- methoxyethyl)-N-methyl piperidinium ion and N-(2-ethoxyethyl)-N-methyl piperidinium ion, more preferably a l-butyl-3-methylimidazolium ion, and as anion an ion selected from the group consisting of [PF₆]^", [PF₃(C₂F₅)₃r, [PF₃(CF₃)₃]^~ [BF₄]^~ [BF₂(CF₃)₂]^", [BF₂(C₂F₅)₂]^", [BF₃(CF₃)r, [BF₃(C₂F₅)r, [B(COOCOO)₂]- [BOBf, [CF₃S0₃]^", [TfT, [C₄F₉S0₃]^", [Νί]^" [(CF₃S0₂)₂N]-, [TFSIf, [(C₂F₅S0₂)₂N]-, [BETI]^~, [(CF₃S0₂)(C₄F₉S0₂)N]-, [(CN)₂N]^", [DCA]^~, [(CF₃S0₂)₃C]^~ and [(CN)₃C]^~ , preferably [PF₆F, [BF₄]^~ or [CF₃S0₃]^_.

In some embodiments, said ionic liquid comprises or consists of a salt that has a melting point below 100 °C, wherein said salt has as cation a phosphonium-based cation, preferably a tetraalkylphosphonium ion, more preferably a tetrabutylphosphonium ion or a tributylmethylphosphonium ion. Preferably, said ionic liquid comprises or consists of tetraalkylphosphonium methanesulfonate, more preferably tetrabutylphosphonium methanesulfonate, or tributylmethylphosphonium methyl sulfate. In some embodiments, said ionic liquid comprises or consists of a salt that has a melting point below 100 °C, wherein said salt has as cation a sulfonium-based cation, preferably a trialkylsulfonium ion or tris(4-tert-butylphenyl)sulfonium ion.

In some embodiments, said ionically conducting material comprises or consists of a polymeric ionically conducting material or a non-polymeric ionically conducting material or a mixture of a polymeric and a non-polymeric ion dissolving material, wherein, preferably, said polymeric ionically conducting material is a polyelectrolyte or is selected from the group consisting of poly(ethylene oxide), poly(propylene oxide), methoxyethoxy-ethoxy-substituted polyphosphazane, polyether-based polyurethane, and combinations thereof, and wherein, preferably, said non-polymeric ionically conducting material is a crown ether. In some embodiments, said inorganic salt comprises as cation a cation selected from the group consisting of Li⁺, Na⁺, K⁺, Rb⁺, Mg⁺, and Ag⁺, and as anion a molecular anion, preferably a molecular anion selected from the group consisting of [CF₃S0₃]^~ [C10₄]^_, [(CFSS0₂)₂N]^~, [PF₆]-, [PF₃(C₂F₅)₃]^", [PF₃(CF₃)₃]-, [BF₄]^", [BF₂(CF₃)₂r, [BF₂(C₂F₅)₂r, [BF₃(CF₃)]^~ [BF₃(C₂F₅)r, [B(COOCOO)₂]-, [BOB]^", [CF₃S0₃]^~ [Tff, [C₄F₉S0₃]^", [Nff, [(CF₃S0₂)₂Nf, [TFSIT, [(C₂F₅S0₂)₂N]- [BETI]^", [(CF₃S0₂)(C₄F₉S0₂)N]- [(CN)₂N]^", [DCAf, [(CF₃S0₂)₃C]^~ and [(CN)₃C]^~, or a molecular anion selected from the group consisting of [PF₆._x(R)x T [BF_4-x(R)x]^", and [RS0₃]^", wherein R is CF₃, C₂F₅, CN or phenyl, more preferably a molecular anion selected from the group consisting of [CF₃S0₃]^~, [PF₆] ^~, and [BF₄]^~.

In some embodiments, said first electrode functions as anode and comprises or consists of a transparent conductive metal oxide, preferably selected from the group consisting of indium doped tin oxide (ITO), fluorine doped tin oxide (FTO), aluminum doped zinc oxide (AZO), Ti0₂, ZnO, Sn0₂, CuO deposited onto ITO, FTO and/or glass and NiO deposited onto ITO, FTO and/or glass, more preferably indium doped tin oxide (ITO) or fluorine doped tin oxide (FTO), and/or wherein said second electrode functions as cathode and comprises or consists of an air-stable metal, preferably selected from the group consisting of Au, Ag, Al and combinations thereof, or consists of an air-unstable metal, preferably Ba, Ca or LiF/Al, encapsulated in such a way that said air-unstable metal does not get in contact with air, or is a silver nanowire electrode or a nanocarbon electrode, wherein, preferably, said first electrode functions as anode and consists of indium doped tin oxide (ITO) and said second electrode functions as cathode and consists of aluminum.

In some embodiments, said light-emitting layer comprises a surfactant or a polymeric not ionically conducting material, preferably polystyrene or poly(methylacrylate), and/or said electrolyte comprises LiCF₃S0₃ (Li-triflate) and/or trimethylolpropane ethoxylate (TMPE), preferably with a mass ratio of 1 :0.3 for TMPE:Li-triflate.

In some embodiments, said light-emitting layer is a homogeneous layer.

In some embodiments, said light-emitting layer only comprises said nanoparticles or quantum dots and said electrolyte.

In some embodiments, said light-emitting layer is not a bulk layer and/or is not a layer prepared by bulk- growth techniques.

In some embodiments, said light-emitting layer has a thickness in the range of from 10 nm to 10 μιη, preferably in the range of from 80 nm to 3 μιη, more preferably in the range of from 80 nm to 200 nm (even more preferably in the range of from 80 nm to 120 nm) or in the range of from 500 nm to 3 μηι (even more preferably in the range of from 1 μιη to 3 μπι).

In some embodiments, the size of said nanoparticles equals the thickness of said light- emitting layer.

In some embodiments, said nanoparticles have a size in the range of from 1 nm to 1 μπι, preferably in the range of from 10 nm to 1 μηι, more preferably in the range of from 80 nm to 200 nm (even more preferably in the range of from 80 nm to 120 nm) or in the range of from 500 nm to 1 μηι.

In some embodiments, said nanoparticles (or said quantum dots) are the only light-emitting material in said light-emitting layer and/or in said light-emitting electrochemical cell. In some embodiments, said nanoparticles (or said quantum dots) function as light-emitters. Preferably, said nanoparticles (or said quantum dots) are in addition involved in charge injection from the electrodes and charge transport within the bulk of the active layer (i.e. within the light-emitting layer).

In some embodiments, said light-emitting layer comprises nanoparticles of different sizes and/or nanoparticles comprising or consisting of different perovskites.

In some embodiments, said light-emitting layer emits light covering the wavelength range of the whole visible range (400-750 nm), a part of the visible range, the whole near infrared range (750-1400 nm), a part of the near infrared range, or a combination thereof. The light emission can be tuned through size control of the nanoparticle/quantum dot via quantum confinement effects (so only widening of the bandgap is possible) or through the chemical composition of the perovskite; iodide based systems can go as low as 1.4 eV, and bromide systems can go over 2.3 eV.

In some embodiments,

- said light-emitting layer separates said first electrode and said second electrode and/or

said light-emitting layer contacts said first electrode or

said light-emitting layer and said first electrode are separated by an interspersed layer between said light-emitting layer and said first electrode, wherein, preferably, said interspersed layer is a poly(3,4-ethylenedioxythiophene) polystyrene sulfonate

(PEDOT:PSS) layer and/or

said light-emitting layer contacts said second electrode and/or

said light-emitting electrochemical cell further comprises one or more spacers for maintaining a predetermined distance between said first electrode and said second electrode.

In some embodiments, said light-emitting layer is located between said first electrode and said second electrode. Preferably, said light-emitting layer is located only between said first electrode and said second electrode.

In a second aspect, the present invention relates to a method of manufacturing a light-emitting electrochemical cell as defined above, said method comprising the steps of

providing a first electrode;

providing a second electrode;

optionally preparing an interspersed layer on said first electrode, wherein, preferably, said interspersed layer is a poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT.PSS) layer;

preparing on said first electrode (or on said interspersed layer) and/or on said second electrode a layer comprising

(i) nanoparticles or quantum dots comprising or consisting of a perovskite, and

(ii) an electrolyte which comprises or consists of an ionic liquid or a mixture of an ionically conducting material and an inorganic salt,

preferably by doctor-blading, spin-coating, or spray-pyrolysis; assembling said first electrode (optionally with said interspersed layer thereon), said second electrode and said layer on said first electrode (or on said interspersed layer) and/or on said second electrode to form a light-emitting electrochemical cell, thus obtaining a light-emitting electrochemical cell comprising

- a first electrode,

- a second electrode, and

- a light-emitting layer,

wherein said light-emitting layer comprises

(i) nanoparticles or quantum dots comprising or consisting of a perovskite, and

and wherein, optionally, said light-emitting layer and said first electrode are separated by an interspersed layer between said light-emitting layer and said first electrode, wherein, preferably, said interspersed layer is a poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS) layer.

As the skilled person will appreciate, by assembling said first electrode, said second electrode and said layer on said first electrode and/or on said second electrode to form a light-emitting electrochemical cell, said first electrode, said second electrode and said layer on said first electrode and/or on said second electrode are assembled in such a manner that, upon connecting said first and said second electrode to a suitable electrical power supply, said layer is capable of charge injection, charge transport and emission of light, preferably by electroluminescence.

Preferably, said light-emitting electrochemical cell, said first electrode, said second electrode, said light-emitting layer, said nanoparticles, said quantum dots, said perovskite, said electrolyte, said ionic liquid, said mixture of an ionically conducting material and an inorganic salt, said ionically conducting material, said inorganic salt, said charge injection, said charge transport and said light emission are as defined in any of the embodiments above (or as defined by a combination of any of the embodiments described above).

In a third aspect, the present invention relates to the use of a light-emitting electrochemical cell according to the first aspect of the present invention described above or according to any of the embodiments of the above-described first aspect of the present invention or according to a combination of any of the above-described embodiments of the first aspect of the present invention for generating light, wherein, preferably, said use involves applying constant voltage driven and/or pulsed voltage driven and/or current driven schemes to said light- emitting electrochemical cell.

Preferably, said light is generated by electroluminescence.

As used herein, a "perovskite" is a material having a stoichiometry of ABX₃, wherein A stands for a monovalent cation (or more than one different monovalent cation species), B stands for a divalent cation (or more than one different divalent cation species) and X stands for a monovalent anion (or more than one different monovalent anion species), wherein the B cations are in a 6-fold coordination and are surrounded by an octahedron of X anions together with A cations in a 12-fold cuboctahedral coordination. A "metal halide-based perovskite" is a perovskite in which the divalent cations (B) are divalent metal cations (such as Sn²⁺, Pb²⁺ or Ge ) and the monovalent anions (X) are halide anions (such as CI , Br , I or F ). Thus, a metal halide-based perovskite is a perovskite comprising divalent metal cations (such as Sn²⁺, Pb"^T or Ge ), halide anions (such as CI , Br , I or F ), and monovalent cations (i.e. one or several species of monovalent cations). Preferably, the metal halide-based perovskites used in the present invention are composed of monovalent organic cations and/or alkali cations, divalent metal cations, and halide anions. As used herein, an "organo-metal halide perovskite" is a perovskite in which the monovalent cations (A) are organic cations, the divalent cations (B) are divalent metal cations (such as Sn²⁺, Pb²⁺ or Ge²⁺), and the monovalent anions (X) are halide anions (such as Cl^~, Br^", Γ or F^~). A "2D hybrid of a perovskite with an organic material" is composed of alternating layers of single metal-halide octahedra and organic material layers forming a lamella structure.

A "3D hybrid of a perovskite with an organic material" is composed of alternating layers of a perovskite as defined above composed of one or more repeating units in thickness and organic material layers forming a lamella structure. As used herein, a "quantum dot" is a nanoparticle of a smaller size than the exciton bohr radius of the semiconductor. Experimentally, a nanoparticle of a smaller size than the exciton bohr radius of the semiconductor can be identified by comparing a nanoparticle made from a semiconductor with bulk material of the same structure and chemical composition. If the nanoparticle shows a wider bandgap than the bulk material, then this shows that the nanoparticle is small enough to fall under the exciton bohr radius. As used herein, an "ionic liquid" is a salt having a melting point below 100 °C. Examples of such ionic liquids include, but are not limited to, l-butyl-3-methylimidazolium tetrafluoroborate, tetrabutylammonium hexafluorophosphate, tributylmethylphosphonium methyl sulfate and triethylsulfonium bis(trifluoromethylsulfonyl)imide.

If the present application refers to a melting point of a certain temperature, this refers to the melting point at a pressure of 1.01325 ^χ 10⁵ Pa.

An "ionically conducting material", as used herein, is a material, in which one or more types of ions are able to be transported through, for example, via coordination of the ions with peripheral oxygen and nitrogen atoms. If the present invention uses a polymer as ionically conducting material, typically the polymer will interact with the cation of an ion pair and as a consequence become ionically conducting. Examples of such ionically conducting materials include, but are not limited to, poly(ethylene oxide), poly(propylene oxide), methoxyethoxy- ethoxy substituted polyphosphazane, poly-ether based poly-urethane, and crown ethers.

If the present invention indicates that in a certain layer "both charge transport and light emission occur", this designates a situation where, upon driving the device, the movement of ions towards the electrodes allows charge injection and transport processes via stabilization of p- and n-doped regions at the interface of the electrodes, leaving a centered non-doped region in which the charge recombination leads to an emission process.

If the present application indicates that a certain layer is a homogeneous layer, this is meant to designate that the components of which said layer consists are distributed homogeneously within said layer.

If the present application refers to "assembling said first electrode, said second electrode and said layer on said first electrode and/or on said second electrode to form a light-emitting electrochemical cell", this is meant to refer to a step of "forming a light-emitting electrochemical cell by assembling said first electrode, said second electrode and said layer on said first electrode and/or on said second electrode".

If the present invention refers to "room temperature", this is meant to designate a temperature of 25 °C.

As used herein, a "molecular ion" is an ion composed of two or more atoms linked by covalent bonds or composed of a metal complex that can be considered to be acting as a single unit. Examples of molecular ions are [CF₃S0₃] , [(CFSS0₂)₂N] , [PF₆] , [PF₃(C₂F₅)₃] , [BF₄f and [(CN)₃C]^~.

As used herein, an "air-stable metal" is a metal that does not degrade or undergo any chemical change when exposed to ambient conditions. In contrast, an "air-unstable metal" is a metal that undergoes oxidation and/or chemical degradation when exposed to ambient conditions. "Ambient conditions", as used herein, refers to conditions defined by a temperature of 25 °C, a pressure of 1.01325 10⁵ Pa, and the presence of air with the composition of outside air (which comprises 20.95% oxygen) and a humidity of 60-70%.

If the present invention states that an index i (or j) "is from 0 to 1" this means that i (or j) can take the value of 0, the value of 1, or any value between 0 and 1 (such as 0.1, 0.35 or 0.8). Similarly, if the present invention states that an index k "is from 0 to 3" this means that k can take the value of 0, the value of 3, or any value between 0 and 3 (such as 0.1, 1, 1.35, 1,5, 2 or 2.8).

The inventors have surprisingly found a way to prepare layers that consist of a mixture of perovskite NPs and an ionic-based electrolyte matrix and their application in lighting devices. Moreover, the inventors have surprisingly found that light-emitting electrochemical cells based on such layers show considerable luminances (2 cd/m²) and efficacies (0.015 cd/A) at high stabilities even after keeping the devices under ambient conditions.

The nanoparticles and the quantum dots described above exhibit quantum confinement effects. Moreover, the power output of the above-described light-emitting electrochemical cell (as non-encapsulated device) is only slightly reduced compared to the initial value after at least more than 2 months exposed to ambient conditions - room temperature, room light, and humid air between 1 and 100%.

Furthermore, the light emission of the device can be modified by the composition of the perovskite material in terms of the chemical composition and NP size.

BRIEF DESCRIPTION OF THE FIGURES

In the following, reference is made to the figures, wherein: is a schematic representation of (A) an OLED and (B) a LEC. An OLED consists of multiple layers, each one having a specific function in the device, which are prepared by thermal vacuum evaporation. The injection of electrons is achieved by the use of i) a low work-function metal or ii) an electronically doped electron injection layer, both of them being unstable in air and requiring rigorous encapsulation. On the contrary, a LEC consists of a mixture of an active material and an electrolyte with mobile anions, which are displaced when an external bias is applied. Upon displacement an interfacial field is generated that allows for efficient hole and electron injection from air-stable metals. shows (A) the absorbance and (B) the photoluminescence of two perovskite compounds: methylamrnonium lead bromide (MAPbBr₃) and formamidinium lead bromide (FAPbBr₃). These examples demonstrate the tunability of the light absorption and emission by changing the composition of the compound. Inset of (A): As a consequence of the absorbance characteristics, a solution of

MAPbBr₃ has a yellow appearance under daylight (left), whereas a solution of FAPbBr₃ has an orange appearance.

Inset of (B): Both MAPbBr₃ (left) and FAPbBr₃ show intense green photoluminescence . shows (A) the absorbance and (B) the photoluminescence spectra of QDs based on MAPbBr₃.

Inset of (B): The QDs show light blue photoluminescence. shows experimental data to characterize the prepared perovskite quantum dots.

(A) TEM (Transmission electron microscopy) image of the prepared perovskite QDs.

(B) Size distribution obtained by dynamic light scattering of the perovskite quantum dots in THF one week after preparation. shows (A) the photoluminescence spectra and (B) the time-resolved PL (photoluminescence) dynamics of the mixture of MAPbBr₃ perovskite NPs with the electrolyte matrix in films deposited on quartz slides. Figure 6 shows microscopy data to characterize the perovskite NPs films. AFM top view image (left) and 3D profile plot of perovskite NPs films used for device fabrication.

Figure 7 is a graph showing luminance-current density versus applied voltage of

ITO/PEDOT:PSS(100 nm)/Perovskite NPs (50-60 nm)/Al(90 run) devices. The devices were made with (A) MAPbBr₃ and (B) FAPbBr₃ NPs. (Note: The arrows in the graphs of Figures 7-9 and 11-15 indicate which of the two vertical axes the respective data set relates to.)

Figure 8 is a graph showing luminance-current density versus applied voltage of

ITO/PEDOT:PSS(100 nm)/Perovskite NPs-electrolyte matrix (50-70 nm)/Al(90 nm) devices with (A) MAPbBr₃ and (B) FAPbBr₃ NPs, respectively.

Figure 9 is a graph showing luminance-current density versus applied voltage of

ITO/PEDOT:PSS(100 nm)/Perovskite NPs-electrolyte matrix (100-120 nm)/Al(90 nm) devices with (A) MAPbBr₃ and (B) FAPbBr₃ NPs, respectively.

Figure 10: (A) 3D plot showing the evolution of the electroluminescence spectra during the LIV experiments of ITO/PEDOT:PSS(100 nm)/Perovskite NPs- electrolyte matrix (50-70 nm)/Al(90 nm) devices.

(B) Electroluminescence spectra of ITO/PEDOT:PSS(100 nm)/Perovskite NPs-electrolyte matrix (50-70 nm)/Al(90 nm) devices.

(C) Commission Internationale de L'Eclairage CIE 1931 color space chromaticity diagram in which the device with FAPbBr₃ and MAPbBr₃ NPs are shown.

Figure 11 : (A) Graph showing Current density-luminance versus time of

ITO/PEDOT:PSS(100nm)/MAPbBr₃ NPs-electrolyte matrix (50-70 nm)/Al(90 nm) driven by constant voltage of 5 V.

(B) Graph showing average voltage-luminance versus time of ITO/PEDOT:PSS(100nm)/MAPbBr₃ NPs-electrolyte matrix (50-70 nm)/Al(90 nm) driven by a pulsed current using a block wave at a frequency of 1 kHz with a duty cycle of 50% and an average current density of 230 mA/cm². The inset graph shows the device response during the first minutes under device operation conditions.

(A) Graph showing current density-luminance versus time of ITO/PEDOT:PSS(100nm)/MAPbBr₃ NPs-electrolyte matrix (100-120 nm)/Al(90 nm) driven by constant voltage of 14 V.

(B) Graph showing average voltage-luminance versus time of ITO/PEDOT:PSS(100nm)/MAPbBr₃ NPs-electrolyte matrix (100-120 nm)/Al(90 nm) driven by a pulsed current using a block wave at a frequency of 1 kHz with a duty cycle of 50% and an average current density of 13 mA/cm .

The inset graph shows the device response during the first minutes under device operation conditions.

(A) Graph showing current density-luminance versus time of ITO/PEDOT:PSS(100nm)/FAPbBr₃ NPs-electrolyte matrix (50-70 nm)/Al(90 nm) driven by constant voltage of 6 V.

(B) Graph showing average voltage-luminance versus time of ITO/PEDOT:PSS(100nm)/FAPbBr₃ NPs-electrolyte matrix (50-70 nm)/Al(90 nm) driven by a pulsed current using a block wave at a frequency of 1 kHz with a duty cycle of 50% and an average current density of 280 mA/cm².

(A) Graph showing current density-luminance versus time of ITO/PEDOT:PSS(100nm) FAPbBr₃ NPs-electrolyte matrix (100-120 nm)/Al(90 nm) driven by constant voltage of 16 V

(B) Average Voltage-Luminance versus time of ITO/PEDOT:PSS(100nm)/ FAPbBr₃ NPs-electrolyte matrix (100-120 nm)/Al(90 nm) driven by a pulsed current using a block wave at a frequency of 1 kHz with a duty cycle of 50% and an average current density of 15 mA/cm .

(A, B) Luminance-current density versus applied voltage plot of ITO/PEDOT:PSS(100 nm)/FAPbBr₃ NPs-electrolyte matrix (50-70 nm)/Al(90 nm) device. Graph (A) refers to a fresh device and graph (B) to the same device kept under ambient conditions for two months. (C, D) Electroluminescence spectra of both fresh and two month old devices obtained at the maximum luminance level of their respective LIV assays. Graph (C) and (D) refer to MAPbBr₃ and FAPbBr₃ NPs based devices, respectively.

Figure 16: (A, B) Photoluminescence spectra of fresh and aged under ambient conditions

MAPbBr₃ films where (A) shows the spectra of nanoparticles without the electrolyte matrix and (B) with the inclusion of this element deposited on a glass slide.

(C, D) Photoluminescence spectra of fresh and aged under ambient conditions FAPbBr₃ films where (A) shows the spectra of nanoparticles without the electrolyte matrix and (B) with the inclusion of this element deposited on a glass slide.

Figure 17: (A) Photoluminescence spectra of CsPbX₃ NPs with different halides_, (X=T, Br,

CI) at different temperatures,

(B,C) TEM (Transmission electron microscopy) image of the NPs prepared using CsPbBr₃ (B) and CsPbI₃ (C) synthesized at 170°C.

Figure 18: (A,B) Device architecture (A) and luminance-current density versus applied voltage plot of an ITO/PEDOT:PSS(100 nm)/CsPbBr₃ NPs-electrolyte matrix (50-70 nm)/Al(90 nm) device (B).

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS

For the purpose of promoting an understanding of the principles of the invention, reference will now be made to the preferred embodiments and specific language will be used to describe the same. It will nevertheless be understood that no limitation of the scope of the invention is intended thereby, such alterations and further modifications in the device and methods and such further applications of the principles of the invention as illustrated therein being contemplated as would normally occur now or in the future to one skilled in the art to which the invention relates. Moreover, it is to be understood that features and advantages described with regard to one aspect of the invention may also be implied by other aspects of the invention.

Figure 1 shows a schematic representation of the typical construction of an OLED (Figure 1 A) and an LEC (Figure 1 B).

As can be seen from Figure 1 A, an OLED (Organic Light-Emitting Diode) typically comprises a glass substrate 1 (thickness: d = 1 mm) onto which an ITO anode 2 (d ~ 100 nm) is immobilized. On top of the anode 2, organic layers 3 (d ~ 200 nm), which comprise an emitting layer sandwiched in between a combination of electron and hole injection layer(s) together with electron and hole blocking layer(s) , reside, followed by a metal cathode 4 (d ~ 200 nm) and the encapsulation of the device 5 (d ~ 200 nm).

As can be seen from Figure 1 B, an LEC (light-emitting electrochemical cell) typically comprises a glass substrate 6 (thickness: d = 1 mm) onto which an ITO anode 7 (d ~ 100 nm) is immobilized, followed by a light-emitting layer 8 (d ~ 100 nm up to a few microns) and a metal cathode 9 (d ~ 200 nm).

EXAMPLES

In the following, reference is made to the examples, which are given to illustrate, not to limit the present invention.

Example 1

Synthesis of perovskite nanoparticles

In brief, to a solution of oleic acid and octadecene, octylammonium bromide (as the capping agent) and both methylammonium bromide and lead bromid are added dropwise under heavy stirring.

Synthesis of octylammonium bromide

Octylamine (24.79 mL, 0.15 mol) was added to 200 mL of absolute ethanol in a 500 mL round bottom flask. Hydrobromic acid (5 M, 30 mL, 0.15 mol) was added to the solution under constant stirring. After a reaction time of 1 hour at room temperature, the solvent was removed by rotary evaporation. The product was washed with diethyl ether until the powder became white. Before use, the octylammonium bromide was recrystallized in ethanol at least once.

Synthesis of MAPb rs nanoparticles

A solution of oleic acid (850 mg, 3 mmol) in 20 mL of octadecene was stirred and heated at 80 °C in a 100 ml round bottom flask under a N₂ atmosphere. Then, the capping agent octylammoniumbromide (126 mg, 0.6 mmol) was added to the flask and the solution became cloudy. Lead (II) bromide (367 mg, 1 mmol) which was dissolved in 1 ml of anhydrous DMF at 70 °C was added to the reaction vessel and a clear and colourless solution was formed. Subsequent and dropwise addition of methylammonium bromide (44 mg, 0.4 mmol dissolved in 1 mL of anhydrous DMF) produced a yellow dispersion. Lastly, the nanoparticles were immediately precipitated by addition of anhydrous THF (25 mL). The solution was then centrifuged at 7000 rpm for 10 minutes and then washed with anhydrous THF three more times in order to remove the remaining oleic acid and octadecene. The perovskite quantum dots were collected from the supernatant after each centrifugation step.

Synthesis ofFAPbBrs nanoparticles A solution of oleic acid (170 mg, 0.6 mmol) in 4 mL of octadecene was stirred and heated at 80 °C in a 20 mL vial. Then, capping agent, octylammoniumbromide (25.2 mg, 0.12 mmol) was added to the vial and the solution became cloudy. Lead (II) bromide (73.4 mg, 0.08 mmol) which was dissolved in 200 L of anhydrous DMF at 70 °C was added to the reaction vessel and a clear and colourless solution was formed. Subsequent and dropwise addition of formamidinium bromide (10 mg, 0.08 mmol dissolved in 200 μL of anhydrous DMF) produced a yellow dispersion. Lastly, nanoparticles were immediately precipitated by the addition of anhydrous THF (15 mL). After all reactants were added, the solution was stirred for 45 minutes in the same hot plate but the heater was switched off. The solution was then centrifuged at 7000 rpm for 10 minutes. The nanoparticles were then washed with anhydrous THF three more times in order to remove remaining oleic acid and octadecene.

Synthesis of Perovskite QDs

20 ml of octadecene (ODE) was heated at 80°C in a 100 ml round bottom flask under N₂ atmosphere. Then, capping agents, octylammoniumbromide (OABr, 126 mg, 0.6 mmol) and cetyltrimethylammonium bromide (CTAB, 109.3 mg, 0.3 mmol) were added to the flask and the solution became cloudy. The precursors, PbBr₂ (367 mg, 1 mmol dissolved in 1 ml of anhydrous DMF at 70°C) and methylammonium bromide (44 mg, 0.4 mmol dissolved in 1 ml of anhydrous DMF), were fast injected to the reaction vessel with the hypodermic needles at the same time. The solution became yellow after addition of precursors. Lastly, nanoparticles were formed by addition of anhydrous THF (25 ml). The suspension was centrifuged at 3000 rpm for 10 minutes. The NPs sedimentation and the solution were removed. Subsequently the NPs were redispersed in THF and centrifuge for one more time in order to remove remaining ODE.

Light-emitting electrochemical cells

Double layer light-emitting electrochemical cells were produced, wherein, in the first layer, approximately 100 nm in thickness, Poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) was used to flatten the transparent conducting electrode (in most cases indium tin oxide, ITO), while the second layer with a thickness ranging from 20-120 nm was the luminescent layer. All materials were purchased from Sigma Aldrich and used as received. The devices were prepared as follows. ITO coated glass plates were patterned by conventional photolithography (Naranjo Substrates). The substrates were cleaned by using sequential ultrasonic baths in water-soap, water and 2-propanol solvents. After drying, the substrates were placed in a UV-ozone cleaner (Jetlight 42-220) for 10 min. An 100 nm layer of PEDOT:PSS was doctor-bladed onto the ITO-glass substrate to increase the device preparation yield (400 μηι substrate distance and a speed of 10 mm/s). The luminescent layer comprised perovskite NPs and/or quantum dots, LiCF₃S0₃ and trimethylolpropane ethoxylate (TMPE) with the mass ratio 1 :0.3 for TMPE:LiCF₃S0₃. The mixtures were prepared via ultrasonication of the perovskite material in THF solution (1-2 mg/mL) for 20 min. When referring to control device, the NP suspension was filtered using a polytetrafluorethylene membrane filter with a pore size of 0.45 μιη and, subsequently, deposited via spray-coating onto the PEDOT:PSS layer, achieving a layer with a thickness of 20-100 nm. When referring to the devices with active layer based on NPs-electrolyte matrix, the layers were prepared as follows. A solution of the TMPE:LiCF₃S0₃ matrix with the above-mentioned weight ratio was added to the perovskite suspension and it was ultrasonicated for another 30 min. Finally, the solution was filtered using polytetrafluorethylene membrane filters with a pore size of 0.45 μηι. The active layer can be deposited on the ITO electrodes by any solution-based coating or printing method, such as spin-coating, doctor blade coating, inkjet printing, flexographic printing, screen printing, gravure printing, etc. In these examples, thin layers ranging from 20-40 nm were prepared by using doctor-blading (600 μιη substrate distance and a speed of 10 mm/s) and thick layers from 50-120 nm were prepared by using spray- pyrolysis technique (Ar flow at 1.5 atm and 90 °C drying temperature). These conditions resulted in a homogenous thin films with a thickness of 20, 40, 80, and 120 nm and a roughness less than 5 %, having no apparent optical defects. The latter was determined using a Bruker 'DektakxT' profilometer. Once the active layer was deposited, the samples were transferred to an inert atmosphere glovebox (<0.1 ppm 0 and H₂0, Innovative Technology). The cathode can be sandwiched, sputtered or evaporated onto the exposed surface of the luminescent layer. In our device we used aluminum metal electrodes (90 nm) thermally evaporated using a shadow mask under high vacuum (<lxl0^~6 mbar) using an Angstrom Covap evaporator integrated into the inert atmosphere glovebox. Time dependence of luminance, voltage, and current was measured by applying constant and/or pulsed voltage and current by monitoring the desired parameters simultaneously by using an Avantes spectrophotometer (Avaspec-ULS2048LTEC) calibrated with a white LED in conjunction with an integrating sphere 'Avasphere 30-Irrad' and a Botest OLT OLED Lifetime-Test System. Electroluminescence spectrum was recorded using the above mentioned spectrophotometer. Comparative Example 2

All methods referred to in this example were carried out as described in Example 1 above.

Luminance-current density assays under different applied voltages (LIV) of control devices ITO/PEDOT:PSS(100 nm)/Perovskite NPs(50-70 nm)/Al(90 nm) - i.e., devices without ionic electrolyte - were performed. As shown in Figure 7, the injection voltage, i.e. the voltage at which the current density begins to increase due to the fact that charge injection at the electron interface starts happening, is around 15-16 V independently of the type of perovskite NPs. More importantly, no luminance was noted in this experiment even when constant and pulsed voltage and/or current driving schemes were applied. Finally, no charge injection was detected for devices with active layers featuring thicknesses superior to 50-70 nm at the maximum applied voltage (18 V), while thinner active layers led to shorted devices. This suggests that free charge injection and charge transport processes are produced at only high voltages, owing to the lack of the stabilization of the p- and n-doped regions. As a consequence, the exciton recombination rate might be considered as insignificant in the control devices, leading to no luminance features. Figure 7 displays the luminance-current density versus applied voltage of control devices featuring no electrolyte matrix. Here, a poor charge injection was only observed at higher voltages of around 15 V, but no luminance was observed.

Example 3

All methods referred to in this example were carried out as described in Example 1 above. Figures 2 3 and 4 highlight the successful preparation of both perovskite NPs and QDs based on MAPbBr₃ and FAPbBr₃.

The electroluminescence features of ITO/PEDOT:PSS(100 nm)/Perovskite NPs-electrolyte matrix/ Al(90 nm) devices were investigated. The devices were prepared with both MAPbBr₃ and FAPbBr₃ NPs as described in Example 1. First of all, the spectroscopic and morphology features of the active layer were examined. To this end, steady-state emission spectroscopy technique was used to ensure that the perovskite NPs are not destroyed during film preparation, while the film morphology was studied by means of atomic force microscopy (AFM) technique. In detail, AFM images of perovskite NPs-electrolyte matrix films deposited onto ITO substrate show a homogenous coverage with no particular aggregation and/or phase separation features and all give a similar root-mean-square (RMS) roughness of ca. 5-14 nm. Finally, the emission features of the perovskite NPs films were examined. Figure 5 shows that the addition of the electrolyte matrix does not impact the emission maxima nor the emission decay dynamics compared to bare perovskite NPs films. Hence, it is safe to conclude that the spray pyrolysis deposition method is suitable for device preparation. More interesting, the aforementioned features do not change after keeping the films under air and light ambient conditions for a month, suggesting a remarkable robustness of the perovskite NPs-electrolyte matrix films (Figure 16).

Thus, Figure 5 and 6 illustrate the successful preparation of perovskite NPs-electrolyte matrix films on different substrates like quartz and ITO slides. Figures 8 and 9 depict the luminance-current density versus applied voltage of the ITO/PEDOT:PSS(100 nm)/Perovskite NPs-electrolyte matrix/Al(90 nm) devices. Here, two sets of devices featuring thin (50-70 nm) and thick (100-120 nm) active layers with both MAPbBr₃ and FAPbBr₃ NPs were studied. In contrast to the control devices, LECs with a similar thickness show that the injection voltage is strongly reduced and the luminance clearly increases in parallel with the current density (Figure 8). In particular, they feature injection voltages of around 3-3.5 V (at J > 0.1 mA/cm 2 ) and a maximum brightness of around 1 cd/m 2. Notably, injection voltages of around l l-12 V (at J > 0.1 mA/cm ) and maximum brightness of 1.5 cd/m² were noted for devices with a thick active layer (Figure 9).

The electroluminescence spectra of both perovskite NPs devices are shown in Figure 10. In general, 3D plots of the electroluminescence (EL) during the LIV assays show no change in both the broad shape and the maximum upon increasing the applied voltage. This is also valid under repetitive LIV assays, showing no degradation of the device. In particular, the EL spectra of MAPbBr₃ and FAPbBr₃ NPs devices are centered at 550 and 560 nm, respectively as shown on Figure 10B. This represents a red-shift of 20-30 nm compared to the photoluminescence spectra of the perovskite nanoparticles as shown on Figure 2. This finding has been typically observed in LECs and it is ascribed to stabilization of the excited state due to the polarization effect under the applied high electric field during operation conditions. Regardless of the maximum value, the shape of both EL spectra is similar to the photoluminescence spectra, indicating that the same emission mechanisms are involved. Finally, the CIE 1931 coordinates for the EL spectra of MAPbBr₃ and FAPbBr₃ NPs devices are (0.39, 0.46) and (0.45, 0.50), respectively. As shown in Figure 10, they are best described as green-yellowish emitting devices.

Both the strong reduction of the injection voltage and the stable electroluminescence features highlight the benefit of using mobile anions in the active layer, as only control devices with thin active layers show a poor charge injection at higher voltages than 15 V but no luminance features - please compare Figures 7 and 8. A possible explanation may be that in LECs the external applied voltage induces an accumulation of the mobile ions at the electrode interface, reducing the injection barrier from the air-stable electrodes. In addition, the injected charges are stabilized by the density of ions close to the electrodes, controlling the growth of the p- and n-doped regions. As such, the injected charges can recombine in the nondoped region, producing light emission.

This behavior is also reflected when the devices are driven by constant and/or pulsed voltage and/or current schemes. As an example, the inset graphs in Figures 11 and 12 display the initial response of MAPbBr₃ NPs devices driven by constant voltage and pulsed current. In the earlier, the current density rapidly increases followed by the luminance, reaching values of 65 and 14 mA/cm², as well as 0.25 and 2 cd/m² for devices with thin and thick active layers driven by constant 5 and 14 V, respectively. Furthermore, the efficacy values are low around 0.0018 and 0.015 cd/A for thin and thick devices, respectively. The slow increase of the current is ascribed to the required time to redistribute the mobile ions close to the electrode interface. With the formation of p- and n-type regions near the electrodes, carrier injection is enhanced, leading to a gradually increasing device current and emission intensity. Typically, this driven mode leads to lower and unstable luminance features, as the growing of the doped regions is not prevented. This causes a quick reduction of the thickness of the nondoped lighting zone and a strong quenching of the excitons.

To circumvent this drawback, the growing of the doped regions can be reduced while keeping an efficient charge injection by means of a pulsed current driving scheme. Here, the ultrafast pulsed driving induces on-off cycles, which initially required high applied voltages to keep the required current density. This allows both enough charge injection for exciton formation and a very slow redistribution of the mobile anions at the electrode interface that prevent the growing of the doped regions. As such, the luminance is almost instantaneous and the average voltage decreases over the first minutes and remains constant at short time scales (see inset graphs in Figures 11 and 12). This is caused by the reduction of the injection barriers as ions accumulate at the interface with the electrodes, as well as the reduction of the thickness of the intrinsic layer, requiring less voltage to keep the desired current density. Finally, the slow increase of the average voltage of around 0.2 V at long times is quite likely related to the degradation of the active material. Notably, since the decay profile of the luminance and average voltage are not the same, the luminance decay is primary ascribed as an intrinsic feature of the device mechanism. In detail, the luminance level is almost instantaneous starting from 0.2-0.5 cd/m² to maxima brightness of 1.5-2.5 cd/m², showing efficacy values of up to 0.012 cd/A and stabilities of several hours. The same trends were observed for devices with FAPbBr₃ NPs as shown in Figures 9, 13 and 14.

In sum, Figures 8, 9, 10, 11 and 12 highlight the electroluminescence features of devices prepared with active layers of different thicknesses based on a mixture of MAPbBr₃ NPs in combination with an electrolyte matrix. These examples demonstrated working devices, showing low injection voltages compared to control devices and maximum luminance value of around 2.0 cd/m². In addition, the electroluminescent spectra is similar to the photoluminescence spectra, suggesting similar emission processes. Moreover, Figures 8, 9, 10, 13 and 14 highlight the electroluminescence features of devices prepared with active layers of different thicknesses based on a mixture of FAPbBr₃ NPs in combination with electrolyte matrix. These devices show low injection voltages compared to control devices and maximum luminance value of around 0.8 cd/m . In addition, the electroluminescent spectra is similar to the photoluminescence spectra, suggesting similar emission processes.

The air stability of both MAPbBr₃ and FAPbBr₃ NPs devices was examined. To this end, the devices were stored under ambient conditions for two months. Surprisingly, the device performance seems to be slightly affected as shown in Figure 15. On the one hand, the shape and maximum of the electroluminescence spectra remain unaltered in good agreement with the photoluminescence features of the perovskite NP films stored under ambient conditions. On the other hand, the maximum luminance and efficacy levels are slightly reduced. This is quite likely caused by an unbalanced electron-hole recombination, since the active layer slightly degrades over time under ambient conditions.

Thus, Figure 15 confirms the robustness of the perovskite NPs-based devices when they are stored under ambient conditions.

Example 4

Perovskite nanoparticles according to the present invention were prepared using the monovalent alkali metal cesium (Cs) and lead (Pb) as cations. The possible halides iodine, bromine and chlorine were tested as anions. To this end, a Cs-oleate was added to a solution of octadecene, PbX₂ with (X=I, Br, CI), oleylamine (OLA) and oleic acid (OA). The OLA and the OA had previously been dried. The photoluminescence spectra of the nanoparticles prepared with the considered stoichiometry CsPbX₃ with (X=I, Br, CI) were investigated. Finally, transmission electron microscopy (TEM) images of the prepared NPs were obtained.

The synthesis of CsPbX₃ nanoparticles

Preparation of Cs-oleate: 0.814 g of cesium carbonate (Cs₂C0₃), 40 ml of octadecene (ODE) and 2.5 ml of oleic acid (OA) were loaded into a 250ml 3 -neck flask and dried under vacuum for 1 hour at a temperature of 120°C. Then, the solution was heated under N₂ atmosphere to 150°C until the cesium carbonate reacted with the oleic acid.

Drying oleylamine (OLA) and OA:

The oleylamine and the oleic acid were dried under vacuum for 2 h at 120°C.

Synthesis of CsPb∑3 nanoparticles

5 ml of octadecene (ODE) and 0.188 mmol of PbX_{2 ,} (X=I, Br, CI) or their mixtures were loaded into a 100 ml 3-neck flask and dried under vacuum for 1 h at 120°C. Dried oleylamine (OLA, 0.5 mL) and dried OA (0.5 mL) were injected into the flask at 120°C under a N₂ atmosphere. After all PbX₂ was solubilized, the temperature was increased to 140-200°C and the Cs-oleate solution (0.4 mL, prepared as described above) was quickly injected and the reaction mixture was cooled by ice-water bath. For CsPbCl₃, a higher temperature of 150°C and 1 mL of tricotylphosphine (TOP) are required to solubilize PbCl₂. The crude solution was centrifuged at 10000 rpm for 10 min and redispersed in hexane or toluene.

Figure 17A shows the photoluminescence spectra of CsPbX₃ NPs with different halides (X=T, Br, CI) at different temperatures. It can be noted that for a given halide, the temperature affects the wavelength at which the maximum intensity is achieved. TEM pictures of CsPbBr₃ and CsPbI₃ NPs synthesized at 170°C are respectively shown in Figures 17B and 17C to highlight their successful preparation.

Example 5

All methods referred to in this example were carried out as described in Examples 1 and 4 above. The CsPbX₃ NPs prepared according to example 4 were used in the preparation of the active layer in the multilayer architecture of LECs according to the present invention. This active layer of CsPbX₃ NPs was deposited on PEDOT:PSS layer by a spin-coating method. The luminance and the current density of the prepared devices was studied as a function of applied voltage.

Implementation of NPs into LECs

The synthesized CsPbX₃ NPs were applied into the LECs as the active layer thereof. The device architecture is seen in Figure 18 A. The anion was formed by the injected electrons provided by an aluminum electrode and the cation was formed by holes provided by an ITO electrode.

Fabrication of LECs

Indium Tin Oxide (ITO) substrates were cleaned by acetone and isopropanol and placed in an UV-ozone cleaner for 8 min. A PEDOT:PSS layer was spin-coated on the ITO substrates at 1500rpm for 45 s (1500rpm, 45s, 50μΕ). The luminescent layer comprising CsPbBr₃ NPs and trimethylolpropane ethoxylate (TMPE) with ratio of 7.5:1 in hexane was spin-coated at 1000 rpm for 30 s. Later, the samples were transferred into an inert atmosphere glovebox and an Aluminum electrode (90 nm) was thermally evaporated using a shadow mask under high vacuum (<lxl0-6 mbar) using an Angstrom Covap evaporator integrated into the inert atmosphere glovebox.

Figure 18B shows the luminance and the current density of the light-emitting electrochemical cells prepared using CsPbX₃ NPs as a function of the applied voltage. They feature low injection voltages of around 3.5 V and a maximum brightness of around 3 cd/m², clearly exceeding the performance measured in previous examples (compare to Fig. 8, 9 and 15). REFERENCES

Bader, A. J. N., A. A. Ilkevich, I. V. Kosilkin, and J. M. Leger, Nano Lett. 2011, 11, 461.

Costa, R. D., E. Orti, H. Bolink, F. Monti, G. Accorsi, N. Armaroli, Angew. Chem., Int. Ed. 2012, 51, 8178.

Itoh, N., Materials 2010, 3, 3729. Meier, S. B., D. Tordera, A. Pertegas, C. Roldan-Carmona, E. Orti, H. J. Bolink, Materials Today 2014, 77, 217.

Pei, Q., G. Yu, C. Zhang, Y.Yang, A. J. Heeger, Science 1995, 269, 1086.

Pei, Q. B., Y. Yang, G. Yu, C. Zhang, A. J. Heeger, J. Am. Chem. Soc. 1996, 118, 3922.

Qian, G., Y. Lin, G. Wantz, A. R. Davis, K. R. Carter and J. J. Watkins, Adv. Funct. Mater. 2014, 24, 4484.

Yueqing, L., T. Feng, Y. Hou, Z. Lou and Y. Wang, Appl. Phys. Letters 2009, 95, 101 105/1- 101 105/3.

Claims

1. A light-emitting electrochemical cell comprising

- a first electrode,

- a second electrode, and

- a light-emitting layer,

wherein said light-emitting layer comprises

(i) nanoparticles or quantum dots comprising or consisting of a perovskite,

wherein said perovskite is a metal halide-based perovskite,

wherein, preferably, said metal halide-based perovskite is a perovskite composed of

- monovalent organic cations and/or alkali cations,

- divalent metal cations, and

- halide anions,

and

2. The light-emitting electrochemical cell according to claim 1, wherein said perovskite has the stoichiometry

A1.iBM.y /X3-jfcY*, wherein

(ii) a secondary ammonium cation [HaNR^²]*, wherein R¹ and R² are the same or different and are each independently selected from the group consisting of a Ci-C₂₀ alkyl group and an aryl group,

(iii) a tertiary ammonium cation [HNR¹R²R³]⁺, wherein R¹, R² and R³ are the same or different and are each independently selected from the group consisting of a Ci-C₂₀ alkyl group and an aryl group, (iv) a cation having the structure represented by Formula (I)

H

^Rl"N^Nf ^R4 Formula (I),

I I

R2 _R3 wherein R¹, R², R³ and R⁴ are the same or different and are each independently selected from the group consisting of a hydrogen atom, a Ci- C₂o alkyl group and an aryl group,

(v) a cation having the structure represented by Formula (II)

Formula (II),

wherein R¹, R², R³, R⁴, R⁵ and R⁶ are the same or different and are each independently selected from the group consisting of a hydrogen atom, a C_\- C₂₀ alkyl group and an aryl group, wherein, preferably, said cation is guanidinium, and

(vi) an alkali metal cation, more preferably Cs⁺ or Rb⁺;

M and N are different divalent metal cations, preferably independently selected from the group consisting of Ge²⁺, Sn²⁺ and Pb²⁺; and

X and Y are different halide anions, preferably independently selected from the group consisting of Cf, Br^~, Γ and F^~;

wherein i is from 0 to 1, wherein, preferably, i is 0;

wherein j is from 0 to 1, wherein, preferably, j is 0; and

wherein k is from 0 to 3, wherein, preferably, k is 0.

3. The light-emitting electrochemical cell according to any of claims 1 or 2, wherein

(a) said perovskite has the stoichiometry Α ,Β,ΜΧ, wherein

(i) a primary ammonium cation [FFjNR¹]*, wherein R¹ is independently selected from the group consisting of a Q-C^ alkyl group and an aryl group, 1 2 *†" 1 2

(ii) a secondary ammonium cation [H₂NR R ] , wherein R and R are the same or different and are each independently selected from the group consisting of a Q-C20 alkyl group and an aryl group,

1 2 3 + 1 3

(iii) a tertiary ammonium cation [HNR R R ] , wherein R , R and R are the same or different and are each independently selected from the group consisting of a C₁-C₂₀ alkyl group and an aryl group,

(iv) a cation having the structure represented by Formula (I)

H

^R1^ ^ ' ^R Formula (I),

R² R³ wherein R¹, R², R³ and R⁴ are the same or different and are each independently selected from the group consisting of a hydrogen atom, a Ci-C₂o alkyl group and an aryl group,

(v) a cation having the structure represented by Formula (II)

Formula (II),

wherein R¹, R², R³, R⁴, R⁵ and R⁶ are the same or different and are each independently selected from the group consisting of a hydrogen atom, a Cj-C₂o alkyl group and an aryl group, wherein, preferably, said cation is guanidinium, and

(vi) an alkali metal cation, more preferably Cs⁺ or Rb⁺;

M is a divalent metal cation, preferably selected from the group consisting of

Ge²⁺, Sn²⁺ and Pb²⁺; and

X is a halide anion, preferably selected from the group consisting of CF, Br-, Γ and F^_;

wherein i is from 0 to 1, wherein, preferably, i is 0; or said perovskite has the stoichiometry ΑΜι-,Ν,-Χ, wherein

A is a monovalent cation, preferably selected from the group consisting of (i) a primary ammonium cation [FFsNR¹]^-1", wherein R¹ is selected from the group consisting of a Ci-C₂₀ alkyl group and an aryl group,

(ii) a secondary ammonium cation [H₂NR 1 R 2 ] "t~ , wherein R 1 and R 2 are the same or different and are each independently selected from the group consisting of a Ci-C₂₀ alkyl group and an aryl group,

(iii) a tertiary ammonium cation [FTNR R R ] , wherein R , R and R are the same or different and are each independently selected from the group consisting of a Ci-C₂₀ alkyl group and an aryl group,

(iv) a cation having the structure represented by Formula (I)

H

ί^Ν Formula (I),

I I

R² R³ wherein R¹, R², R³ and R⁴ are the same or different and are each independently selected from the group consisting of a hydrogen atom, a C[-C₂o alkyl group and an aryl group,

(v) a cation having the structure represented by Formula (II)

Formula (II),

(vi) an alkali metal cation, more preferably Cs⁺ or Rb⁺;

wherein j is from 0 to 1, wherein, preferably, j is 0; or (c) said perovskite has the stoichiometry ΑΜΧ^Υ* , wherein

A is a monovalent cation, preferably selected from the group consisting of

(i) a primary ammonium cation [H^NR¹]*, wherein R^l is selected from the group consisting of a Q-Qo alkyl group and an aryl group,

(ii) a secondary ammonium cation [H₂NR 1 R2 ]+ , wherein R 1 and R 2 are the same or different and are each independently selected from the group consisting of a Cj-C₂o alkyl group and an aryl group,

(iii) a tertiary ammonium cation [HNR 1 R2 R 3 ]+ , wherein R 1 , R2 and R are the same or different and are each independently selected from the group consisting of a C₁-C₂₀ alkyl group and an aryl group,

(iv) a cation having the structure represented by Formula (I)

H

^R N^ '^R4 Formula (I),

I I

R2 _R3 wherein R¹, R², R³ and R⁴ are the same or different and are each independently selected from the group consisting of a hydrogen atom, a Ci-C₂o alkyl group and an aryl group, or

(v) a cation having the structure represented by Formula (II)

Formula (II),

wherein R¹, R², R³, R⁴, R⁵ and R⁶ are the same or different and are each independently selected from the group consisting of a hydrogen atom, a Ci-C₂₀ alkyl group and an aryl group, wherein, preferably, said cation is guanidinium, and

(vi) an alkali metal cation, more preferably Cs⁺ or Rb⁺;

M is a divalent metal cation, preferably selected from the group consisting of

Ge²⁺, Sn²⁺ and Pb²⁺; and

X and Y are different halide anions, preferably independently selected from the group consisting of Cl^~, Br^", Γ and F^~;

wherein k is from 0 to 3, wherein, preferably, k is 0.

4. The light-emitting electrochemical cell according to any of claims 1 to 3, wherein said electrolyte comprises or consists of a liquid electrolyte, a gel electrolyte a solid electrolyte, a combination of a liquid electrolyte and a gel electrolyte, a combination of a liquid electrolyte and a solid electrolyte, a combination of a gel electrolyte and a solid electrolyte, or a combination of a liquid electrolyte, a gel electrolyte and a solid electrolyte.

5. The light-emitting electrochemical cell according to any of claims 1 to 4, wherein said ionic liquid comprises or consists of a salt that has a melting point below 100 °C, wherein, preferably, said salt has as cation an ion comprising a positively charged nitrogen atom undergoing four covalent bonds

I +

— —

I

in its molecular structure, more preferably an ion selected from the group consisting of Ν,Ν,Ν-trimethylbutyl ammonium ion, N-ethyl-N,N-dimethylpropyl ammonium ion, N- ethyl-N,N-dimethylbutyl ammonium ion, N,N-dimethyl-N-propylbutyl ammonium ion, N-(2-methoxyethyl)-N,N-dimethylethyl ammonium ion, 1 -ethyl-3 -methyl imidazolium ion, l-ethyl-2,3 -dimethyl imidazolium ion, 1 -ethyl-3, 4-dimethyl imidazolium ion, 1- ethyl-2,3,4-trimethyl imidazolium ion, l-ethyl-2,3, 5-trimethyl imidazolium ion, 1-butyl- 3-methylimidazolium, N-methyl-N-propyl pyrrolidinium ion, N-butyl-N-methyl- pyrrolidinium ion, N-sec-butyl-N-methylpyrrolidinium ion, N-(2-methoxyethyl)-N- methylpyrrolidinium ion, N-(2-ethoxyethyl)-N-methylpyrrolidinium ion, N-methyl-N- propylpiperidinium ion, N-butyl-N-methyl piperidinium ion, N-sec-butyl-N- methylpiperidinium ion, N-(2-methoxyethyl)-N-methyl piperidinium ion and N-(2- ethoxyethyl)-N-methyl piperidinium ion, more preferably a l-butyl-3- methylimidazolium ion, and as anion an ion selected from the group consisting of [PF₆]-, [PF₃(C₂F₅)₃]^", [PF₃(CF₃)₃]-, [BF₄]^", [BF₂(CF₃)₂]^~ [BF₂(C₂F₅)₂]-, [BF₃(CF₃)]^~, [BF₃(C₂F₅)]- [B(COOCOO)₂]-, [BOBf, [CF₃S0₃f, [TfT, [C₄F₉S0₃]-, [Nff, [(CF₃S0₂)₂Nr, [TFSir, [(C₂F₅S0₂)₂N]-, [BETFf, [(CF₃S0₂)(C₄F₉S0₂)N]^", [(CN)₂N]^" [DCAf, [(CF₃S0₂)₃C]^~ and [(CN)₃C]^", more preferably [PF₆]^~ [BF₄f or [CF₃S0₃]^~, or wherein, preferably, said salt has as cation a phosphonium-based cation, more preferably a tetraalkylphosphonium ion, more preferably a tetrabutylphosphonium ion or tributylmethylphosphonium ion, wherein, more preferably, said ionic liquid comprises or consists of tetraalkylphosphonium methanesulfonate, more preferably tetrabutylphosphonium methanesulfonate or tributylmethylphosphonium methyl sulfate, or wherein, preferably, said salt has as cation a sulfonium-based cation, more preferably a trialkylsulfonium ion or tris(4-tert-butylphenyl)sulfonium ion.

6. The light-emitting electrochemical cell according to any of claims 1 to 5, wherein said ionically conducting material comprises or consists of a polymeric ionically conducting material or a non-polymeric ionically conducting material or a mixture of a polymeric and a non-polymeric ion dissolving material, wherein, preferably, said polymeric ionically conducting material is selected from the group consisting of poly(ethylene oxide), poly(propylene oxide), methoxyethoxy-ethoxy-substituted polyphosphazane, polyether-based polyurethane, and combinations thereof, and wherein, preferably, said non-polymeric ionically conducting material is a crown ether.

7. The light-emitting electrochemical cell according to any of claims 1 to 6, wherein said inorganic salt comprises as cation a cation selected from the group consisting of Li⁺, Na⁺, K⁺, Rb⁺, Mg⁺, and Ag⁺, and as anion a molecular anion, preferably a molecular anion selected from the group consisting of [CF₃S0₃]^_, [C10₄f, [(CFSS0₂)₂N]^"", [PF₆]^~ [PF₃(C₂F₅)₃]-, [PF₃(CF₃)₃]-, [BF₄]^~, [BF₂(CF₃)₂f, [BF₂(C₂F₅)₂]^{^}, [BF₃(CF₃)]-, [BF₃(C₂F₅)r, [B(COOCOO)₂r, [BOB]^", [CF₃S0₃]-, [TfJ^", [C₄F₉S0₃]^~, [Nff, [(CF₃S0₂)₂N]-, [TFSir, [(C₂F₅S0₂)₂Nr, [BETI]^~, [(CF₃S0₂)(C₄F₉S0₂)N]^", [(CN)₂N]^~, [DCA]^~, [(CF₃S0₂)₃C]^~ and [(CN)₃CT, or a molecular anion selected from the group consisting of [PF_6-x(R)_xf [BF_4-X(R)_X]^", and [RS0₃]^", wherein R is CF₃, C₂F₅, CN or phenyl, more preferably selected from the group consisting of [CF₃S0₃]^~, [PF₆]^~, and [BF₄]-.

8. The light-emitting electrochemical cell according to any of claims 1 to 7, wherein said first electrode functions as anode and comprises or consists of a transparent conductive metal oxide, preferably selected from the group consisting of indium doped tin oxide (ITO), fluorine doped tin oxide (FTO), aluminum doped zinc oxide (AZO), Ti0₂, ZnO, Sn0₂, CuO deposited onto ITO, FTO and/or glass and NiO deposited onto ITO, FTO and/or glass, more preferably indium doped tin oxide (ITO) or fluorine doped tin oxide (FTO), and/or wherein said second electrode functions as cathode and comprises or consists of an air-stable metal, preferably selected from the group consisting of Au, Ag, Al and combinations thereof, or consists of an air-unstable metal, preferably Ba, Ca or LiF/Al, encapsulated in such a way that said air-unstable metal does not get in contact with air, or is a silver nanowire electrode or a nanocarbon electrode,

wherein, preferably, said first electrode functions as anode and consists of indium doped tin oxide (ITO) and said second electrode functions as cathode and consists of aluminum.

9. The light-emitting electrochemical cell according to any of claims 1 to 8, wherein said light-emitting layer comprises a surfactant or a polymeric not ionically conducting material, preferably polystyrene or poly(methylacrylate), and/or

wherein said electrolyte comprises LiCF₃S0₃ (Li-triflate) dissolved in trimethylolpropane ethoxylate (TMPE), preferably with a mass ratio of 1/0.1/0.03 for pero vskite nanoparticles : TMPE : Li-triflate .

10. The light-emitting electrochemical cell according to any of claims 1 to 9, wherein said light-emitting layer comprises nanoparticles or quantum dots of different sizes such that light-emitting layer emits light covering the wavelength range of the whole visible range (400-750 nm), a part of the visible range, the whole near infrared range (750-1400 nm), a part of the near infrared range, or a combination thereof.

11. The light-emitting electrochemical cell according to any of claims 1 to 10, wherein

said light-emitting layer separates said first electrode and said second electrode and/or

said light-emitting layer contacts said first electrode or

said light-emitting layer and said first electrode are separated by an interspersed layer between said light-emitting layer and said first electrode, wherein, preferably, said interspersed layer is a poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS) layer and/or

said light-emitting layer contacts said second electrode and/or

12. A method of manufacturing a light-emitting light-emitting electrochemical cell as defined in any of claims 1 to 11, said method comprising the steps of

providing a first electrode;

providing a second electrode; optionally preparing an interspersed layer on said first electrode, wherein, preferably, said interspersed layer is a poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS) layer;

(i) nanoparticles or quantum dots comprising or consisting of a perovskite, wherein said perovskite is a metal halide-based perovskite,

- monovalent organic cations and/or alkali cations,

- divalent metal cations and

- halide anions, and

preferably by doctor-blading, spin-coating, or spray-pyrolysis;

assembling said first electrode (optionally with said interspersed layer thereon), said second electrode and said layer on said first electrode (or on said interspersed layer) and/or on said second electrode to form a light-emitting electrochemical cell, thus obtaining a light-emitting electrochemical cell comprising

- a first electrode,

- a second electrode, and

- a light-emitting layer,

wherein said light-emitting layer comprises

- monovalent organic cations and/or alkali cations,

- divalent metal cations, and

- halide anions,

and

(ii) an electrolyte which comprises or consists of an ionic liquid or a mixture of an ionically conducting material and an inorganic salt, and wherein, optionally, said light-emitting layer and said first electrode are separated by an interspersed layer between said light-emitting layer and said first electrode, wherein, preferably, said interspersed layer is a poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS) layer.

13. Use of a light-emitting electrochemical cell according to any of claims 1 to 11 for generating light, wherein, preferably, said use involves applying constant voltage driven and/or pulsed voltage driven and/or current driven schemes to said light-emitting electrochemical cell.