Hybrid perovskite upconversion materials

Abstract

The present invention relates to hybrid materials comprising: upconversion nanoparticles and inorganic halide perovskite nanoparticles arranged within tube-shaped lead, tin or a mixture thereof salt nanoclusters. The invention also relates to a preparation method for preparing said hybrid material, and to the use of the hybrid material in the photovoltaic industry.

Description

[0001] HYBRID PEROVSKITE UPCONVERSION MATERIALS

[0002] Field of the Invention

[0003] The present invention relates to the area of luminescent upconversion materials . More specifically, the present invention relates to a hybrid material comprising upconversion nanoparticles , perovskite nanoparticles and lead, tin or a mixture thereof nanoclusters , methods for their preparation and uses thereof .

[0004] Background of the Invention

[0005] Photovoltaics is the leading renewable energy harvesting technology . Thus , there is remarkable strive to enhance the light harvesting capability of the state-of-the-art solar cells . The maj or drawback common to all solar cells types is that they utilize only a limited portion of the solar spectrum, mostly in the visible range , as the active semiconductor materials suffer from intrinsic light absorption thresholds . As a result , photons below and above these threshold values do not contribute to the electricity generation . A plausible solution to enhance the performance is to integrate the photovoltaic cell with an upconverting component , capable of harvesting lower energy photons in the infrared ( IR) range and emitting visible light .

[0006] Although this concept was firstly introduced in 1990s , maj or progress in the field has been made in the recent few years . The upconversion layer can be incorporated into solar cell as a separate layer or can be incorporated by doping of upconversion nanoparticles into active layer or electron transfer layer . ( Grazy . et al . ; Solar Energy Materials & Solar Cells 2021 , 230 , 111234 ) .

[0007] In this context , the development of nanoparticles made up of the combination of a suitable crystalline matrix and certain trivalent lanthanide ions (Ln3+) , which are capable of producing efficient upconversion emission ( lanthanide-upconversion nanoparticles , Ln-UCNPs ) , such as for example , NaYF4 doped with rare earth elements such as Er3+, Yb3+and / or Tm3+, has become highly relevant in this field . These NaYF4 : Yb , Er ( Tm) -type formulation materials have been long known for their upconversion effect (Menyuk N . et al . ; Appl . Phys . Lett . , 1972 , 21 , 159 ; Sommerdij k J.L. and Bril A. , Philips Tech. Rev. 1974, 34, 1) and were subsequently obtained in nanometric size (Zeng J. H. et al.; Adv. Mater. 2005, 17, 2119) .

[0008] More recently, upconversion nanoparticles have been assembled with other materials to produce functional nanomaterials with interesting optoelectronic and electrical properties. Among these functional materials, lead halide perovskites have attracted great interest due to their performance as light-harvesting materials for solar cells, since they can absorb the entire visible spectrum and exhibit a high absorption coefficient, charge carrier mobility, and photoconversion efficiency (Roh J. et al. ACS Appl . Mater. Interfaces 2016, 8, 19847: Li J. et al. ACS Appl. Mater. Interfaces 2017, 9, 19176; Schoenauer M. et al. ACS Appl. Energy Mater. 2018, 1, 3537) .

[0009] Estebanez et al. reported the preparation of linear coassemblies of lanthanide-doped upconversion nanoparticles (UCNPs) and lead halide perovskite nanoparticles (LHPNPs) , within an open peapod-like lead sulfate shell (Estebanez N. et al. ; Adv. Funct. Mater. 2020, 30, 2003766) . However, the materials disclosed therein resulted in a relatively low sensitized emission efficiency of the perovskite particles due to a high predominance of radiative versus non-radiative energy transfer process.

[0010] Therefore, there exists an ongoing need to obtain new materials with adequate optical properties to enable improved energy conversion efficiency and stability in photovoltaic devices.

[0011] Brief Description of the Invention

[0012] The authors of the present invention have developed a novel hybrid material, also referred to as colloidal polymer, combining inorganic halide perovskite nanoparticles (LHPNPs) , upconversion nanoparticles (UCNPs) within lead, tin or a mixture thereof salt nanoclusters with superior absorption and emission properties. Surprisingly, the optical properties of perovskite nanoparticles (NPs) are improved leading to a bright green emission under UV light and an enhanced efficiency of the energy transfer from the UCNPs to the LHPNPs.

[0013] Moreover, the authors of the present invention have surprisingly observed that the hybrid material of the invention eventually leads to the preparation of hybrid films with outstanding sensitized emission efficiency along with an excellent morphology and stability according to international summit on organic PV stability ( ISOS ) protocols .

[0014] Therefore , a first aspect of the invention relates to a hybrid material comprising : a ) upconversion nanoparticles of formula MLnF4 : RE+3, wherein M is an alkaline metal , Ln is a lanthanide element or an element located within group 3 of the periodic table and chemically similar to a lanthanide element , and RE+3is an ion of rare earth elements or combinations thereof , b ) inorganic halide perovs kite nanoparticles of formula CsPbXs , wherein X is a halide selected from the group consisting of Cl , Br or I or combinations thereof , c ) tube-shaped metal salt nanoclusters , wherein the metal salt is selected from lead salt , tin salt and a mixture thereof ; wherein said upconversion nanoparticles and said perovs kite nanoparticles have a mean size of less than 20 nm, and wherein said upconversion nanoparticles and said perovs kite nanoparticles are arranged inside the tube-shaped metal salt nanoclusters .

[0015] A second aspect of the invention is related to a film comprising the hybrid material as defined above .

[0016] A third aspect of the invention provides a method for preparing the hybrid material as defined above , comprising the steps of : a . providing a lead precursor solution at a temperature of 50- 350 ° C under an inert atmosphere , b . inj ecting a cesium precursor into the solution of step ( a ) under an inert atmosphere and quenching the resulting mixture to obtain a suspension of inorganic perovskite nanoparticles of formula CsPbXs , wherein X is an halide selected from Cl ,

[0017] Br or I or combinations thereof , having a mean size of less than 20 nm, c . providing a precursor solution of upconversion nanoparticles of formula MLnF4 : RE+3, wherein M is an alkaline metal , Ln is a lanthanide element or an element located within group 3 of the periodic table and chemically similar to a lanthanide element , and RE+3is an ion of rare earth elements or combinations thereof in a solvent , d . subj ecting the solution of step ( c ) to thermal decomposition to obtain a suspension of the upconversion nanoparticles of formula MLnF4 : RE+3, having a mean size of less than 20 nm; e . providing a metal salt nanocluster precursor solution in a first solvent , wherein the metal salt is selected from lead salt , tin salt and a mixture thereof , adding a second solvent , precipitating the metal salt nanoclusters and adding said precipitate to a third solvent to perform an incubation to yield tube-shaped metal salt nanoclusters ; f . mixing the perovs kite nanoparticles obtained in step (b ) with the upconversion nanoparticles obtained in step ( d) and the tube-shaped metal salt nanoclusters obtained in step ( e ) ; incubating the resulting mixture and subj ecting said mixture to centrifugation to isolate the hybrid material .

[0018] A further aspect of the present invention relates to a hybrid material obtainable by means of the method of the present invention, wherein the hybrid material comprises : a ) upconversion nanoparticles of formula MLnF4 : RE+3, wherein M is an alkaline metal , Ln is a lanthanide element or an element located within group 3 of the periodic table and chemically similar to a lanthanide element , and RE+3is an ion of rare earth elements or combinations thereof , b ) inorganic halide perovs kite nanoparticles of formula CsPbXs , wherein X is a halide selected from the group consisting of Cl , Br or I or combinations thereof , c ) tube-shaped metal salt nanoclusters , wherein the metal salt is selected from lead salt , tin salt and a mixture thereof ; wherein said upconversion nanoparticles and said perovs kite nanoparticles have a mean size of less than 20 nm, and wherein said upconversion nanoparticles and said perovs kite nanoparticles are arranged inside the tube-shaped metal salt nanoclusters .

[0019] Finally, another additional aspect of the present invention relates to the use of the hybrid material in the photovoltaic industry .

[0020] Drawings

[0021] Figure 1 shows a Transmission Electron Microscopy (TEM) image of a hybrid material suspension .

[0022] Figure 2 shows a Scanning Electron Microscope ( SEM) image of a hybrid material film .

[0023] Figure 3 shows the emission of a hybrid material film under ultraviolet light .

[0024] Figure 4 is a graph showing transmittance ( % ) of a hybrid material film at different times during a dark storage experiment .

[0025] Detailed Description of the Invention

[0026] As defined above , a first aspect of the invention relates to a hybrid material comprising : a ) upconversion nanoparticles of formula MLnF4 : RE+3, wherein M is an alkaline metal , Ln is a lanthanide element or an analog thereof and RE+3is an ion of rare earth elements or combinations thereof , b ) inorganic halide perovs kite nanoparticles of formula CsPbXs , wherein X is a halide selected from the group consisting of Cl , Br or I or combinations thereof , c ) tube-shaped metal salt nanoclusters wherein the metal salt is selected from lead salt , tin salt and a mixture thereof ; wherein said upconversion nanoparticles and said perovs kite nanoparticles have a mean size of less than 20 nm, and wherein said upconversion nanoparticles and said perovs kite nanoparticles are arranged inside the tube-shaped metal salt nanoclusters .

[0027] As used herein, the term "upconversion" refers to the ability of a certain material to emit a high-energy photon in the ultraviolet-visible- near-infrared range after sequential absorptions of lower energy photons .

[0028] Therefore , the upconversion nanoparticles of the invention have upconversion luminescent properties with emission in the visible- ultraviolet-near-infrared range after multiple excitations with lower energy photons , particularly in the near infrared range .

[0029] As used herein, the term "lanthanide element" refers to a period 6 element of the periodic table selected from La, Ce , Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho , Er, Tm, Yb and Lu, preferably Yb .

[0030] As used herein, the term "analog thereof" in relation to a lanthanide element refers to an element located within group 3 of the periodic table and is chemically similar to a lanthanide element . In a preferred embodiment , the analog element is Y .

[0031] In a preferred embodiment , M is Na or Li . In another preferred embodiment , RE3+is Yb3+, Er3+, Tm3+, Gd3+, Ho3+or mixtures or combinations thereof .

[0032] In a particular embodiment , the upconversion nanoparticles of the invention have a matrix of formula MLnF4 doped with trivalent ions of rare earth elements RE3+or combinations thereof , and where M is an alkaline metal and Ln is a lanthanide element or an analog thereof .

[0033] A non-limiting example of matrix is NaYF4 doped with Yb3+, Er3+, Tm3+, Gd3+or combinations thereof .

[0034] In a particular embodiment , the upconversion nanoparticles of the invention have a core / shell structure . The term "core / shell structure" refers to nanoparticles comprising a core of an inner material and a shell of an outer material . In a more particular embodiment , the upconversion nanoparticles can have the same or a different chemical composition for the inner material of the core and for the outer material of the shell . A non-limiting example of nanoparticles of the invention with a core / shell structure is NaYF4 : RE3+ / NaYF4 : RE3+or NaYF4 : RE3+ / NaYF4 .

[0035] The material of the present invention further comprises perovskite nanoparticles . As used herein, the term "perovskite" refers to a material with a crystal structure following the formula ABX3 . In the subgroup of inorganic metal halide perovs kites , the B cations are divalent ( like Pb2+, or Sn2+) and the A cations are large monovalent alkali metals (most commonly cesium) or small organic cations like methylammonium (MA) or formamidinium ( FA) .

[0036] The inorganic halide perovs kite nanoparticles of the invention have a CsPbXs formula, wherein X is a halide selected from the group consisting of Cl , Br, I or combinations thereof . In a preferred embodiment , X is Br .

[0037] In a preferred embodiment , the formula of inorganic halide perovskite nanoparticle is CsPbBrs .

[0038] Both types of nanoparticles , i . e . , the upconversion nanoparticles and the perovs kite nanoparticles , of the material of the present invention exhibit similar sizes . In particular, the upconversion nanoparticles and the perovs kite nanoparticles of the invention have a mean size of less than 20 nm .

[0039] It should be noted that in the context of the present invention, reference to a "mean size" refers to a mean value calculated from the relevant size being measured for the different nanostructures ( nanoparticles or nanoclusters ) found in the hybrid material of the invention . The mean sizes can be determined by techniques known in the art such as measuring the individual values of a specific dimension ( length, width, diameter ) of at least 100 randomly chosen particles in transmission electron microscopy (TEM) images .

[0040] In a particular embodiment , the upconversion nanoparticles and the perovs kite nanoparticles of the invention have a mean size of less than 18 nm, less than 16 nm, less than 14 nm or less than 12 nm. In another particular embodiment , the upconversion nanoparticles and the perovs kite nanoparticles of the invention have a mean size between 1 and 20 nm, preferably between 2 and 18 nm, more preferably between 5 nm and 15 nm, even more preferably between 8 and 12 nm, most preferably between 9 and 10 nm .

[0041] In a particular embodiment , the upconversion nanoparticles of the present invention have a larger mean size than the perovs kite nanoparticles . In an alternative embodiment , the perovs kite nanoparticles have a larger mean size than the upconversion nanoparticles . In a preferred embodiment , the mean size of the perovs kite nanoparticles and the mean size of the upconversion nanoparticles differ in less than 5 nm, preferably in less than 3 nm, more preferably in less than 2 nm . In another preferred embodiment , the upconversion and the perovs kite nanoparticles of the material of the present invention have the same mean size , more preferably a mean size between 5 and 15 nm, even more preferably between 9 and 10 nm .

[0042] In a particular embodiment , the upconversion nanoparticles and / or the perovs kite nanoparticles of the material of the present invention are monodisperse .

[0043] As used herein, the term "monodisperse" refers to a population of particles having substantially identical size . One of ordinary s kill in the art will realize that particular sizes of nanoparticles , or of nanoclusters , are actually obtained as particle size distributions . For the purpose of the present invention, a "monodisperse" population of particles means that at least about 60% of the particles or, at least 70% of the particles , or at least 80% of the particles or at least 90% of the particles , fall within a specific particle size range .

[0044] In a particular embodiment , the upconversion nanoparticles and / or the perovs kite nanoparticles of the material of the invention can have a cuboid, hexagonal prism, spherical , tetragonal , rhomboid shape or a combination thereof .

[0045] In a particular embodiment , the shape of the upconversion nanoparticles and the shape of the perovs kite nanoparticles are different . In a more particular embodiment , the upconversion nanoparticles have a hexagonal prism shape . In another more particular embodiment , the perovs kite nanoparticles have a cuboid shape . Preferably, the upconversion nanoparticles have a hexagonal prism shape and the perovskite nanoparticles have a cuboid shape .

[0046] In an alternative particular embodiment , the upconversion nanoparticles and the perovs kite nanoparticles have substantially the same shape , preferably the upconversion nanoparticles and the perovskite nanoparticles of the present invention have a cuboid, hexagonal prism or spherical shape .

[0047] The terms "approximately" , "substantially" and "about" as used herein represent an amount close to the stated amount that still performs a desired function or achieves a desired result . For example , the terms "approximately" , "substantially" and "about" may refer to an amount that is within less than 10% of , within less than 5% of , within less than 1% of , within less than 0 . 1% of , and within less than 0 . 01% of the stated amount .

[0048] Throughout the present specification, when a numeric range is indicated herein, both the lower limit and the upper limit are meant to be included in said range .

[0049] Throughout the present specification, the term "lead salt" refers to a salt wherein the oxidation state of the lead atom is preferably +2 .

[0050] Throughout the present specification, the term "tin salt" refers to a salt wherein the oxidation state of the tin atom is preferably +2

[0051] The material of the present invention further comprises tube-shaped metal salt nanoclusters wherein the metal salt is selected from lead salt , tin salt and a mixture thereof .

[0052] In a more particular embodiment , the tube-shaped nanoclusters comprise a 20-100 wt% , preferably a 30-100 wt% , preferably a 40-100 wt% , preferably a 50-100 wt% , preferably a 60-100 wt% , preferably a 70-100 wt% , even more preferably 80-100 wt% of a metal salt , with respect to the total weight of the nanoclusters . In a most preferred embodiment , the nanoclusters comprise a 85-100 wt% of a metal salt, with respect to the total weight of the nanoclusters .

[0053] In a particular embodiment, the tube-shaped nanoclusters are lead salt nanoclusters . Non-limiting examples of lead salts are organic salts such as lead acetate, lead formate or lead oleate, and inorganic salts such as a lead halide, lead sulphate, lead carbonate or lead phosphate.

[0054] In a particular embodiment, the lead salt of the tube-shaped nanoclusters according to the present invention is an inorganic salt. In a more particular embodiment, the lead salt is selected from the group consisting of lead carbonate, lead nitrate, lead sulphate, lead phosphate, lead phosphonate and combinations thereof. In a preferred embodiment, the lead salt is selected from lead carbonate, lead phosphate, lead sulphate and combinations thereof. In a more preferred embodiment, the lead salt is lead sulphate (PbSO4) .

[0055] In a particular embodiment, the tube-shaped nanoclusters are tin salt nanoclusters . Non-limiting examples of tin salts are organic salts such as tin acetate, tin formate or tin oleate, and inorganic salts such as a tin halide, tin sulphate, tin carbonate or tin phosphate.

[0056] In a particular embodiment, the tin salt of the tube-shaped nanoclusters according to the present invention is an inorganic salt. In a more particular embodiment, the tin salt is selected from the group consisting of tin carbonate, tin nitrate, tin sulphate, tin phosphate, tin phosphonate or combinations thereof. In a preferred embodiment, the tin salt is selected from tin carbonate, tin phosphate, tin sulphate and combinations thereof. In a more preferred embodiment, the tin salt is tin sulphate (SnSO4) .

[0057] In a particular embodiment, the nanoclusters metal salt is a mixture of a lead salt and a tin salt. In a more particular embodiment, the weight ratio of the lead salt with respect to the tin salt ranges between 100:1 and 1:100, preferably 10:1 and 1:1.

[0058] As used herein, the term "metal salt nanocluster" refers to a nanostructure, i. e. , a structure with at least one dimension in the nanoscale formed by crystallization and growth of metal salt nanoclusters . As indicated above , the metal salt of the nanoclusters can be a lead salt , a tin salt or a mixture thereof . Preferably, the metal salt of the nanoclusters is a lead salt . After being incubated, the metal salt nanoclusters of the invention have a tubular shape . The terms "tubular" or "tube-shaped" in relation to the metal salt nanoclusters of the material of the present invention are used interchangeably and refer to an elongated hollow structure with a substantially circular cross-section thus resembling a cylinder .

[0059] In a particular embodiment , the tube-shaped metal salt nanoclusters have a mean length ranging from 100 nm to 500 nm as can be determined using TEM, preferably the nanoclusters have a mean length ranging from 100 nm to 350 nm. In a more preferred embodiment , the tube-shaped metal salt nanoclusters are monodisperse , with at least about 60% of the particles or , at least 70% of the particles , or at least 80% of the particles or at least 90% of the particles having a length falling within the specified length range .

[0060] In another particular embodiment , the tube-shaped metal salt nanoclusters have a mean diameter between 10 and 50 nm, preferably between 15 and 30 nm, even more preferably between 15 and 25 nm, as can be determined by using TEM .

[0061] In the context of the present invention the expression "nanocluster length" relates to the longest dimension of a nanocluster . The terms "nanocluster diameter" and "nanocluster width" are used herein interchangeably and relate to the shortest dimension of a nanocluster corresponding to the diameter of a circular cross-section thereof .

[0062] In a particular embodiment , the tube-shaped metal salt nanoclusters have a mean length ranging between 100 and 500 nm and a mean diameter ranging from 10 to 50 nm, resulting in an aspect ratio of the tubeshaped metal salt nanoclusters ranging between 2 to 50 . In a more particular embodiment , the tube-shaped metal salt nanoclusters have a mean length ranging between 100 and 350 nm and a mean diameter ranging from 15 to 25 nm, resulting in an aspect ratio of the tube-shaped metal salt nanoclusters ranging between 4 to 23.

[0063] In a particular embodiment, the hybrid material of the invention exhibits a ratio of upconversion nanoparticle :perovskite nanoparticles: metal salt tube-shaped nanoclusters, between 0.5:l:l and 1:10:0.5, preferably between 1:3:1 and 1:7:1, preferably the ratio is approximately 1:5:1.

[0064] In another particular embodiment, the upconversion nanoparticles and the perovskite nanoparticles are totally surrounded or encapsulated by the tube-shaped metal salt nanoclusters, i. e. , having all their surface covered by the tube-shaped metal salt nanoclusters .

[0065] In a particular embodiment, the upconversion nanoparticles and the perovskite nanoparticles of the material of the present invention are disposed within the tube-shaped metal salt nanoclusters forming linear chains along the length of said nanoclusters .

[0066] In a more particular embodiment, the upconversion nanoparticles and the perovskite nanoparticles are disposed forming single- nanoparticle wide linear chains, two-nanoparticle wide linear chains, or a combination thereof, along the length of a tube-shaped metal salt nanocluster. Preferably, at least 60%, at least 70% at least 80% or at least 90% of the upconversion and the perovskite nanoparticles are disposed forming single nanoparticle wide linear chains along the length of the tube-shaped metal salt nanoclusters .

[0067] In a more particular embodiment, a linear chain comprises one or more sequences of at least two perovskite nanoparticles intercalated between two upconversion nanoparticles. In an even more particular embodiment, a linear chain comprises one or more sequences of at least three perovskite nanoparticles, preferably at least four perovskite nanoparticles, more preferably at least five perovskite nanoparticles intercalated between two upconversion nanoparticles.

[0068] In a particular embodiment, the average inter-particle distance in a linear chain of upconversion nanoparticles and perovskite nanoparticles arranged within a tube-shaped metal salt nanocluster is between 1 and 20 , preferably between 2 and 8 nm . As used herein, the interparticle distance refers to the distance between two adj acent nanoparticle centers .

[0069] The inventors have surprisingly observed that this configuration results in an enhancement of the sensitized emission efficiency of the perovskite . Without wishing to be bound by theory, the authors believe that this rational arrangement of the nanoparticles within the nanoclusters helps to improve the Forster Resonance Energy Transfer ( FRET ) with minimal energy loss .

[0070] Film

[0071] The present invention further provides a film comprising the hybrid material as defined above .

[0072] The film of the present invention can be formed by any suitable film formation technique known in the art . Non-limiting examples of film formation techniques are centrifugal casting, spin casting, spraycoating, dip-coating or spin-coating .

[0073] In a preferred embodiment , the film of the present invention is obtained by means of a spin-coating process . The term "spin-coating" is understood to refer to a specific process used to deposit a uniform thin film on a flat substrate widely known in the field of the present invention . Generally, in "spin coating" , a small amount of coating material is applied to the center of the substrate that rotates at low speed or does not rotate at all . Subsequently, the substrate is rotated at a specific speed to uniformly apply the coating material by centrifugal force .

[0074] In a particular embodiment , the film comprising the hybrid material of the present invention is obtained by a spin-coating process comprising the following steps :

[0075] ( i ) providing a suspension of the hybrid material of the present invention, and

[0076] ( ii ) depositing the suspension of step ( a ) on a substrate by spin- coating to obtain a film.

[0077] In a more particular embodiment, the concentration of the hybrid material in the suspension of step (i) ranges from 0.01 to 1 pg / pL , preferably from 0.05 to 0.1 pg / pL, more preferably from 0.06 to 0.07 pg / pL.

[0078] In another more particular embodiment, the solvent of the suspension of step (i) is an alkane, preferably selected from the group consisting of pentane, hexane, cyclohexane, heptane or mixtures thereof. In an even more particular embodiment, the solvent is hexane.

[0079] In a further more particular embodiment, a total volume of 50 to 500 pL, preferably of 50 to 300 pL, even more preferably about 100 pL of the suspension of step (a) is deposited on the substrate.

[0080] In a more particular embodiment, the substrate of step (ii) is a glass or transparent polymer substrate. Preferably, the transparent polymer substrate is selected from polyethylene, polycarbonate, or combinations thereof. In a most preferred embodiment, the substrate of step (ii) is a glass substrate.

[0081] In a particular embodiment the spin-coating speed of step (ii) is between 100 and 1000 rpm and the time is between 30 and 300 seconds. Preferably, the spin-coating speed is approximately 800 rpm and the time is approximately 120 seconds.

[0082] In a particular embodiment, the spin-coating process further comprises drying the film obtained in step (ii) under vacuum.

[0083] The inventors have surprisingly observed that the hybrid material thin films thus obtained are very uniform on the entire surface of the substrate without any cracks and voids. Moreover, the inventors have surprisingly found that the hybrid material films display an enhanced quantum yield and sensitized emission efficiency of the perovskite nanoparticles which confirms an occurrence of resonance energy transfer ( RET ) between the upconversion and the perovskite nanoparticles .

[0084] In a particular embodiment , the thickness of the film is between 50 nm and 1 pm, preferably between 100 and 500 nm . In a preferred embodiment , the thickness of the film is between 200 and 300 nm, more preferably between 250 and 290 nm . In a most preferred embodiment the thickness of the film is about 270 nm .

[0085] The films of the present invention can be referred to as thin films . In the context of the present invention, the term "thin film" refers to a layer of material , i . e . a film, ranging from fractions of a nanometer to several micrometers in thickness .

[0086] In a particular embodiment , the quantum yield of the perovs kite nanoparticles in the hybrid film of the present invention is higher than 60% , preferably higher than 70% , more preferably higher than 80% . As used herein, the term "quantum yield" refers to the ratio of the number of photons emitted to the number of photons absorbed by the perovs kite .

[0087] In a particular embodiment , the sensitized emission efficiency (T| ) of the perovskite nanoparticles in the film of the present invention is higher than 40% , preferably higher than 50% . As used herein, the term "sensitized emission efficiency" refers to the quantum yield of the energy transfer transition from donors ( i . e . , upconversion nanoparticles ) to acceptors ( i . e . perovskites ) .

[0088] The films of the present invention have an outstanding optical stability . In a particular embodiment , the film retained at least 80% of its initial transmission after 800 h, preferably after 1000 h of dark storage at a relative humidity of 37 ± 13% and a temperature of 16 ± 1

[0089] Method

[0090] In a third aspect , the invention provides a method for preparing a hybrid material according to the present invention, comprising the steps of : a. providing a lead precursor solution at a temperature of 50- 350 °C under an inert atmosphere, b. injecting a cesium precursor into the solution of step (a) under an inert atmosphere and quenching the resulting mixture to obtain a suspension of inorganic perovskite nanoparticles of formula CsPbXs, wherein X is an halide selected from Cl, Br or I or combinations thereof, having a mean size of less than 20 nm, c. providing a precursor solution of upconversion nanoparticles of formula MLnF4 : RE+3, wherein M is an alkaline metal, Ln is a lanthanide element or an element located within group 3 of the periodic table and chemically similar to a lanthanide element and RE+3is an ion of rare earth elements or combinations thereof in a solvent, d. subjecting the solution of step (c) to thermal decomposition to obtain a suspension of the upconversion nanoparticles of formula MLnF4 : RE+3, having a mean size of less than 20 nm; e. providing a metal salt nanocluster precursor solution in a first solvent, wherein the metal salt is selected from lead salt, tin salt and a mixture thereof, adding a second solvent, precipitating the metal salt nanoclusters and adding said precipitate to a third solvent to perform an incubation to yield tube-shaped metal salt nanoclusters; f. mixing the perovskite nanoparticles obtained in step (b) with the upconversion nanoparticles obtained in step (d) and the tube-shaped metal salt nanoclusters obtained in step (e) ; incubating the resulting mixture and subjecting said mixture to centrifugation to isolate the hybrid material.

[0091] Therefore, the method of the present invention comprises a step (a) of providing a lead precursor solution at a temperature of 50-350 C under an inert gas atmosphere.

[0092] In a particular embodiment, the lead precursor solution of step (a) comprises: a lead salt, and

[0093] - at least one surface ligand. The lead salt of step (a) may be any suitable lead salt known in the art. Non-limiting examples of lead salts are organic acid lead salts such as lead oleate or lead halides. In a particular embodiment, the lead salt of step (a) is a lead halide selected from PbC12, PbBr2, Pbl2 or combinations thereof, preferably the lead halide is lead bromide (PbBr2) .

[0094] As used herein, the term "surface ligand" refers to a molecule or ion which binds to the surface of the nanoparticles during the synthesis thereof to stabilize them and compensate for their high surface to- volume ratio. Any surface ligands known in the art may be used. Nonlimiting examples of surface ligands are organic acids and amines .

[0095] In a particular embodiment the at least one surface ligand is an alkylamine, an organic acid or a combination thereof. In a more particular embodiment, the at least one surface ligand is an amine and / or organic acid comprising one or more alkyl chain(s) , such as linear or branched alkyl chains with 2 to 30 carbon atoms, preferably with 5 to 30 carbon atoms. In a particular embodiment, the one or more alkyl chain (s) may be saturated (alkane) or unsaturated (alkene) alkyl chains. Preferably, the one or more alkyl chain (s) are unsaturated alkyl chains, even more preferably comprising at least one double bond in a cis configuration .

[0096] In a preferred embodiment, the at least one surface ligand is an alkylamine selected from the group consisting of cis- and trans-oleyl amine, lauryl amine, octyl amine, dodecyl amine, hexadecyl amine, butyl amine, ethyl amine, and octadecyl amine; an organic acid selected from the group consisting of oleic acid, lauric acid, stearic acid, mysteric acid, or hexadecanoic acid, or a combination thereof. In a more preferred embodiment, the surface ligand is selected from oleyl amine, oleic acid or a mixture thereof.

[0097] In a particular embodiment, the weight ratio of surface ligand(s) to lead salt is between 10:1 and 15:1, preferably 13:1. In a particular embodiment, the lead precursor solution may further comprise a non-coordinating solvent. As used herein, the term "noncoordinating solvent" refers to a solvent that does not contain heteroatoms such as O, S, N or P to coordinate to a nanoparticle surface. The non-coordinating solvent can be a hydrocarbon such as an alkane or an alkene, preferably selected from hexadecane, tetradecane, octadecane, octadecene, squalene or mixtures thereof. Preferably, the noncoordinating solvent is octadecene.

[0098] In a preferred embodiment, the lead precursor comprises:

[0099] - between 0.1 and 3 wt% lead bromide,

[0100] - between 5 and 7 wt% of oleyl amine,

[0101] - between 7 and 10 wt% of oleic acid, and

[0102] - between 80 and 90 wt% of octadene.

[0103] The lead precursor may be obtained by mixing the lead salt and the one or more surface ligands into a non-coordinating solvent. In a preferred embodiment, the lead precursor is obtained by firstly adding the lead salt and secondly adding the one or more surface ligands into the non-coordinating solvent. In a preferred embodiment, the lead precursor is obtained by the addition of lead bromide into octadecene, followed by the addition of oleic acid and oleyl amine in sequence.

[0104] The lead precursor solution of step (a) is provided at a temperature ranging from 50 to 350 °C under an inert atmosphere. In a particular embodiment, the lead precursor solution is provided at a temperature ranging from 100 to 250 °C. In a preferred embodiment, the lead precursor solution of step (a) is provided at a temperature of about 180 °C

[0105] In a particular embodiment, the inert atmosphere may be selected from vacuum, nitrogen, argon or combinations thereof.

[0106] In a more particular embodiment, the solution of step (a) is firstly placed under vacuum and secondly under a nitrogen or argon atmosphere, preferably argon.

[0107] The method of the present invention further comprises a step (b) of injecting a cesium precursor into the solution of step (a) under an inert atmosphere, and quenching the resulting mixture to obtain a suspension of inorganic perovskite nanoparticles of formula CsPbXs, wherein X is a halide selected from Cl, Br or I or combinations thereof, having a mean size of less than 20 nm.

[0108] In a particular embodiment, the cesium precursor comprises an organic or inorganic cesium salt. In a particular embodiment, the cesium salt is an organic cesium salt. In a preferred embodiment, the organic cesium salt is cesium oleate.

[0109] The organic cesium salt may be obtained by any suitable means known in the art. In a particular embodiment, the organic cesium salt may be prepared by adding a desired organic acid, such as oleic acid, to an inorganic cesium salt, such as cesium carbonate, under stirring. In a more particular embodiment, the organic acid is added to the inorganic cesium salt in a molar ratio ranging from 1:1 to 10:1, preferably from 3 : 1 to 5 : 1. In a preferred embodiment, the organic acid is added to the inorganic cesium salt in a molar ratio of about 4:1.

[0110] In a particular embodiment, the cesium precursor may further comprise a non-coordinating solvent. The non-coordinating solvent can be a hydrocarbon such as an alkane or an alkene, preferably selected from hexadecane, tetradecane, octadecane, octadecene or squalene or mixtures thereof. Preferably, the non-coordinating solvent is octadecene .

[0111] In a preferred embodiment, the cesium precursor comprises:

[0112] - between 1 and 10 wt% cesium oleate, and

[0113] - between 90 and 99 wt% octadecene.

[0114] The injection of the cesium precursor into the lead precursor solution allows the nucleation and growth of perovskite nanoparticles in the resulting mixture.

[0115] In a particular embodiment, the cesium precursor is added in a weight ratio ranging from 1:1 to 1:10, preferably 1:3 to 1:5 relative to the lead salt in the lead precursor solution of step ( a ) . In a more particular embodiment , the cesium precursor is added in a weight ratio of about 1 : 4 relative to the lead salt in the lead precursor solution of step ( a ) .

[0116] In a preferred embodiment , the inert atmosphere of step (b ) is argon .

[0117] Upon completion of inj ection of the cesium precursor, the resulting mixture is quenched, thus obtaining a suspension of perovs kite nanoparticles of formula CsPbXs having a mean size of less than 20 nm .

[0118] As used herein, the term "quench" or "quenching" refers to cooling the resulting mixture in conditions suitable to arrest the nanoparticle growth, thus obtaining a suspension of perovskite nanoparticles with a mean size of less than 20 nm .

[0119] In a particular embodiment , this cooling is accomplished by contacting the resulting mixture with a refrigerant fluid such as water, ice / water , ethanol , liquid nitrogen or a mixture thereof , preferably ice / water, even more preferably shattered ice cubes / water .

[0120] In a particular embodiment , the mixture of step (b ) is quenched for a period of at least 5 seconds , preferably at least 10 seconds , more preferably at least 20 seconds . In a more preferred embodiment , the mixture of step (b ) is quenched for a period of about 30 seconds .

[0121] In a particular embodiment , step (b ) further comprises separating the perovs kite nanoparticles obtained, by any means known in the art , such as filtration, decanting or centrifugation .

[0122] In a preferred embodiment , the perovskites nanoparticles of step (b ) are separated by centrifugation . In a more preferred embodiment , the centrifugation is carried out at a centrifugal rotational speed of between 1000 and 5000 rpm, preferably between 2000 and 4000 rpm. In a more particular embodiment , the centrifugation is carried out for a period of 1 to 10 minutes , preferably for a period of about 5 minutes . In a preferred embodiment, the centrifugation is carried out at about 2500 rpm during about 5 minutes.

[0123] The method of the invention further comprises a step (c) of providing a precursor solution of upconversion nanoparticles of formula MLnF4 : RE+3, wherein M is an alkaline metal, Ln is a lanthanide element or an analog thereof and RE+3is an ion of rare earth elements or combinations thereof in a solvent.

[0124] In a particular embodiment, the precursor of the upconversion nanoparticles of formula MLnF4:RE+3comprises:

[0125] - a RE source,

[0126] - a Ln source, and

[0127] -a metal fluoride source.

[0128] Any suitable rare earth (RE) source known in the art may be used. Non-limiting examples of rare earth sources are RE salts such as a RE halide, trifluoroacetate, oleate, acetate. Preferably, the RE source is a RE halide. In a more particular embodiment, the RE source is a rare- earth chloride (RECI3) , preferably selected from Gd, Yb, Tm, Ho chloride or a combination thereof.

[0129] In a particular embodiment, the Ln source is a lanthanide or analog thereof salt. In a preferred embodiment the Ln source is a halide, such as a Ln chloride. In a preferred embodiment, the Ln source is YCI3.

[0130] In a particular embodiment, the metal fluoride source is selected from the group consisting of NaF and NaBF4. In another particular embodiment, the metal fluoride source is a mixture of a fluoride compound such as HF and NH4F and MOH-type base where M is an alkaline metal, such as NaOH, KOH, LiOH or a mixture thereof. The fluoride compound may be selected from HF and NH4F. In a preferred embodiment, the metal fluoride source is a mixture of NH4F and NaOH.

[0131] The solvent of the upconversion nanoparticle precursor may be any solvent or solvent mixture suitable in the art for a thermal decomposition process. As used herein, the term "thermal decomposition" refers to a process widely known in the field of the present invention in which synthetic precursors are dissolved in an organic solvent and later decomposed by applying heat.

[0132] Therefore, in a particular embodiment, the solvent of step (c) is an organic solvent or solvent mixture with a high-boiling point such as an organic solvent with a boiling point of at least 300 °C at atmospheric pressure .

[0133] In a preferred embodiment, the solvent of step (c) is octadecene.

[0134] In a particular embodiment, the solvent or solvent mixture may comprise other additives such as surface ligands. Non-limiting examples of surface ligands are oleic acid, trioctylphosphine oxide, oleylamine or combinations thereof. In a particular embodiment, the surface ligand is an alkylamine such as oleylamine and / or an organic acid such as oleic acid. Preferably, the weight ratio of oleic acid to octadecene is between 1:1 and 1:5, more preferably the weight ratio of oleic acid to octadecene is about 1:2.

[0135] The method of the invention further comprises a step (d) of subjecting the solution of step (c) to thermal decomposition to obtain a suspension of the upconversion nanoparticles of formula MLnF4 : RE+3, having a mean size of less than 20 nm.

[0136] In a particular embodiment, the solution of step (c) is heated to a final temperature between 200-350 °C, preferably at a rate of 5-10 °C / min. In a more particular embodiment, the final temperature is between 280 and 320, preferably between 310 and 320. Even more preferably, the final temperature is of about 320 °C.

[0137] In a particular embodiment, the final temperature is maintained for a period of 1 to 180 minutes, preferably 5 to 60 minutes, more preferably 10 to 30 minutes, even more preferably for a period of about 15 minutes.

[0138] In a most preferred embodiment, the solution of step (c) is heated from room temperature to a final temperature of about 320 °C at a rate of about 8 °C / min and the final temperature is maintained for a period of about 15 min.

[0139] In a particular embodiment, step (d) further comprises separating the upconversion nanoparticles obtained by any means known in the art, such as filtration, decanting or centrifugation.

[0140] In a preferred embodiment, the upconversion nanoparticles of step (d) are separated by centrifugation. In a more preferred embodiment, the centrifugation is carried out at a centrifugal rotational speed of between 8000 and 12000 rpm, preferably about 10000 rpm. In a more particular embodiment, the centrifugation is carried out for a period of about 0.5 to 5 minutes, preferably 1 to 4 minutes, even more preferably about 2 minutes . In a preferred embodiment the centrifugation is carried out at about 10000 rpm for a period of about 2 minutes.

[0141] The method further comprises a step (e) of providing a metal salt nanocluster precursor solution in a first solvent, wherein the metal salt is selected from lead salt, tin salt and a mixture thereof adding a second solvent, precipitating themetai salt nanoclusters, and adding said precipitate to a third solvent to perform an incubation to yield tube-shaped metal salt nanoclusters.

[0142] In a particular embodiment, the metal salt nanocluster precursor comprises :

[0143] - a metal source, and

[0144] - at least one ligand.

[0145] The metal source may be any suitable metal, i.e., lead and / or tin source known in the art to obtain nanoclusters obtained by crystallization and growth of the corresponding metal salt into coordination polymers. In a particular embodiment, the metal source is a lead and / or tin source (e.g., a salt) selected from lead oleate, lead chloride, tin oleate, tin chloride and mixtures thereof.

[0146] In a preferred embodiment, the metal source of the nanocluster precursor is a lead source. In a more preferred embodiment, the lead source is selected from lead oleate or lead chloride. In a more preferred embodiment, the lead source is lead oleate.

[0147] In a particular embodiment, the at least one ligand is selected from an alkyl-ammonium ligand. In a more particular embodiment, the alkyl-ammonium ligand is selected from an alkyl-ammonium sulphate, alkyl-ammonium carbonate, alkyl-ammonium nitrate, alkyl-ammonium phosphate, alkyl-ammonium phosphonate, or mixtures thereof. In a preferred embodiment, the ligand is an alkyl-ammonium sulphate selected from the group consisting of tetrabutylammonium hydrogen sulphate (TBAHS) , oleylammonium sulfate, cyclohexane methylammonium hydrogen sulphate (CHMAHS) or combinations thereof. More preferably, the alkyl- ammonium sulfate is cyclohexane methylammonium hydrogen sulphate (CHMAHS) .

[0148] In a particular embodiment, the molar ratio of the ligand relative to the metal salt in the precursor ranges between 1:1 and 1:5, preferably, the weight ratio of the ligand relative to the metal salt in the precursor is about 1:2.

[0149] In a particular embodiment, the metal salt nanocluster precursor may comprise one or more further ligands such as oleylamine, oleic acid or a mixture thereof.

[0150] In an embodiment, the metal salt of the nanocluster precursor is a lead salt. In a preferred embodiment, the lead salt nanocluster precursor is a lead sulphate nanocluster precursor comprising lead oleate and cyclohexane methylammonium hydrogen sulphate (CHMAHS) , more preferably in a molar ratio between 1:2 and 2:1 even more preferably in a molar ratio of about 1:1.

[0151] In another embodiment, the metal salt of the nanocluster precursor is a tin salt. In another embodiment, the metal salt of the nanocluster precursor is a tin sulphate nanocluster precursor comprising tin oleate and cyclohexane methylammonium hydrogen sulphate (CHMAHS) , more preferably in a molar ratio between 1:2 and 2:1, even more preferably in a molar ratio of about 1:1.4.

[0152] In an embodiment, the metal salt of the nanocluster precursor comprises a mixture of a lead salt and a tin salt. In another preferred embodiment, the metal salt of the nanocluster precursor is a mixture of a lead sulphate precursor and a tin sulphate precursor comprising lead oleate and tin oleate and cyclohexane methylammonium hydrogen sulphate (CHMAHS) , more preferably in a molar ratio of total salt mixture to cyclohexane methylammonium hydrogen sulphate (CHMAHS) between 1:2 and 2:1, more preferably in a molar ratio between 1:2 to 2:1, even more preferably of about 1:1.

[0153] In a more particular embodiment, the weight ratio of the lead salt with respect to the tin salt in the metal salt of the nanocluster precursor ranges between 100:1 and 1:100, preferably 10:1 between and 1:10.

[0154] In a more preferred embodiment, the metal salt nanocluster further comprises oleic acid. In another more preferred embodiment, the molar ratio of metal oleate : cyclohexane methylammonium hydrogen sulphate (CHMAHS) and oleic acid is about 1:1:45. In the case that the metal salt nanocluster is a tin salt nanocluster, the molar ratio of tin olete : cyclohexane methylammonium hydrogen sulphate (CHMAHS) and oleic acid is about 1:1.4:68

[0155] The first solvent may be any solvent known in the art suitable to completely solubilize the metal salt nanocluster precursor. In a particular embodiment, the first solvent is selected from chloroform, dichlorometane, dichloroetane or a mixture thereof, preferably chloroform.

[0156] In a particular embodiment, the concentration of metal source and / or the at least one ligand such as the concentration of alkyl-ammonium ligand in the first solvent ranges from 0.1 to 15 mM, preferably from 0.5 to 10 mM, more preferably from 1 to 5 mM.

[0157] To the solution of the metal salt nanocluster precursor, a second solvent is added and the metal salt nanocluster is precipitated, by any suitable method known by the person skilled in the art, preferably by centrifugation .

[0158] In a preferred embodiment , the metal salt nanoclusters of step ( e ) are separated by centrifugation . In a particular embodiment , the centrifugation is carried out at a centrifugal rotational speed of between 5000 and 15000 rpm, preferably between 8000 and 12000 rpm, even more preferably at about 10000 rpm. In a more particular embodiment the centrifugation is carried out for a period of between 1 and 10 minutes , preferably between 2 and 8 minutes , more preferably about 5 minutes . In a preferred embodiment , the centrifugation is carried out at about 10000 rpm for a period of about 5 minutes .

[0159] The second solvent may be any solvent known in the art suitable to effect precipitation of the metal salt nanoclusters . In a particular embodiment , the second solvent is selected from H2O , acetone , methanol , ethanol , isopropanol or combinations thereof . Preferably, the second solvent is methanol or ethanol , more preferably ethanol .

[0160] In a particular embodiment , the amount of the second solvent added is between 1 and 5 times that of the first solvent . In a more particular embodiment , the amount of the second solvent added is about 3 times that of the first solvent .

[0161] The metal salt nanocluster precipitated is added to a third solvent , to perform an incubation . Under these conditions , self-assembly of metal salt molecules takes places resulting in the formation of tube-shaped nanoclusters .

[0162] The precipitate of step ( e ) is added to a third solvent to redisperse the metal salt nanoclusters and incubated to yield tube-shaped lead salt nanoclusters . In the context of the present invention, the terms "incubated" or "incubating" means leaving the solution undisturbed, i . e . , without stirring .

[0163] The third solvent may be any solvent known in the art suitable to effect incubation of the metal salt nanoclusters . In a particular embodiment , the third solvent is a non-polar solvent , particularly selected from pentane, hexane, cyclohexane, methylcyclohexane, heptane, xylene, toluene or mixtures thereof. Preferably, the solvent is hexane.

[0164] In a particular embodiment, the metal salt nanocluster dispersion of step (e) is incubated for a period of at least 20 hours, preferably for a period of between 24 and 72 hours, preferably for a period of about 24 hours, preferably about 48 hours, preferably for a period of about 72 h.

[0165] In a preferred embodiment, the tube-shaped metal salt nanoclusters obtained in step (e) have a mean length ranging from 100 to 500 nm and a mean width ranging from 10 to 50 nm. In a more preferred embodiment, the tube-shaped metal salt nanoclusters obtained in step (e) have a mean length ranging from 100 to 350 nm and a mean width ranging from 15 to 25 nm.

[0166] In a particular embodiment, step (e) further comprises separating the tube-shaped metal salt nanoclusters obtained after incubation, by any means known in the art, such as filtration, decanting or centrifugation.

[0167] In a preferred embodiment, the tube-shaped metal salt nanoclusters of step (e) are separated by centrifugation. In a particular embodiment, the centrifugation is carried out at a centrifugal rotational speed of between 1000 and 5000 rpm, preferably between 2000 and 4000 rpm, even more preferably at about 2500 rpm. In a more particular embodiment the centrifugation is carried out for a period of between 1 and 10 minutes, preferably between 2 and 8 minutes, more preferably about 5 minutes. In a preferred embodiment, the centrifugation is carried out at about 10000 rpm for a period of about 5 minutes .

[0168] The method of the present invention further comprises a step (f) of mixing the perovskite nanoparticles obtained in step (b) with the upconversion nanoparticles obtained in step (d) and the tube-shaped metal salt nanoclusters obtained in step (e) ; incubating the resulting mixture, and subjecting said mixture to centrifugation to isolate the hybrid material .

[0169] In a particular embodiment, the mixing of the step (f) is performed by adding the perovskite nanoparticles from step (b) , the upconversion nanoparticles from step (d) and the tube-shaped metal salt nanoclusters from step (e) to a solvent selected from hexane, cyclohexane, toluene or mixtures thereof. Preferably, the solvent is hexane.

[0170] Within this embodiment, the perovskite nanoparticles, the upconversion nanoparticles and the tube-shaped metal salt nanoclusters may be simultaneously or sequentially added to the solvent. In a preferred embodiment, the solvent is hexane or cyclohexane.

[0171] In another particular embodiment, the mixing of step (f) comprises combining a suspension of perovskite nanoparticles obtained in step (b) in a first solvent, a suspension of upconversion nanoparticles obtained in step (d) in a second solvent and a suspension of tube-shaped metal salt nanoclusters obtained in step (e) in a third solvent. Within this embodiment, the suspensions may be simultaneously or sequentially combined, such as firstly combining the suspension of perovskite nanoparticles and the suspension of upconversion nanoparticles, and further adding the combined nanoparticles to the tube-shaped metal salt nanoclusters suspension .

[0172] The first, second and third solvents of step (f) may be the same or different solvents or solvent mixtures. In a particular embodiment, the first to third solvents are selected from hexane, cyclohexane, toluene or a mixture thereof. In a more particular embodiment, the first solvent is toluene, the second solvent is cyclohexane and the third solvent is hexane.

[0173] In an alternative embodiment, the first, second and third solvents are the same, preferably hexane or cyclohexane.

[0174] In a particular embodiment, the concentration of perovskite nanoparticles in the first solvent ranges from 50 to 80 mg / mL, preferably about 60 mg / mL. In another particular embodiment, the concentration of upconversion nanoparticles in the second solvent ranges from 50 to 80 mg / mL, preferably about 60 mg / mL. In a further particular embodiment, the concentration of tube-shaped metal salt nanoclusters in the third solvent ranges from 10 to 20 mg / mL, preferably about 15 mg / mL. In a particular embodiment, the weight ratio of the perovskite nanoparticles : upconversion nanoparticles : tube-sahped metal salt nanoclusters in the resulting mixture of step (f) ranges between 1: 0.5:1 and 10:1:0.5, preferably between 3:1:1 and 7:1:1, more preferably is about 5:1:1.

[0175] In a particular embodiment, the mixture of step (f) is incubated for a period of 5 minutes to 120 hours. In a preferred embodiment, the mixture of step (f) is incubated for a period of 8 h to 72 h, preferably for a period of 12 h to 36 h, more preferably for a period of about 24 h. Preferably, the mixture is incubated at room temperature.

[0176] Without wishing to be bound by theory, it is believed that these conditions allow the co-assembly of perovskite and upconversion nanoparticles inside the tubular metal salt nanoclusters, such as intercalated forming linear chains inside the clusters.

[0177] After incubation, the mixture is subjected to centrifugation to separate the hybrid material. In a particular embodiment, the centrifugation is carried out at a centrifugal rotational speed of between 5000 and 10000 rpm, preferably between 6000 and 8000 rpm, even more preferably at about 7000 rpm. In a more particular embodiment, the centrifugation is carried out for a period of about 1 to 10 minutes. In a more preferred embodiment, the centrifugation is carried out at about 7000 rpm for a period of about 5 minutes.

[0178] The present invention further relates to a hybrid material obtainable by means of the method of the present invention in any of its particular and preferred embodiments, wherein the hybrid material comprises : a) upconversion nanoparticles of formula MLnF4 : RE+3, wherein M is an alkaline metal, Ln is a lanthanide element or an element located within group 3 of the periodic table and chemically similar to a lanthanide element and RE+3is an ion of rare earth elements or combinations thereof, b) inorganic halide perovskite nanoparticles of formula CsPbXs, wherein X is a halide selected from the group consisting of Cl , Br or I or combinations thereof , c ) tube-shaped metal salt nanoclusters wherein the metal salt is selected from lead salt , tin salt and a mixture thereof , ; wherein said upconversion nanoparticles and said perovs kite nanoparticles have a mean size of less than 20 nm, and wherein said upconversion nanoparticles and said perovs kite nanoparticles are arranged inside the tube-shaped metal salt nanoclusters .

[0179] As has been explained above , the hybrid material of the present invention exhibit advantageous properties , and can yield higher efficiency with better stability, in particular the hybrid material films , when implemented in photovoltaic devices .

[0180] Therefore , the present invention further relates to the use of the hybrid material or the film as defined above in the photovoltaic industry .

[0181] In a particular embodiment , the hybrid material or the film of the present invention can be used in photovoltaic devices , preferably in perovs kite based solar cells . In a preferred embodiment , the hybrid material or the film of the present invention can be used as an active layer material in perovs kite solar cells ; hybrid solar cell-batteries , and other such devices including an active layer comprising a perovs kite material disposed between two electrodes .

[0182] Examples

[0183] The present invention is further illustrated by the following examples , which are not to be construed in any way as imposing limitations upon the scope thereof .

[0184] Example 1 : Inorganic halide perovskite nanoparticles synthesis (CsPbBrs )

[0185] In a three-neck flas k, a mixture of 407 mg of CS2CO3 , 1 . 25 mL of oleic acid and 20 mL of octadecene (ODE ) was heated at 120 °C for one hour under vacuum and continuous stirring . After that time , vacuum was changed into nitrogen and the temperature was increased up to 150 ° C for

[0186] 30 minutes to obtain cesium oleate . In another three-neck flask, PbBr2 (345 mg) , octadecene (ODE) 25 mL, 2.5 mL of oleic acid and 2.5 mL of oleyl amine were added. The reaction mixture was heated under vacuum at 120 °C for one hour. Afterwards, the mixture was heated to 180 °C and the vacuum was changed into argon. At 180 °C, the cesium oleate solution previously obtained was injected. Immediately, the solution was cooled to room temperature in a water-ice bath. The nanoparticles obtained were purified by centrifugation with toluene (2500 rpm, 5 minutes, 15 °C) .

[0187] Example 2: Synthesis of upconversion nanoparticles (NaYF4 / Yb3+, Tm3+, Gd3+) In a round bottom flask, a mixture of 15 mL of octadecene (ODE) and 8 mL of oleic acid was provided. Then, YC13 ’6H2O (135.8 mg) YbC13 ’6H2O, (96.9 mg) , GdC13 ’6H2O, (111.5 mg) and TmC13 ’6H2O, (1.15 mg) were added.

[0188] The mixture was heated at 160 °C in a round bottom flask under continuous stirring and a N2 atmosphere. After dissolution of the lanthanide salts, the mixture was cooled down to 60 °C and 10 mL of a solution of methanol containing NaOH (100 mg / mL) and NH4F (148.2 mg / mL) were then slowly added. The mixture was stirred at 60 °C for 30 minutes, and then heated up at 120 °C to remove MeOH . Finally, the mixture was heated at 320°C (ca. 8 °C / min) for 15 minutes. The solution was then allowed to cool to room temperature and the nanoparticles precipitated by means of centrif ugation / redispersion cycles at 10000 rpm, 2 minutes, 22 °C. Finally, the UPNCs were redispersed in cyclohexane.

[0189] Example 3 : Synthesis of PbSCA tube-shaped nanoclusters

[0190] Preparation of lead (II) oleate

[0191] A solution of lead oleate was prepared according to a method previously described (X. Zhang, L. Lv, L. Ji, G. Guo, L. Liu, D. Han, B. Wang, Y. Tu, J. Hu, D. Yang, A. Dong, J. Am. Chem. Soo. , 2016, 138, 3290) .

[0192] Preparation of PbSCu tube-shaped nanoclusters

[0193] Then, PbSCA nanoclusters were prepared by mixing in 10 mL of chloroform lead oleate (0.0375 mmol) , cyclohexane methylammonium hydrogen sulphate (0.0375 mmol) and oleic acid (0.6 mL, 1.7 mmol) followed by stirring. After obtaining a clear solution, the mixture is precipitated by addition of ethanol (30 mL) followed by centrifugation (10000 rpm, 5 minutes, 15 °C) . The residue of nanoclusters was dispersed in 3 mL of hexane. The dispersion was incubated for 1 day, followed by centrifugation (2500 rpm, 5 minutes, 15 °C) . Then, the supernatant including tube-shaped nanoclusters was collected and the residue of tubeshaped nanoclusters was dispersed in hexane.

[0194] Example 4: Synthesis of SnSO4 tube-shaped nanoclusters Preparation of tin (II) oleate

[0195] In a glove box, a solution of tin oleate was prepared by mixing in a three-neck flask tin(II) acetate (59.6 mg, 0.252 mmol) , oleic acid (1 mL) and oleyl amine (9 mL) . The mixture was heated during an hour at 150 °C under continuous stirring and a N2 atmosphere. After that time, the reaction mixture is cooled down to room temperature and the tin (II) oleate was kept in a glove box.

[0196] Preparation of SnSCf tube-shaped nanoclusters

[0197] Then, SnSCA nanoclusters were prepared by mixing in 10 mL of chloroform tin oleate (0.0375 mmol) , cyclohexane methylammonium hydrogen sulphate (0.052 mmol for tin) and oleic acid (0.8 mL, 2.26 mmol) followed by stirring. After obtaining a clear solution, the mixture is precipitated by addition of ethanol (30 mL) followed by centrifugation (10000 rpm, 5 minutes, 15 °C) . The residue of nanoclusters was dispersed in 3 mL of hexane. The dispersion was incubated for 3 days , followed by centrifugation (2500 rpm, 5 minutes, 15 °C) . Then, the supernatant including tube-shaped nanoclusters was collected and the residue of tubeshaped nanoclusters was dispersed in hexane.

[0198] Example 5 : Synthesis of the hybrid material

[0199] The hybrid material was assembled by mixing a suspension of perovskite nanoparticles, a suspension of upconversion nanoparticles and a suspension of lead tube-shaped nanoclusters in hexane at a 5:1:1 under stirring and the resulting suspension was incubated for a period of 24 hours. After incubation, the hybrid material was isolated by centrifugation (7000 rpm, 5 minutes, 15 °C) and redispersed in hexane.

[0200] The arrangement of the perovskite and upconversion nanoparticles within the PbSCA nanoclusters in the hybrid material can be seen in the TEM image of Figure 1.

[0201] Example 6: Preparation of the hybrid material film A suspension containing the hybrid material in hexane was deposited on a glass substrate, at 800 rpm for 60 seconds. This process is repeated. The film of material was kept under vacuum for one hour.

[0202] The morphology of the film surface is shown in the SEM micrograph of Figure 2. It can be observed that the film was uniform on the entire surface without any cracks and voids. Further, the film obtained exhibited a bright green emission under UV light as shown in Figure 3.

[0203] Example 7. Film degradation experiments

[0204] The degradation analysis of the thin films of hybrid material is conducted according to International Summit on Organic Photovoltaic Stability (ISOS) protocols. The protocols performed were: dark storage, high temperature, damp heat and light soaking experiments. The most common stress agents used in the aforementioned degradation experiments are ambient air, temperature, humidity and light. a) Dark storage experiment:

[0205] The temperature used in the dark storage experiment was 2112 °C with a relative humidity of 4515%, conducted in laboratory atmosphere from 2 to 181 hours. After that time, the films of hybrid material still had a greenish emission, and the transmission of the lead halide perovskite nanoparticle decreased from 88.3% to 81.1%, as shown in Figure 4. b) High temperature experiment:

[0206] The temperature used in this experiment was 85 °C with a relative humidity of 1015% in an oven from 2 to 163 hours. The films of hybrid materials lost their greenish emission at the end of the experiment, although the coating was still present. The transmission of the lead halide perovskite decreased from 92.5% to 68%. c) Damp heat experiment:

[0207] The damp heat experiment was conducted at 85 °C with a relative humidity of 85% in a climatic chamber from 2 to 181 hours. At the end of the experiment, the coating was almost degraded and the transmission of the lead halide perovskite decreased from 89.3% to 73.2%. d) Light soaking experiment:

[0208] The light soaking experiment was performed under 1 sun irradiation of solar simulator at 2512 °C with a relative humidity of 4515% from 2 to 72 hours. At the end of the experiment, there was no greenish emission from the films of hybrid material, and the transmission of the lead halide perovskite decreased from 95.6% to 78.3% .

Claims

CLAIMS1 . A hybrid material comprising : a . upconversion nanoparticles of formula MLnF4 : RE+3, wherein M is an alkaline metal , Ln is a lanthanide element or an element located within group 3 of the periodic table and chemically similar to a lanthanide element and RE+3is an ion of rare earth elements or combinations thereof , b . inorganic halide perovs kite nanoparticles of formula CsPbXs , wherein X is an halide selected from the group consisting of Cl , Br or I or combinations thereof , c . tube-shaped metal salt nanoclusters , wherein the metal salt is selected from lead salt , tin salt and a mixture thereof ; wherein said upconversion nanoparticles and said perovs kite nanoparticles have a mean size of less than 20 nm, and wherein said upconversion nanoparticles and said perovs kite nanoparticles are arranged inside the tube-shaped metal salt nanoclusters .2 . The hybrid material according to claim 1 , wherein the tube- shaped nanoclusters are lead salt nanoclusters .3 . The hybrid material according to any of claim 1 or 2 , wherein the lead salt of the tube-shaped nanoclusters is lead sulphate .4 . The hybrid material according to claim 1 , wherein the tubeshaped nanoclusters comprise a mixture of a lead salt and a tin salt .5 . The hybrid material according to any of claims 1 to 4 , wherein the tube-shaped nanoclusters comprise a 50-100 wt% , preferably a 60-100 wt% , of a metal salt with respect to the total weight of the nanoclusters .6 . The hybrid material according to claim 1 , wherein the tubeshaped nanoclusters are tin salt nanoclusters .

7. The hybrid material according to claim 6, wherein the tin salt of the tub-shaped nanoclusters is tin sulphate.

8. The hybrid material according to any of claims 1 to 7 , wherein the upconversion nanoparticles and / or the perovskite nanoparticles have a mean size between 5 nm and 15 nm, preferably between 9 and 10 nm.

9. The hybrid material according to any of claims 1 to 8 , wherein the tube-shaped metal salt nanoclusters have a mean diameter between 15 and 25 nm.

10. The hybrid material according to any one of claims 1 to 9, wherein the upconversion nanoparticles and the perovskite nanoparticles are assembled forming linear chains along the length of the tube-shaped metal salt nanocluster.

11. The hybrid material according to any one of claims 1 to 10, wherein the ratio of upconversion nanoparticles : perovskite nanoparticles : tube-shaped metal salt nanoclusters is between 1:3:1 and 1:7:1, preferably about 1:5:1.

12. The hybrid material according to any one of claims 1 to 11, wherein the upconversion nanoparticles have the formula NaYF4: Yb3+, Er3+, NaYF4: Yb3+, Tm3+, NaYF4: Yb3+, Ho3+orNaYF4: Yb3+, Gd3+, Tm3+.

13. The hybrid material according to any one of claims 1 to 12, wherein the perovskite particles have the formula CsPbBrs.

14. A film comprising the hybrid material according to any one of claims 1 to 13, preferably obtained by spin coating.

15. The film according to claim 14, wherein the thickness of the film is between 200 and 350 nm.

16. A method for preparing the hybrid material according to any claims 1 to 13, comprising the steps of: a. providing a lead precursor solution at a temperature of 50- 350 °C under an inert atmosphere, b. injecting a cesium precursor into the solution of step (a) under an inert atmosphere and quenching the resulting mixture to obtain a suspension of inorganic perovskite nanoparticles of formula CsPbXs, wherein X is an halide selected from Cl, Br or I or combinations thereof, having a mean size of less than 20 nm, c. providing a solution containing a precursor of nanoparticles of formula MLnF4 : RE+3, wherein M is an alkaline metal, Ln is a lanthanide element or an element located within group 3 of the periodic table and chemically similar to a lanthanide element and RE+3is an ion of rare earth elements or combinations thereof in a solvent; d. subjecting the solution of step (c) to thermal decomposition to obtain a suspension of upconversion nanoparticles having a mean size of less than 20 nm; e. providing a metal salt nanocluster precursor solution in a first solvent, wherein the metal salt is selected from lead salt, tin salt and a mixture thereof; adding a second solvent, precipitating the metal salt nanoclusters and adding said precipitate to a third solvent to perform an incubation to yield tube-shaped metal salt nanoclusters; f. mixing the perovskite nanoparticles of step (b) , the upconversion nanoparticles of step (d) and the tube-shaped metal salt nanoclusters of step (e) , incubating the resulting mixture; and subjecting said mixture to centrifugation to isolate the hybrid material .

17. The method according to claim 16, wherein the tube-shaped metal salt nanocluster precursor solution of step (e) is incubated for a period of at least 20 hours, preferably for a period between 24 h and 72 h.

18. The method according to claim 16 or 17, wherein the weight ratio of the perovskite nanoparticles : upconversion nanoparticles : tube-shaped metal salt nanoclusters in the resulting mixture of step (f) ranges between 3:1:1 and 7:1:1, preferably is about 5:1:

119. The method according to claims 15 to 18, wherein the metal salt of the nanocluster precursor is a lead salt.

20. The method according to claim 19, wherein the nanocluster precursor is a lead sulphate nanocluster precursor comprising lead oleate and cyclohexane methylammonium hydrogen sulphate (CHMAHS) .

21. The method according to claims 15 to 18 wherein the metal salt of the nanocluster precursor is a tin salt.

22. The method according to claim 21 wherein the nanocluster precursor is a tin sulphate nanocluster precursor comprising tin oleate and cyclohexane methylammonium hydrogen sulphate (CHMAHS) .

23. The method according to claims 16 to 22, wherein the mixture of step (f) is incubated for a period of 12 to 36 h, preferably for a period of about 24 h24. Use of the hybrid material according to any one of claims 1-13, or the film according to any one of claims 14-15 in the photovoltaic industry.

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