Structure, method for producing a structure and optoelectronic device

Abstract

A structure is provided, the structure comprising: - a cluster of nanoparticles, each nanoparticle configured to convert electromagnetic radiation of a first wavelength range into electromagnetic radiation of a second wavelength range, and - an encapsulation at least partially surrounding the cluster of nanoparticles and comprising a metal oxide. Further, a method for producing a structure and an optoelectronic device are provided.

Description

[0001] 2024PF00852 October 28, 2025

[0002] P2024, 0745 WO N - 1 -

[0003] Description

[0004] STRUCTURE, METHOD FOR PRODUCING A STRUCTURE AND OPTOELECTRONIC DEVICE

[0005] A structure, a method for producing a structure and an optoelectronic device are specified.

[0006] It is an obj ect to provide a structure with improved stability. It as a further obj ect to provide a method for producing a structure with improved stability.

[0007] A structure is provided. A structure may comprise several distinguishable parts or components .

[0008] According to at least one embodiment, the structure comprises a cluster of nanoparticles . A cluster is to be understood as a quantity of components, as for example a quantity of nanoparticles, that can be regarded as a unitary ensemble . The nanoparticles that form the cluster can be linked to each other by chemical bonds or chemical interactions to form the cluster, or they can be held together by external forces .

[0009] A nanoparticle can be a semiconductor nanoparticle, in particular a quantum dot (QD) . Further, a nanoparticle can have a size in the nanometer range, for example between and including 1 nm and 100 nm. Due to their size, nanoparticles can have different properties than a bulk material formed from the same material . For example, nanoparticles can be intended to have properties of a phosphor, i . e . of a conversion material . 2024PF00852 October 28, 2025

[0010] P2024, 0745 WO N 2

[0011] According to at least one embodiment, each nanoparticle is configured to convert electromagnetic radiation of a first wavelength range (also : primary radiation) into electromagnetic radiation of a second wavelength range (also : secondary radiation) . In particular, the nanoparticles absorb the electromagnetic radiation of the first wavelength range, convert the electromagnetic radiation of the first wavelength range into electromagnetic radiation of the second wavelength range and emit electromagnetic radiation of the second wavelength range . Depending on the composition of the material of the nanoparticles and of their size, the primary radiation may be in the UV and / or visible range of electromagnetic radiation, and the secondary radiation may be in the range of visible or IR of electromagnetic radiation. In particular, the nanoparticles can be used in many applications, such as in light-emitting diodes (LEDs) . In LEDs such nanoparticles can have the function of downconverters, i . e . the primary radiation is converted into a secondary radiation which comprises longer wavelengths than the primary radiation.

[0012] According to at least one embodiment, the structure further comprises an encapsulation. An encapsulation is understood to be a layer or shell being applied on the outer surface of the cluster of nanoparticles . Thus, it can be in mechanical contact to the outer surface of the cluster or to any other layer that is applied on the outer surface of the cluster of nanoparticles . In other words, the encapsulation is at the most in mechanical contact to parts of the outer surface of nanoparticles that form the outer surface of the cluster, but it is not in mechanical contact to all nanoparticles of the cluster . 2024PF00852 October 28, 2025

[0013] P2024, 0745 WO N 3

[0014] According to at least one embodiment, the encapsulation at least partially surrounds the cluster of nanoparticles . In particular, the encapsulation fully surrounds the cluster of nanoparticles . In this case, it forms a complete layer or shell around the cluster of nanoparticles .

[0015] According to at least one embodiment, the encapsulation comprises a metal oxide . In particular, the encapsulation consists of a metal oxide . Exemplary metals that can be part of the metal oxide are silicon, aluminum, zinc, titanium, and hafnium.

[0016] According to at least one embodiment, a structure is provided, the structure comprising:

[0017] - a cluster of nanoparticles, each nanoparticle configured to convert electromagnetic radiation of a first wavelength range into electromagnetic radiation of a second wavelength range, and

[0018] - an encapsulation at least partially surrounding the cluster of nanoparticles and comprising a metal oxide .

[0019] Quantum dots, in particular quantum dots that are free of Cadmium, are suitable downconverters in various lighting applications like LEDs . However, they are not sturdy enough to be used in, for example, lighting applications without protecting them from ambient conditions . In particular, they need to be protected from oxygen and water which is normally present in ambient conditions . Stability under operating conditions is a widespread problem to be solved. Some conventional methods for protection are only applicable for Cadmium-based quantum dots . 2024PF00852 October 28, 2025

[0020] P2024, 0745 WO N 4

[0021] The structure as described here combines the formation of a cluster of nanoparticles with an encapsulation containing a metal oxide . By this, nanoparticles, in particular quantum dots, are further protected and a material with superior reliability under illumination in ambient conditions is provided. Thus, the nanoparticles have an improved stability and photoluminescent quantum yield (PLQY) under illumination, for example, under blue-light illumination. Nanoparticles with improved stability lead to an improved maintenance of efficiency, color point, and other metrics of a device that implements the structure, for example an optoelectronic device like a light emitting diode (LED) .

[0022] The formation of clusters of nanoparticles provides already a natural barrier to ambient species like oxygen and water . For example, if the nanoparticles comprise any ligands at their outer surface, the ligands can form a barrier . If there are, for example hydrophobic ligands, they can prevent the access of hydrophilic species into the cluster . Additionally, a cluster which is much larger than a single nanoparticle, reduces the surface area that is exposed to the ambient environment . While a single nanoparticle has a large surfacearea to volume ratio, a cluster of nanoparticles has a smaller surface area to volume ratio, as the surface area increases more slowly than the volume as the radius of a spherical particle increases . Thus, the surface area of the cluster that is affected by ambient conditions is reduced with respect to the volume of the cluster in comparison to a single nanoparticle .

[0023] Therefore, when combining a cluster of nanoparticles with a metal oxide encapsulation, also nanoparticles, in particular quantum dots, may be used for the structure, that are 2024PF00852 October 28, 2025

[0024] P2024, 0745 WO N 5

[0025] normally otherwise sensitive to or not compatible with metal oxide encapsulation strategies .

[0026] An encapsulation of metal oxides provides an additional barrier to chemical species that would degrade nanoparticles, in particular quantum dots . Furthermore, metal oxides comprise different properties as barrier than hydrocarbons that are, for example, present in ligands of the nanoparticles . Therefore, the additional encapsulation of metal oxide provides an additional and complementary protection for the nanoparticles .

[0027] Thus, the combination of a cluster of nanoparticles and an encapsulation of metal oxide leads to an improved reliability of the resulting structure .

[0028] According to at least one embodiment, the cluster of nanoparticles comprises a size in the range of 10 nm to 10 pm inclusive . The size in this context is equal to the diameter of the cluster . Thus, large clusters of nanoparticles are provided, which can provide a significant diffusion barrier due to their sheer size .

[0029] According to at least one embodiment, the nanoparticles comprise a Cd-free compound semiconductor material . In particular, the nanoparticles consist of a Cd-free compound semiconductor material . Thus, the nanoparticles do not include any Cd. For example, the compound semiconductor material is chosen from II-VI compound semiconductor materials, III-V compound semiconductor materials, I-III-VI compound semiconductor materials, and combinations thereof such as II-III-V compound semiconductor materials . A III-V compound semiconductor material comprises at least one 2024PF00852 October 28, 2025

[0030] P2024, 0745 WO N - 6 -

[0031] element of group 13 of the periodic table, for example B, Al, Ga, In, and at least one element of group 15 of the periodic table, for example N, P, As . An II-VI compound semiconductor material comprises at least one element of group 2 or 12 (except Cd) of the periodic table, for example Zn or Mg, and at least one element of group 16 of the periodic table, for example 0, S, Se, Te . An I-III-VI semiconductor compound material comprises at least one element of group 11 of the periodic table, for example Ag, at least one element of group 13 of the periodic table, for example B, Al, Ga, In, and at least one element of group 16 of the periodic table, for example 0, S, Se, Te . Accordingly, an II-III-V compound semiconductor material comprises at least one element of group 2 or 12 (except Cd) of the periodic table, at least one element of group 13 of the periodic table and at least one element of group 15 of the periodic table . For instance, the nanoparticle comprises or consists of a sulfide, a selenide, a nitride or a phosphide . Exemplary compound semiconductor materials of the nanoparticles are InP and ZnS . In particular quantum dots may comprise a core shell structure . This means, they comprise a core of a first compound semiconductor material and at least one shell of a different, second compound semiconductor material . For example, a quantum dot comprises an InP core and one or more shells comprising two or more of Zn, Se and S . A further example is a quantum dot comprising an AglnGaS core and at least one shell of AgGaS .

[0032] According to at least one embodiment, the encapsulation comprises a thickness in the range of 1 nm to 500 nm inclusive . The thickness of the encapsulation can be chosen in this size range and, thus, the thickness of the encapsulation can be tuned in dependence of the intended application of the structure and the nature of the 2024PF00852 October 28, 2025

[0033] P2024, 0745 WO N - 7 -

[0034] nanoparticles that form the cluster and that are to be encapsulated by the encapsulation.

[0035] According to at least one embodiment, the metal oxide of the encapsulation is chosen from silica, alumino-silicate, zincsilicate, alumina, titania, hafnia and combinations thereof . In particular, the metal oxide is chosen from silica, alumino-silicate, zinc-silicate and combinations thereof . Thus, the expression "metal oxide" also comprises mixed metal oxides such as alumino-silicate . For example, the metal oxide is silica . These materials, in particular silica, provide good barrier properties and can be easily grown on the cluster of nanoparticles .

[0036] According to at least one embodiment, the structure further comprises at least one additive within the cluster . "Within" means, that the additive is incorporated in the cluster and, thus, also encapsulated by the encapsulation. Additives can be chosen from beneficial molecules that further slow down or halt degradation of nanoparticles and, thus, enhance their lifetime . Such molecules act, for example, as antioxidants, or crosslinkers . Accordingly, the at least one additive can be embedded in the cluster, or it can be chemically bound to the nanoparticles, and / or to ligands on the surface of the nanoparticles .

[0037] According to at least one embodiment, the additive is chosen from pentaerythritol tetrakis ( 3-mercaptopropionate ) , betamercaptoethanol, and combinations thereof . Pentaerythritol tetrakis ( 3-mercaptopropionate ) can act as a crosslinker for ligands being present on the surface of the nanoparticles and stabilize the ligands on the nanoparticles inside the cluster . Alternatively or additionally, pentaerythritol 2024PF00852 October 28, 2025

[0038] P2024, 0745 WO N 8

[0039] tetrakis ( 3-mercaptopropionate ) can act as a ligand for the nanoparticles, in particular, for the quantum dots, and passivate the surfaces of the nanoparticles . Alternatively or additionally, pentaerythritol tetrakis ( 3-mercaptopropionate ) can act as a crosslinker, binding the nanoparticles together and adding thus stability to the cluster . Betamercaptoethanol (BME) can act, for example, as a reducing agent stabilizing the cluster with regard to oxidative stress .

[0040] According to at least one embodiment, a ratio of an amount of additive to an amount of nanoparticles in the cluster of nanoparticles is in a range of 1 : 100 to 100 : 1. With such a ratio, there are enough additives to act as crosslinker for ligands on the nanoparticles, as ligand for nanoparticles, as a crosslinker for the nanoparticles, and / or as reducing agent . For example, the ratio of an amount of additive to an amount of nanoparticles is in a range of 1 : 100 to 1 : 1 for additives with antioxidant properties, such as BME . As a further example, the ratio of an amount of additive to an amount of nanoparticles is in a range of 1 : 1 to 100 : 1 for an additive with crosslinking properties, such as pentaerythritol tetrakis ( 3-mercaptopropionate ) .

[0041] According to at least one embodiment, the nanoparticles comprise ligands . In particular, the ligands are present on the surface of the nanoparticles . They can have, for example, hydrophobic properties . The ligands are, in particular, native ligands, i . e . the same ligands as ligands being present on single nanoparticles, i . e . nanoparticles that are not part of the encapsulated cluster of nanoparticles . Native ligands can be chosen, for example, from thiols, e . g. ,

[0042] 1-dodecanethiol , carboxylates, e . g. , oleic acid / oleate, and 2024PF00852 October 28, 2025

[0043] P2024, 0745 WO N 9

[0044] amines, e . g. oleylamine . In other words, a cluster of nanoparticles can be formed, and the encapsulation can be grown on the cluster of nanoparticles without inducing a ligand exchange on the surface of the nanoparticles . The lack of a ligand exchange allows for a better size control of the clusters and an improved, low size distribution of the clusters and of the structure . Moreover, any disadvantageous effect of a ligand exchange can be avoided, if no ligand exchange takes place . Thus, by applying an encapsulation as described here, i . e . without a ligand exchange, leads to nanoparticles with improved brightness and stability.

[0045] According to at least one embodiment, the structure further comprises a layer of surfactant between the cluster of nanoparticles and the encapsulation. Thus, the layer of surfactant surrounds the cluster of nanoparticles and is itself at least partially surrounded by the encapsulation. In this embodiment, the layer of surfactant has a common boundary with the outer surface of the cluster of nanoparticles and a common boundary with the inner surface of the encapsulation, i . e . , the surface of the encapsulation facing the cluster of nanoparticles .

[0046] A surfactant is to be understood as a molecule having a hydrophobic and a hydrophilic end. Due to this chemical composition, a surfactant helps to form dispersions or emulsions of substances that are without a surfactant non-miscible, like, for example oil-in-water emulsions . The presence of a surfactant may stabilize the cluster of nanoparticles and, thus, also the structure .

[0047] According to at least one embodiment, the surfactant is chosen from nonionic, cationic, and / or anionic surfactants . 2024PF00852 October 28, 2025

[0048] P2024, 0745 WO N - 10 -

[0049] In particular, the surfactant is chosen from at least one of octylphenoxypolyethoxyethanol ( Igepal) , cetyltrimethylammoniumbromid (CTAB) , and sodium dodecyl sulfate (SDS) .

[0050] Furthermore, a method for producing a structure is specified. In particular, a method for producing the structure as disclosed here is specified. Thus, embodiments, features, and advantages described in combination with the structure also apply to the method and vice versa .

[0051] According to at least one embodiment, the method for producing a structure comprises :

[0052] - providing nanoparticles, the nanoparticles being configured to convert electromagnetic radiation of a first wavelength range into an electromagnetic radiation of a second wavelength range

[0053] - forming a cluster of nanoparticles, and

[0054] - forming an encapsulation at least partially encapsulating the cluster of nanoparticles, the encapsulation comprising a metal oxide .

[0055] In the step of providing nanoparticles, quantum dots are provided, for instance . According to at least one embodiment, the nanoparticles comprise a Cd-free compound semiconductor material . For example, the material of the nanoparticles is chosen from II-VI compound semiconductor materials, III-V compound semiconductor materials, and combinations thereof such as II-III-V compound semiconductor materials .

[0056] In the step of forming an encapsulation at least partially encapsulating the cluster of nanoparticles, the encapsulation comprising a metal oxide, the structure is formed. The metal 2024PF00852 October 28, 2025

[0057] P2024, 0745 WO N 11

[0058] oxide is chosen, for example, from silica, alumino-silicate, zinc-silicate, alumina, titania, hafnia and combinations thereof .

[0059] According to at least one embodiment, forming the cluster of nanoparticles includes the steps of

[0060] - mixing the nanoparticles with a first solvent, a surfactant and a second solvent, wherein the first solvent and the second solvent are not miscible,

[0061] - forming an emulsion from the mixture, and

[0062] - removing the first solvent .

[0063] The first solvent and the second solvent being not miscible is to be understood that they have no or only a low solubility in each other .

[0064] According to a first alternative, the first solvent is chosen from non-polar solvents, for example cyclohexane, and the second solvent is water . Accordingly, in the step of forming an emulsion from the mixture, an oil-in-water emulsion is formed. For example, cyclohexane, water and SDS as a surfactant are mixed with the nanoparticles .

[0065] According to a second alternative, the first solvent is chosen from non-polar solvents, for example octane, and the second solvent is chosen from polar solvents, for example DMF. Accordingly, in the step of forming an emulsion from the mixture, an oil-in-polar emulsion is formed. For example, octane, DMF, and Igepal as a surfactant are mixed with the nanoparticles .

[0066] According to a third alternative, the first solvent is chosen from hydrocarbons, for example cyclohexane, and the second 2024PF00852 October 28, 2025

[0067] P2024, 0745 WO N 12

[0068] solvent is chosen from perfluorinated hydrocarbons .

[0069] Accordingly, in the step of forming an emulsion from the mixture, an oil-in-perf luoro oil emulsion is formed. For example, cyclohexane, perfluorohydrocarbon and a partially fluorinated block-copolymer as a surfactant are mixed with the nanoparticles . The fluorinated part of the partially fluorinated block-copolymer may interact with the continuous fluorinated phase . The non-f luorinated part of the partially fluorinated block-copolymer (i . e . the part with C-H bonds instead of C-F bonds) may interact with the discontinuous phase containing the nanoparticles . The partially fluorinated block-co-polymer may thus be situated at the interfaces and stabilizes the emulsion.

[0070] According to at least one embodiment, the surfactant is chosen from nonionic, cationic, and / or anionic surfactants . In particular, the surfactant is chosen from at least one of octylphenoxypolyethoxyethanol ( Igepal) , cetyltrimethylammoniumbromid (CTAB) , sodium dodecyl sulfate (SDS) , and partially fluorinated block-co-polymer .

[0071] According to at least one embodiment, the step of forming an emulsion from the mixture is carried out by stirring or with the aid of a sonicator . In this step, droplets are formed, wherein a droplet is stabilized by the surfactant and comprises, inside of the surfactant molecules, the nanoparticles being dispersed in the first solvent . The surfactant forms the outer surface of a droplet . Furthermore, the surfactant stabilized droplets are present in a continuous phase of water or of the second solvent, respectively. Thus, the oil-in-water emulsion, or the oil-inpolar emulsion, or the oil-in-perf luoro oil emulsion are 2024PF00852 October 28, 2025

[0072] P2024, 0745 WO N - 13 -

[0073] formed. Due to the surfactant, the nanoparticles cannot escape from the droplets and, additionally, the droplets do not coalesce .

[0074] According to at least one embodiment, removing the first solvent includes drying out the first solvent, exchanging the first solvent by another solvent, adding another surfactant, and combinations thereof . Drying out the first solvent is carried out by raising the temperature, for example . The first solvent exits the droplets and clusters of nanoparticles that are covered and stabilized by the surfactant remains, wherein the clusters are dispersed in the water or in the second solvent, respectively. When a different surfactant is added, the first solvent can move to droplets that are formed by the different surfactant but do not contain any nanoparticles . According to at least one embodiment, the step of removing the first solvent is carried out for a time chosen from several minutes to several hours .

[0075] According to at least one embodiment, forming an encapsulation at least partially encapsulating the cluster of nanoparticles is performed by growing an encapsulation comprising a metal oxide on the cluster of nanoparticles . According to at least one embodiment, the encapsulation, i . e . the layer or shell of metal oxide, is grown by a catalyst based method. In particular, a coordination-complex is used as a catalyst . A coordination-complex can comprise a metal and at least one ligand. For example, the metal is selected from the following group : alkali metal, alkaline earth metal, transition metal or post-transition metal . The ligand is for example chosen from the group consisting of : alkoxide, acetylacetonate (acac) , ammine, diketone, hybride, hydrate, ethylacetoacetate, acetylacetonate derivatives and 2024PF00852 October 28, 2025

[0076] P2024, 0745 WO N - 14 -

[0077] combinations thereof . In this method, precursors of the desired metal oxides and the catalyst are added to the oil-in-water emulsion, the oil-in-polar emulsion, or to the oil-in-perfluoro oil emulsion, and the encapsulation material is directly formed on the cluster or on the surfactant .

[0078] Precursors of the metal oxide can be chosen from a group consisting of tetraethyl orthosilicate, tetramethyl orthosilicate, tetrabutyl orthosilicate, tetrapropyl orthosilicate, a silane with an amino, mercapto, phosphonic, isocyanate, aldehyde, or carboxylic headgroup and combinations thereof . For example, tetraethyl orthosilicate (TEOS) is used as a metal oxide precursor, and an aluminum complex is used as a coordination-complex . During growing the encapsulation, the coordination-complex can hydrolyse and form the encapsulation. Thus, the coordination-complex can act as a catalyst, a metal source, and as both. This method allows for a controlled formation of the encapsulation and its thickness can be adjusted as desired. As the clusters of nanoparticles are stabilized by the surfactants, for example, no ligand exchange of ligands being present on the nanoparticles takes place during the formation of the encapsulation .

[0079] According to at least one embodiment, at least one additive is added to the cluster of nanoparticles before or after forming the cluster of nanoparticles . According to at least one embodiment, the additive is chosen from pentaerythritol tetrakis ( 3-mercaptopropionate ) , beta-mercaptoethanol (BME) , and combinations thereof . For example, BME as a stabilizing agent can be added to the mixture before or after forming the cluster of nanoparticles . Even if the cluster of nanoparticles is already formed, BME is able to penetrate through the layer of surfactants and to disperse within the 2024PF00852 October 28, 2025

[0080] P2024, 0745 WO N 15

[0081] cluster of nanoparticles . Tetrakis ( 3-mercaptopropionate ) which may act as a crosslinking additive or as an additive for forming ligands on the nanoparticles, on the other hand, can be added to the mixture before forming a cluster of nanoparticles and initiate and / or enhance the crosslinking chemistry between the nanoparticles or their ligands or it can form ligands on the nanoparticles during the formation of the cluster of nanoparticles .

[0082] According to at least one embodiment, the surfactant is removed after forming the cluster of nanoparticles or the surfactant remains, in particular in form of a layer, on the cluster of nanoparticles . In particular, the surfactant can be removed in case of crosslinked nanoparticles and / or crosslinked ligands of the nanoparticles . In this case, the surfactant can be washed away while the cluster is stabilized by the crosslinks between the nanoparticles and / or their ligands . If the surfactant is not removed, the encapsulation of the cluster is carried out on the layer of surfactant around the cluster of nanoparticles .

[0083] Furthermore, an optoelectronic device is specified. In particular, the optoelectronic device comprises at least one structure described herein. Thus, embodiments, features, and advantages described in combination with the structure and the method for producing a structure also apply to the optoelectronic device and vice versa .

[0084] According to at least one embodiment, the optoelectronic device comprises :

[0085] - a semiconductor chip configured to emit electromagnetic radiation of a first wavelength range, and 2024PF00852 October 28, 2025

[0086] P2024, 0745 WO N 16

[0087] - a conversion element comprising at least one structure, in particular a plurality of structures, as described here and being configured to convert electromagnetic radiation of the first wavelength range into electromagnetic radiation of a second wavelength range .

[0088] The optoelectronic device may be a light emitting diode (LED) and the semiconductor chip a LED chip, or the optoelectronic device may be a laser diode and the semiconductor chip a laser diode chip, for example . The semiconductor chip being configured to emit electromagnetic radiation of a first wavelength range (primary radiation) may in particular emit electromagnetic radiation with wavelengths in a range being in the ultraviolet to blue spectral range .

[0089] The conversion element on the semiconductor chip may be applied directly, with a mechanical contact on the semiconductor chip, or spaced with respect to the semiconductor chip . For example, there may be an adhesive layer between the semiconductor chip and the conversion element .

[0090] The conversion element comprises at least one structure as disclosed herein. According to an embodiment, the conversion element consists of structures as disclosed herein. According to an alternative embodiment, the at least one structure is embedded in a matrix material . A matrix material may be chosen, for example, from silicone, polysiloxane, or epoxy. In this case, the conversion element may be formed as a layer or a casting.

[0091] The conversion element converts the electromagnetic radiation of the first wavelength range (primary radiation) into 2024PF00852 October 28, 2025

[0092] P2024, 0745 WO N 17

[0093] electromagnetic radiation of the second wavelength range (secondary radiation) . In particular, the second wavelength range is at least partially different from the first wavelength range . The second wavelength range comprises wavelengths that may have a lower energy compared to wavelengths of the first wavelength range . The wavelength conversion properties of the conversion element arise from the at least one structure being present in the conversion element as the nanoparticles in the structures convert the electromagnetic radiation of the first wavelength range into electromagnetic radiation of the second wavelength range .

[0094] Due to the enhanced stability of the nanoparticles under operating conditions, the stability arising, in particular, from combining clusters of nanoparticles with an encapsulation of metal oxide, the optoelectronic device has also enhanced stability and, thus, an improved efficiency and an increased lifetime . Additionally, even under operating condition, the photoluminescence quantum yield (PLQY) of the nanoparticles in the structures is not or not significantly affected.

[0095] According to at least one embodiment, the semiconductor chip comprises or is a micro-LED (LED: light-emitting diode) .

[0096] As a broad definition, a micro-LED could be seen as any light-emitting diode with a particularly small size . MicroLEDs may comprise a width, a length, a thickness and / or a diameter smaller than or equal to 100 micrometers, in particular smaller than or equal to 70 micrometers, for example smaller than or equal to 50 micrometers . In particular, micro-LEDs, for example rectangular micro-LEDs, have an edge length, in particular in plan view of layers of 2024PF00852 October 28, 2025

[0097] P2024, 0745 WO N 18

[0098] the semiconductor layer sequence, of a radiation exit surface of smaller than or equal to 70 micrometers, for example smaller than or equal to 50 micrometers . For example, a micro-LED is a light-emitting diode with a growth substrate removed, such that a thickness of the micro-LED is in the range between and including, for example, 1.5 micrometers and 10 micrometers . For example, the micro-LED is provided on a wafer having releasable retaining structures . The micro-LED can be detached from the wafer in a non-destructive manner .

[0099] In particular, micro-LEDs are mainly used in displays . The micro-LEDs form pixels or subpixels and emit light of a defined color . Small pixel sizes and a high density with close distances make micro-LEDs suitable, among others, for small monolithic displays for augmented reality applications, especially data glasses . In addition, other applications are being developed, in particular regarding their use in data communication or pixelated lighting applications .

[0100] Advantageous embodiments and developments of the structure, the method for producing a structure, and of the optoelectronic device will become apparent from the exemplary embodiments described below in conjunction with the figures .

[0101] In the figures :

[0102] Figure 1 shows a schematic cross section of a structure according to an exemplary embodiment .

[0103] Figure 2 shows PLQY values in dependence of time of reference examples and of an exemplary embodiment . 2024PF00852 October 28, 2025

[0104] P2024, 0745 WO N - 19 -

[0105] Figure 3 shows a schematic cross section of an optoelectronic device according to an exemplary embodiment .

[0106] Figure 4 shows a schematic cross section of an optoelectronic device according to a further exemplary embodiment .

[0107] In the exemplary embodiments and figures, similar or similarly acting constituent parts are provided with the same reference signs . The elements illustrated in the figures and their size relationships among one another should not be regarded as true to scale . Rather, individual elements may be represented with an exaggerated size for the sake of better representability and / or for the sake of better understanding.

[0108] Figure 1 shows a schematic cross section of a structure 10. It comprises a plurality of nanoparticles 1. The plurality of nanoparticles 1 forms a cluster of nanoparticles 1. The cluster of nanoparticles 1 is surrounded by a layer of surfactant 3 which stabilizes the cluster of nanoparticles 1. The surfactant 3 is further surrounded by an encapsulation 2.

[0109] The nanoparticles 1 are quantum dots in this example . In particular, they are Cd-free quantum dots . For example, the quantum dots comprise a core of a first compound semiconductor material being InP and at least one shell comprising a second compound semiconductor material having two or more of Zn, Se, and S . According to another example, a quantum dot comprises a AglnGaS core and at least one shell of AgGaS . However, any other Cd-free compound semiconductor material chosen from II-VI compound semiconductor materials, III-V compound semiconductor materials, I-III-VI compound semiconductor materials, and combinations thereof such as II- 2024PF00852 October 28, 2025

[0110] P2024, 0745 WO N - 20 -

[0111] III-V compound semiconductor materials are possible as well . The nanoparticles 1 may have ligands on their outer surface that may be crosslinked with each other or not .

[0112] The layer of surfactant 3 comprises or consists of at least one of octylphenoxypolyethoxyethanol ( Igepal) , cetyltrimethylammoniumbromid (CTAB) , sodium dodecyl sulfate (SDS) , and partially fluorinated block-copolymer . The layer of surfactant 3 stabilizes the cluster of nanoparticles 1 and is in direct mechanical contact with the outer surface of the cluster of nanoparticles 1.

[0113] In case that the nanoparticles 1 and / or their ligands are crosslinked to each other, the layer of surfactant 3 could also be omitted, i . e . washed away before growing the encapsulation 2 (not shown here) .

[0114] The encapsulation 2 comprises a metal oxide, in this example silica . However, other metal oxides like, for example, alumino-silicate or Zn-silicate may be used as well as material for the encapsulation 2 .

[0115] The structure 10 is produced as described above, i . e . , by forming an emulsion from a mixture of a first solvent, a second solvent, a surfactant 3 and the nanoparticles 1, then removing the first solvent, and then growing the encapsulation 2 .

[0116] The structure 10 is produced by dissolving the nanoparticles 1 in a first solvent, emulsified in a second solvent containing a surfactant 3. The first solvent and the second solvent are not miscible . 2024PF00852 October 28, 2025

[0117] P2024, 0745 WO N - 21 -

[0118] The first solvent is for example chosen from non-polar solvents and the second solvent is water . Accordingly, an oil-in-water emulsion is formed from the mixture . For example, cyclohexane, water and SDS as a surfactant 3 are mixed with the nanoparticles 1 .

[0119] Alternatively, the first solvent is for example chosen from non-polar solvents and the second solvent is chosen from polar solvents . Accordingly, an oil-in-polar emulsion is formed from the mixture . For example, octane, DMF, and Igepal as a surfactant 3 are mixed with the nanoparticles 1 .

[0120] Alternatively, the first solvent is for example chosen from hydrocarbons and the second solvent is chosen from perfluorinated hydrocarbons . Accordingly, an oil-in-perf luoro oil emulsion is formed from the mixture . For example, cyclohexane, perfluorohydrocarbon and a partially fluorinated block-copolymer as a surfactant 3 are mixed with the nanoparticles 1 .

[0121] Forming an emulsion from the mixture is carried out by stirring or with the aid of a sonicator . In this step, droplets are formed, wherein a droplet is stabilized by the surfactant 3 and comprises, inside of the surfactant 3 molecules, the nanoparticles 1 being dispersed in the first solvent . The surfactant 3 forms the outer surface of a droplet . Furthermore, the surfactant 3 stabilized droplets are present in a continuous phase of the second solvent .

[0122] Thus, the oil-in-water emulsion, or the oil-in-polar emulsion, or the oil-in-perf luoro oil emulsion are formed. Due to the surfactant 3, the nanoparticles 1 cannot escape from the droplets and, additionally, the droplets do not coalesce . 2024PF00852 October 28, 2025

[0123] P2024, 0745 WO N 22

[0124] Then, the first solvent is removed by, for example, drying out the first solvent, exchanging the first solvent by another solvent, and / or adding another surfactant, and surfactant 3 stabilized clusters of nanoparticles 1 in the second solvent, are formed.

[0125] Drying out the first solvent is carried out by raising the temperature, for example . The first solvent exits the droplets and clusters of nanoparticles 1 that are covered and stabilized by the surfactant 3 remain, wherein the clusters are dispersed in the second solvent . When a different surfactant is added, the first solvent can move to droplets that are formed by the different surfactant but do not contain any nanoparticles 1. The step of removing the first solvent is carried out for a time chosen from several minutes to several hours .

[0126] Then, an encapsulation 2 of metal oxide, for example of silica, is grown around the clusters of nanoparticles 1.

[0127] Forming an encapsulation 2 at least partially encapsulating the cluster of nanoparticles 1 is performed by growing an encapsulation 2 comprising a metal oxide on the cluster of nanoparticles 1 by a catalyst based method. In particular, a coordination-complex is used as a catalyst . In this method, precursors of the desired metal oxides and the catalyst are added to the oil-in-water emulsion, the oil-in-polar emulsion, or to the oil-in-perf luoro oil emulsion, and the encapsulation material is directly formed on the cluster of nanoparticles 1 or on the surfactant 3. For example, tetraethyl orthosilicate (TEOS) is used as a metal oxide precursor, and an aluminum complex is used as a coordination- 2024PF00852 October 28, 2025

[0128] P2024, 0745 WO N 23

[0129] complex . But all combinations of precursors and coordinationcomplexes as mentioned above are possible as well .

[0130] During the production of the structures 10, the size of the cluster of nanoparticles 1 can be tuned within a range of 10 nm to 10 pm. The size of the cluster can be affected, for example, by the concentration of the nanoparticles 1 in the first solvent . For example, if a specific set of conditions ( first and second solvent, surfactant concentration, shear forces through e . g. , sonication, yields an emulsion with a defined droplet radius and volume, for example 3 pm and ~100 pm3, respectively. If the volume fraction of nanoparticles in the first solvent, for example the oil phase, is low, such as 0.001, then the "dried out" nanoparticle clusters will have a volume equal to 0.1 pm3and radius 0.3 pm. However, a volume fraction 10 x higher, in this case 0.01, will give a final volume of 1 pm3and radius of ~ 0. 6 pm .

[0131] The size of the nanoparticle clusters can also be affected by sonication energy and other shear forces like rapid stirring for forcing through a narrow aperture . Shear forces determine the initial droplet size which, together with the volume fraction of the nanoparticles, influence the final droplet size .

[0132] Additionally or alternatively, the thickness of the encapsulation 2 can be tuned within a range of 1 nm to

[0133] 500 nm. The thickness can be varied, for example, by changing the ratio of nanoparticles to precursors of the metal oxide of the encapsulation. Furthermore, additionally or alternatively, the composition of the metal oxide in the 2024PF00852 October 28, 2025

[0134] P2024, 0745 WO N 24

[0135] encapsulation 2 can be adapted according to the intended application .

[0136] Further additionally or alternatively, quantum dots, in particular quantum dots with ligands can be chosen, and the ligands can be varied as well . For example, ligands can be chosen from short ligands like pentane thiol, long ligands like octadecane thiol, wherein thiol can be replaced by amine, carboxylate or phosphate for both, short and long ligands . The interparticle spacing can be varied by the choice of ligands .

[0137] Finally, additionally or alternatively, additives can be added before or after the formation of clusters of nanoparticles 1 in order to stabilize the clusters towards oxidative stress and / or to mechanically stabilize the clusters via crosslinking reactions between the nanoparticles and / or the ligands of the nanoparticles and / or in order to form ligands on the nanoparticles 1.

[0138] For example, the additive BME is added in an exemplary embodiment of the method for production of a structure 10 in order to improve the reliability of the structure .

[0139] In a further exemplary embodiment of the method for production of the structure 10, the additive

[0140] tetrakis ( 3-mercaptopropionate ) is added before forming the cluster of nanoparticles 1, which is both a ligand for the nanoparticles 1 and a crosslinker thereby imparting additional stability of the nanoparticles 1, i . e . the quantum dots . 2024PF00852 October 28, 2025

[0141] P2024, 0745 WO N 25

[0142] In an exemplary embodiment of the method for production of structure 10, the total size of the structure 10 can be tuned to make it a drop-in replacement for traditional phosphors . This makes it easy to replace traditional phosphors in any application by the structures 10 as disclosed here .

[0143] Figure 2 shows measurements of the PLQY (photoluminescence quantum yield) in dependence of time of two reference examples of quantum dots and one exemplary embodiment of a structure 10. The measurement has been carried out in oxygen atmosphere and with blue light for exciting the respective quantum dots . Under these conditions, conventional systems show accelerated aging.

[0144] The circles show the values of non-clustered quantum dots . The quantum dots are I I I-V-quantum dot comprising Inp / ZnSeS / ZnS . It can be seen that the quantum yield significantly decreases almost immediately. The squares show the values for conventional quantum dot clusters of InP / ZnSeS / ZnS nanoparticles with a silica encapsulation produced by a conventional Stober method. Even here, PLQY decreases fast . In contrast, the crosses show the values for a structure 10 as described here, comprising InP / ZnSeS / ZnS clusters with a silica encapsulation produced as described here . The PLQY increases initially and is stable over time and prove their high reliability.

[0145] Figure 3 shows a schematic cross section of an optoelectronic device 100 according to an exemplary embodiment . The optoelectronic device 100 comprises a semiconductor chip 20 being for example an LED or micro-LED. The semiconductor chip 20 comprises an epitaxial semiconductor layer sequence with an active layer . The semiconductor chip 20 is configured to 2024PF00852 October 28, 2025

[0146] P2024, 0745 WO N - 26 -

[0147] generate electromagnetic radiation of a first wavelength range in the active layer, which exits the semiconductor chip 20 via a radiation exit surface . The first wavelength range comprises for example UV- or blue light .

[0148] A conversion element 30 is arranged on the semiconductor chip 20, in particular, on the radiation exit surface of the semiconductor chip 20. The conversion element 30 comprises or consists of structures 10 as explained with respect to figure 1. The structures 10 can be embedded in a matrix material like shown in Figure 3, or the conversion element 30 is free of a matrix material and consists of the structures 10 (shown in Figure 4 ) . In this example, the conversion element 30 is arranged directly on the semiconductor chip 20, that is without an adhesive layer arranged in between. The structures 10, in particular the nanoparticles 1 in the structures 10, convert the electromagnetic radiation of the first wavelength range into electromagnetic radiation of a second wavelength range which is at least partially different from the first wavelength range .

[0149] The conversion element 30 as shown in Figure 3 has the form of a layer . However, it could also be a casting that partially surrounds the semiconductor chip 20.

[0150] The structures 10 in the conversion element 30 have improved quantum dot stability even under operating conditions as explained above .

[0151] The features and exemplary embodiments described in connection with the figures can be combined with each other according to further exemplary embodiments, even if not all combinations are explicitly described. Furthermore, the 2024PF00852 October 28, 2025

[0152] P2024, 0745 WO N - 27 -

[0153] exemplary embodiments described in connection with the figures may have alternative or additional features as described in the general part .

[0154] The invention is not restricted to the exemplary embodiments by the description on the basis of said exemplary embodiments . Rather, the invention encompasses any new feature and also any combination of features, which in particular comprises any combination of features in the patent claims and any combination of features in the exemplary embodiments, even if this feature or this combination itself is not explicitly specified in the patent claims or exemplary embodiments .

[0155] This patent application claims the priority of US patent application 63 / 719, 684, the disclosure content of which is hereby incorporated by reference . 2024PF00852 October 28, 2025

[0156] P2024, 0745 WO N

[0157] - 28 -

[0158] References

[0159] 1 nanoparticle

[0160] 2 encapsulation

[0161] 3 surfactant

[0162] 10 structure

[0163] 20 semiconductor chip

[0164] 30 conversion element

[0165] 100 optoelectronic device

[0166] t time

[0167] PLQY photoluminescence quantum yield

Claims

2024PF00852 October 28 , 2025P2024 , 0745 WO N - 29 -Claims1 . A structure ( 10 ) , comprising :- a cluster of nanoparticles ( 1 ) , each nanoparticle ( 1 ) configured to convert electromagnetic radiation of a first wavelength range into electromagnetic radiation of a second wavelength range , and- an encapsulation ( 2 ) at least partially surrounding the cluster of nanoparticles ( 1 ) and comprising a metal oxide .2 . The structure ( 10 ) according to claim 1 , wherein the cluster of nanoparticles ( 1 ) comprises a si ze in the range of 10 nm to 10 pm inclusive .3 . The structure ( 10 ) according to any of the preceding claims , wherein the nanoparticles ( 1 ) comprise a Cd- free compound semiconductor material .4 . The structure ( 10 ) according to any of the preceding claims , wherein the encapsulation ( 2 ) comprises a thickness in the range of 1 nm to 500 nm inclusive .5 . The structure ( 10 ) according to any of the preceding claims , wherein the metal oxide of the encapsulation ( 2 ) is chosen from silica, alumino-silicate , zinc-silicate , alumina, titania, hafnia and combinations thereof .6 . The structure ( 10 ) according to any of the preceding claims , further comprising at least one additive within in the cluster .7 . The structure ( 10 ) according to the preceding claim, wherein the additive is chosen from pentaerythritol2024PF00852 October 28 , 2025P2024 , 0745 WO N 30tetrakis ( 3-mercaptopropionate ) , beta-mercaptoethanol , and combinations thereof .8 . The structure ( 10 ) according to any of claims 6 and 7 , wherein a ratio of an amount of additive to an amount of nanoparticles ( 1 ) in the cluster of nanoparticles ( 1 ) is in a range of 1 : 100 to 100 : 1 .9 . The structure ( 10 ) according to any of the preceding claims , wherein the nanoparticles ( 1 ) comprise ligands .10 . The structure ( 10 ) according to any of the preceding claims , further comprising a layer of surfactant ( 3 ) between the cluster of nanoparticles ( 1 ) and the encapsulation ( 2 ) .11 . A method for producing a structure ( 10 ) , the method comprising :- providing nanoparticles ( 1 ) , the nanoparticles ( 1 ) being configured to convert electromagnetic radiation of a first wavelength range into an electromagnetic radiation of a second wavelength range- forming a cluster of nanoparticles ( 1 ) , and- forming an encapsulation ( 2 ) at least partially encapsulating the cluster of nanoparticles ( 1 ) , the encapsulation ( 2 ) comprising a metal oxide .12 . The method according to the preceding claim, wherein forming the cluster of nanoparticles ( 1 ) includes the steps of- mixing the nanoparticles ( 1 ) with a first solvent , a surfactant ( 3 ) and a second solvent , wherein the first solvent and the second solvent are not miscible ,- forming an emulsion from the mixture , and2024PF00852 October 28, 2025P2024, 0745 WO N - 31 -- removing the first solvent .

13. The method according to any of claims 11 and 12, wherein forming an encapsulation (2 ) is performed by growing an encapsulation (2 ) comprising a metal oxide on the cluster of nanoparticles ( 1 ) .

14. The method according to the preceding claim, wherein the encapsulation (2 ) is grown by catalyst based method.

15. The method according to any of the claims 11 to 14, wherein at least one additive is added to the cluster of nanoparticles ( 1 ) before or after forming the cluster of nanoparticles ( 1 ) .

16. An optoelectronic device ( 100) , comprising:- a semiconductor chip (20) configured to emit electromagnetic radiation of a first wavelength range, and - a conversion element (30) comprising at least one structure ( 10) according to any of claims 1 to 10 and being configured to convert electromagnetic radiation of the first wavelength range into electromagnetic radiation of a second wavelength range .

17. The optoelectronic device ( 100) according to the preceding claim, wherein the semiconductor chip comprises a p-LED.

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