Structure, method for producing a structure, method for adjusting a water content of a structure, and optoelectronic device

Abstract

A structure is specified. According to one embodiment, the structure comprises a nanocrystal configured to convert a primary radiation into a secondary radiation and an encapsulation at least partially surrounding the nanocrystal, wherein the encapsulation comprises a humectant. Furthermore, a method for producing a structure, a method for adjusting a water content of a structure, and an optoelectronic device, in particular comprising a micro-LED, are specified.

Description

[0001] Description

[0002] STRUCTURE, METHOD FOR PRODUCING A STRUCTURE, METHOD FOR ADJUSTING A WATER CONTENT OF A STRUCTURE, AND OPTOELECTRONIC DEVICE

[0003] A structure, a method for producing a structure, a method for adjusting a water content of a structure, and an optoelectronic device are specified.

[0004] It is an object to provide a structure with improved efficiency. It is a further object to provide a simple method to produce such a structure. Additionally, it is an object to provide a simple method for adjusting the water content of such a structure. Furthermore, it is an object to provide an optoelectronic device with improved efficiency.

[0005] A structure is specified. The structure can comprise different elements, components, or parts with specific, in particular different, properties.

[0006] According to an embodiment, the structure comprises a nanocrystal configured to convert a primary radiation into a secondary radiation. In other words, the nanocrystal converts electromagnetic radiation of a first wavelength range, the primary radiation, into electromagnetic radiation of a second wavelength range, the secondary radiation. In particular, the nanocrystal absorbs the electromagnetic radiation of the first wavelength range, converts the electromagnetic radiation of the first wavelength range into the electromagnetic radiation of the second wavelength range, and emits the electromagnetic radiation of the second wavelength range. For example, the second wavelength range is in the visible or IR wavelength range. For instance, the second wavelength range is between 400 nm and 2000 nm, both inclusive. In particular, the second wavelength range is between 500 nm and 1000 nm, both inclusive.

[0007] In particular, the nanocrystal is a particle having a diameter of between and including 1 nm to 100 nm, for example between and including 2 nm and 20 nm. Due to their size, nanocrystals have different properties than a bulk material formed from the same material. For example, the nanocrystal is spherical, rod-shaped, or cuboid. A surface of the nanocrystal can be uniform or uneven.

[0008] For example, the nanocrystal comprises or consists of a semiconductor material. The semiconductor material is, for example, a III-V compound semiconductor material, a II-VI compound semiconductor material, or a II-III-V compound semiconductor material.

[0009] A III-V compound semiconductor material comprises at least one 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. A II-VI compound semiconductor material comprises at least one element of group 2 or 12 of the periodic table, for example Zn, Cd, Mg, and at least one element of group 16 of the periodic table, for example 0, S, Se, Te. A II-III-V compound semiconductor material comprises at least one element of group 2 or 12 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 nanocrystal comprises or consists of a sulfide, a selenide, a nitride or a phosphide. According to at least one embodiment , the structure comprises an encapsulation at least partially surrounding the nanocrystal . The encapsulation can comprise di f ferent layers and / or elements . The encapsulation can be configured or designed as a passivation layer for electronic passivation and / or as a protection layer for protecting components , for example , the nanocrystal , of the structure against degradation . In particular, the encapsulation completely surrounds the nanocrystal . The encapsulation can be in direct contact to the nanocrystal . Alternatively, further layers can be arranged between the nanocrystal and the encapsulation .

[0010] According to at least one embodiment , the encapsulation comprises a humectant . In particular, the humectant is a molecular motive that attracts , absorbs , retains , preserves , and releases moisture or water . In other words , the humectant is a moisture or water regulating species . For example , the humectant is configured to regulate a water content of the structure . In particular, the humectant is a hygroscopic or water-absorbing substance used to keep a speci fic water content within the structure . For example , the humectant balances or buf fers the water content within the structure by attracting, absorbing, retaining, preserving, and releasing moisture or water .

[0011] According to at least one embodiment , the structure comprises a nanocrystal configured to convert a primary radiation into a secondary radiation, and an encapsulation at least partially surrounding the nanocrystal , wherein the encapsulation comprises a humectant .

[0012] It is an idea of the present application to provide a structure having an ideal environment for a highly luminescent and stable nanocrystal due to the incorporation of a humectant within the encapsulation . The availability of water in the vicinity of the nanocrystal is useful in maintaining strong luminescence over time . However, excessive water content can lead to corrosion of the nanocrystal . Using humectants within the encapsulation allows to controllably tailor the content of trapped and absorbed water by controlling the transport and storage of water in the encapsulation and thus in the structure . This , in turn, will give more stable performance of the nanocrystal , for example , color as a function of temperature and li fetime , as well as longer-lasting nanocrystals in both operation and storage due to less corrosion .

[0013] According to at least one embodiment , the nanocrystal comprises a core and at least one shell . In particular, the nanocrystal is a quantum dot comprising a core and at least one shell . The core and / or the shell may comprise at least one semiconductor material . In particular, the core comprises a di f ferent semiconductor material than the shell . For instance , the at least one shell is epitaxially grown onto the core . The nanocrystal can comprise further shells and / or layers . For instance , the nanocrystal comprises a quantum well structure . For example , the nanoparticle is a core-shell quantum dot or a core-shell-shell quantum dot .

[0014] According to at least one embodiment , the humectant is configured for balancing the presence of water . In particular, the humectant balances the water content within the structure by attracting, absorbing, retaining, preserving, and releasing moisture or water . For example , the humectant acts as a buf fer to ensure that the structure will act to withstand changes in humidity by either releasing or absorbing humidity . A humectant configured for balancing the presence of water advantageously protects the nanocrystals against corrosion by limiting an excessive water content and, at the same time , maintains the luminescence of the nanocrystal over time by keeping water available within the structure .

[0015] According to at least one embodiment , the humectant is at least one of salts , small molecules , polymers , xerogels , and clay minerals . In particular, each type of humectant has a speci fic strength of water binding . For example , the structure comprises exactly one type of humectant .

[0016] Alternatively, the structure comprises more than one type of humectant .

[0017] Salts are chemical compounds composed of an ionic assembly of positively charged cations and negatively charged anions having no net electric charge . Salts can associate with water and thus retain water . Salts can include simple salts and complex salts .

[0018] In particular, simple salts comprise a cation selected from at least one of Li+, Na+, K+, NH4+, and Mg2+and an anion selected from at least one of Cl~, H3CCOCr, NO32~, and SG>42~ . For example , the simple salt is at least one of lithium chloride ( LiCl ) or lithium acetate (H3CCOOLi ) .

[0019] Complex salts are , in particular, polyatomic salts . For example , complex salts comprise a cation selected from at least one of Li+, and Na+and an anion selected from at least one of oleate , metaphosphate such as hexametaphosphate , and polyphosphate . Here and in the following, the term polyphosphate includes all polymeric ions formed from phosphate such as oligomers having a number of phosphate groups of ten or less and polymers having a number of phosphate groups of more than ten . For example , the complex salt is at least one of lithium oleate , lithium polyphosphate , or sodium hexametaphosphate .

[0020] Small molecules , in particular small molecules comprising at least one hydrophilic group such as a hydroxyl group, can retain water due to the formation of hydrogen bonds . For example , the small molecule is glycerol . Glycerol is also called glycerin or propane- 1 , 2 , 3-triol and comprises three hydroxyl groups .

[0021] Polymers are large molecules composed of a plurality of repeating subunits . Polymers can comprise several hydrophilic groups such as hydroxyl groups that can retain water due to the formation of hydrogen bonds . For example , the polymer is a polysaccharide or a polyalkylene glycol such as polyethylene glycol ( PEG) or polypropylene glycol ( PPG) .

[0022] Xerogels are solids formed from a gel by drying with unhindered shrinkage . In particular, xerogels have a porosity of 15% to 50% , both inclusive , a surface area of 150 to 900 m2 / g, both inclusive , and a pore si ze of 1 nm to 10 nm, both inclusive . Xerogels can retain water due to their high porosity and high surface area . For example , the xerogel is a silica gel .

[0023] Clay minerals are phyllosilicates such as hydrous aluminum phyllosilicates . In other words , clay minerals are sheet silicates such as hydrous aluminum sheet silicates . Clay minerals can retain water between the individual sheets due to their sheet-like structure . For example , the clay mineral is kaolinite or smectite . Kaolinite has the chemical composition A12Si20s ( OH) 4 . In ceramic applications , the formula for kaolinite is written in terms of oxides and thus the formula is AI2O3 • 2S1O2 • 2H2O . Kaolinite is a layered silicate material , with one sheet of silica tetrahedra linked through oxygen atoms to one sheet of alumina octahedra . Smectite is a mineral mixture of various phyllosilicates having a three-layered structure of two layers of silica tetrahedra which are cross-linked via one layer of AI2O3 or Fe2O3octahedra .

[0024] According to at least one embodiment , the encapsulation comprises a passivating layer at least partially, in particular completely, surrounding the nanocrystal . A diameter of a nanocrystal surrounded by a passivating layer can be less than 1 pm, in particular between and including 1 nm and 500 nm or between and including 1 nm and 100 nm . In particular, the passivating layer comprises or consists of a metal oxide such as silica, alumina, zirconia, hafnium oxide , strontium oxide , or tin oxide . For example , the passivating layer comprises or consists of silica . Metal oxides , in particular silica, can advantageously be homogeneously deposited around the nanocrystal , for example , with wet or dry chemical deposition methods . A passivating layer surrounding the nanocrystal advantageously increases the robustness of the nanocrystal .

[0025] According to at least one embodiment , the passivating layer comprises the humectant . In particular, the humectant is arranged within the passivating layer . In other words , the passivating layer at least partially, in particular completely, surrounds the humectant . In particular, the humectant is present in the passivating layer in the form of humectant molecules or humectant particles . The humectant particles can have a diameter of less than 1 pm, for example , between and including 1 nm and 500 nm or between and including 1 nm and 100 nm . The humectant can have a gradient within the passivating layer . For example , a concentration of the humectant decreases with increasing distance from the nanocrystal or a concentration of the humectant increases with increasing distance from the nanocrystal . The passivating layer comprising the humectant advantageously allows a close contact and an improved interaction between the nanocrystal and the humectant .

[0026] According to at least one embodiment , the humectant is embedded in the passivating layer . In particular, every type of humectant described herein can be embedded in the passivating layer . For example , the humectant is a simple salt , a complex salt , a small molecule , a polymer, a xerogel , a clay mineral , or combinations thereof . Embedding a humectant in the passivating layer allows a close contact and an improved interaction between the nanocrystal and the humectant .

[0027] According to at least one embodiment , a simple salt is embedded in the passivating layer and a concentration of the simple salt in the passivating layer is 1 wt . -% (weight-% ) to 30 wt . -% , both inclusive , in particular 3 wt . -% to 10 wt . -% , both inclusive .

[0028] According to at least one embodiment , lithium chloride is embedded in the passivating layer . Embedding lithium chloride in a passivating layer of a metal oxide results in lithium chloride inside the oxide network of the passivating layer and lithium-metal oxide complexes , both of which act as humectants .

[0029] According to at least one embodiment , the humectant is covalently bonded to a material of the passivating layer . In other words , the humectant comprises a covalent bond with a material of the passivating layer . In particular, the humectant is polyethylene glycol ( PEG) or polypropylene glycol ( PPG) . Both polyethylene glycol and polypropylene glycol can be covalently incorporated into the oxide network of a passivating layer of a metal oxide during the formation of the passivating layer . A humectant covalently bonded to the passivating layer is advantageously incorporated into the passivating layer by a strong chemical interaction .

[0030] According to at least one embodiment , a material of the passivating layer is the humectant . In particular, the passivating layer is formed of the humectant . For example , the passivating layer consists of the humectant . Alternatively, the passivating layer can comprise further materials such as metal oxides that are not humectants . In particular, the passivating layer comprises 1 % of humectant to 100 % of humectant , both inclusive . For example , the humectant is an ammonium silicate or an alkali silicate such as sodium silicate or lithium silicate . With a humectant as a material of the passivating layer, the nanocrystal is protected by a dual-purpose passivating and humectant layer . The dual-purpose layer advantageously facilitates the use of high loading of humectants .

[0031] According to at least one embodiment , a further humectant is embedded in the passivating layer having the humectant as a material of the passivating layer . In other words , the passivating layer comprises two different humectants, wherein one humectant is embedded in the passivating layer and one humectant is a material of which the passivating layer is formed. The further humectant is, for example, a complex salt or a clay mineral. In a structure with two different humectants, the strength of water binding can advantageously be tailored to specific applications.

[0032] According to at least one embodiment, two materials of the passivating layer are humectants. In particular, the passivating layer is formed of two humectants. The concentration of the two humectants in the resulting passivating layer can be the same or different. In other words, a concentration of the two humectants can be varied in the passivating layer. For example, the humectants are sodium silicate and lithium silicate. Since two materials of the passivation layer are humectants, a passivation layer with a finely tuned composition that can be tailored to specific conditions can advantageously be obtained.

[0033] According to at least one embodiment, the encapsulation comprises a humectant layer abutting the passivating layer, wherein the humectant layer comprises or consists of the humectant. In other words, the humectant layer is arranged directly adjacent to the passivating layer. In particular, the humectant layer comprises the humectant and a matrix material such as silica, silicone, or an organic polymer. The humectant can be embedded in the matrix material. For example, the humectant is a complex salt such as a polyphosphate, a polymer, or a clay mineral such as smectite or kaolinite. For instance, small clay mineral particles can be embedded in the silica. Alternatively, complex salt grains can be incorporated in silica or silicone or an organic polymer . Alternatively, the humectant layer can consist of the humectant . In particular, the humectant layer is formed by the humectant . A humectant layer abutting the passivating layer advantageously places small demands on the compatibility of the respective components while placing them in intimate contact .

[0034] According to at least one embodiment , the humectant layer is arranged at least partially, in particular completely, between the nanocrystal and the passivating layer . In particular, the humectant layer is in direct contact with the nanocrystal and the passivating layer . For example , the humectant layer comprises or consists of polyphosphate salts that are arranged on a surface of the nanocrystal prior to adding the passivating layer . A humectant layer between the nanocrystal and the passivating layer allows a close contact and an improved interaction between the nanocrystal and the humectant in the humectant layer .

[0035] According to at least one embodiment , the humectant layer at least partially, in particular completely, surrounds the passivating layer . In particular, the humectant layer is in direct contact with the passivating layer on a side of the passivating layer facing away from the nanocrystal . For example , the humectant layer comprises or consists of simple salts or polyphosphate salts that are arranged on a surface of the passivating layer facing away from the nanocrystal after the nanocrystal is surrounded by the passivating layer . Advantageously, a humectant layer surrounding the passivating layer can be added independently of the formation of the passivating layer after the passivating layer is arranged on the nanocrystal . According to at least one embodiment , the encapsulation comprises a plurality of passivating layers and humectant layers arranged in an alternating manner . In other words , the encapsulation comprises a sequential structure of a plurality of passivating layers and a plurality of humectant layers . In particular, the encapsulation comprises at least two , in particular at most ten, passivating layers and at least two , in particular at most ten, humectant layers arranged in an alternating manner . The material of the plurality of passivating layers can be the same for all passivating layers , whereas the humectant layers can comprise the same humectant or di f ferent humectants . For example , the passivating layers are silica layers and the humectant layers comprise a clay mineral such as smectite or kaolinite . Alternatively, the passivating layers can be silica layers and one or more humectant layers comprise one humectant such as a clay mineral and one or more humectant layers comprise a di f ferent humectant such as a di f ferent clay mineral or a salt . Passivating layers and humectant layers arranged in an alternating manner can increase the advantageous ef fects of the incorporation of a humectant in the structure . By having di f ferent humectants in the di f ferent humectant layers , the strength of water binding can advantageously be tailored to speci fic applications .

[0036] According to at least one embodiment , the structure further comprises a barrier layer at least partially, in particular completely, surrounding the encapsulation . In particular, the barrier layer is configured for slowing or preventing the di f fusion of water in and out of the encapsulation . For example , the barrier layer is the outermost layer of the structure . A barrier layer can be advantageous for applications having an elevated operating temperature in which a structure without a barrier layer becomes dehydrated due to water evaporation .

[0037] According to at least one embodiment , the barrier layer hermetically seals the encapsulation . In other words , the barrier layer is an impermeable barrier layer . In particular, the barrier layer is watertight such that no or nearly no water can enter or leave the structure . For example , a water vapor transmission rate of the barrier layer ranges from 10~2g / m2 / day to 10~6g / m2 / day, both inclusive . A thickness of the barrier layer can be between 10 nm and 100 nm, both inclusive . For example , the barrier layer is ethylene cellulose (EC ) or an atomic layer deposition (ALD) layer such as an ALD layer of alumina . A barrier layer hermetically sealing the encapsulation advantageously prevents any water from leaving the structure and at the same time shields the nanocrystals from water entering the structure from the outside .

[0038] According to at least one embodiment , the barrier layer is a semipermeable layer . A semipermeable layer has the property of being partially permeable . In other words , a semipermeable layer allows only speci fic compounds or molecules to pass through and retains other compounds or molecules . In particular, the semipermeable layer is partially permeable for water molecules . In other words , the semipermeable layer only allows a portion of the water located within the structure to leave the structure . Further, the semipermeable layer allows only a portion of water present outside of the structure to pass through the semipermeable layer into the structure . For example , a water vapor transmission rate of the barrier layer ranges from 10~2g / m2 / day to 10~6g / m2 / day, both inclusive . A thickness of the barrier layer can be between 10 nm and 100 nm, both inclusive . For example , the barrier layer is an organic polymer . A semipermeable layer advantageously slows the di f fusion of water in and out of the structure .

[0039] According to at least one embodiment , the barrier layer comprises a semipermeable layer and a water sealant layer . In particular, the semipermeable barrier layer is arranged on the encapsulation and the water sealant layer is arranged on the semipermeable barrier layer . For example , the water sealant layer is an ALD layer . In this instance , water can di f fuse through the semipermeable barrier layer to the humectant and can advantageously allow a small amount of water to be entrapped in the passivating layer by the humectant , while the water sealant layer prevents a dehydration of the structure .

[0040] According to at least one embodiment , the encapsulation comprises a first matrix material , wherein the humectant and the nanocrystal are embedded in the first matrix material . In this embodiment , a passivating layer at least partially, in particular completely, surrounds the nanocrystal . The nanocrystal and the humectant are arranged in the same matrix material , but physically separated from each other . In particular, the humectant is present in the form of humectant particles . For example , a diameter the humectant particles is less than 1 pm, in particular between and including 1 nm and 500 nm or between and including 1 nm and 100 nm . For example , the humectant particles are xerogel particles such as silica gel particles , complex salts such as polyphosphates , or clay minerals such as smectite or kaolinite . In particular, a plurality of nanocrystals and a plurality of humectant particles is embedded in the first matrix material . The first matrix material can be arranged in the form of a layer or a casting . For example , the first matrix material is silicone . Embedding the nanocrystal and the humectant in a first matrix material advantageously allows complete freedom in the nature of the humectant .

[0041] Furthermore , a method for producing a structure is speci fied . In particular, the structure described herein is produced by the method for producing a structure . Thus , embodiments , features , and advantages described in combination with the structure also apply to the method for producing a structure and vice versa .

[0042] According to at least one embodiment , the method comprises providing a nanocrystal configured to convert a primary radiation into a secondary radiation, and providing an encapsulation at least partially surrounding the nanocrystal , wherein the encapsulation comprises a humectant .

[0043] In particular, the method for producing a structure is a method for producing a plurality of structures . In this instance , a plurality of nanocrystals are provided and each nanocrystal is at least partially surrounded by the encapsulation comprising a humectant .

[0044] Advantageously, the method is a simple and ef ficient method for producing a structure having an ideal environment for highly luminescent and stable nanocrystal by incorporating a humectant within an encapsulation of the structure .

[0045] According to at least one embodiment , providing the encapsulation includes forming a passivating layer at least partially, in particular completely, surrounding the nanocrystal . In particular, the passivating layer is synthesi zed using a reverse micelle procedure . For example , the passivating layer is produced as follows : The nanocrystal or the plurality of nanocrystals is suspended in a non-polar hydrophobic solvent , forming a first solution . To the first solution, a surfactant and subsequently, a metal oxide precursors , other reagents and catalysts are added to initiate the metal oxide growth on a surface of the nanocrystal .

[0046] According to at least one embodiment , a material of the passivating layer is the humectant . In particular, the passivating layer is produced as described above and a humectant precursor is added as a reagent instead of or in addition to the metal oxide precursor . For example , the humectant precursor is a precursor for a silica-based humectant such as alkali silicates or ammonium silicates . By using a humectant as a material of the passivating layer, a dual-purpose passivating and humectant layer with a high loading of humectant can be produced simply and ef ficiently with very few steps .

[0047] According to at least one embodiment , two materials of the passivating layer are humectants . In particular, the passivating layer is produced as described above and two humectant precursors are added as reagents instead of or in addition to the metal oxide precursor . For instance , the two humectant precursors are added in di f ferent amounts . For example , the humectant precursors are sodium silicate and lithium silicate . Using two di f ferent humectant precursors as materials of the passivating layer advantageously allows to simply produce a passivating layer with a fine-tuned composition . According to at least one embodiment , the humectant is provided on a surface of the nanocrystal before forming the passivating layer . In particular, a humectant layer comprising the humectant is provided on a surface of the nanocrystal . For example , a surface of the nanocrystal is treated with a polyphosphate salt to create a charged nanocrystal surface and subsequently, the passivation layer is produced on to the charged nanocrystal surface . Providing the humectant on the surface of the nanocrystal before forming the passivating layer allows a close contact and an improved interaction between the nanocrystal and the humectant , while , at the same time , places small demands on the compatibility of the respective components .

[0048] According to at least one embodiment , the humectant is embedded in the passivating layer during forming the passivating layer . In particular, the humectant is added to the first solution at the same time as the metal oxide precursor is added . The humectant can be preformed and added to the first solution . This may improve the accuracy and yield with which a targeted humectant is formed and a final chemical composition is achieved . Alternatively or additionally, humectant precursors can be added to the first solution and the humectant is formed in situ . The in situ formation may allow a closed contact and a greater interaction between nanocrystal and humectant . In particular, each of the types of humectants described above can be used in this method . For example , the humectant is a simple salt such as lithium chloride . The addition of lithium chloride will result in lithium chloride inside the oxide network of the passivating layer and lithium-metal oxide complexes in the passivating layer, both of which act as humectants . For instance , the humectant is polyethylene glycol or polypropylene glycol . Polyethylene glycol or polypropylene glycol can be covalently incorporated into the metal oxide network of the passivating layer during forming the passivating layer . Embedding the humectant in the passivating layer during forming the passivating layer advantageously combines the process of forming the passivating layer with minor variations to create structures comprising a humectant in the passivating layer .

[0049] According to at least one embodiment , the humectant is added after forming the passivating layer . Advantageously, adding the humectant after forming the passivating layer allows the incorporation of the humectant in the structure that is independent of the formation of the passivating layer .

[0050] According to at least one embodiment , a humectant layer comprising the humectant is provided on a surface of the passivating layer . In particular, the nanocrystal is surrounded by the passivating layer as described above and subsequently, a humectant layer is deposited on the surface of the passivating layer . For example , simple salts or complex salts such as polyphosphates are deposited from polar solutions . Advantageously, a humectant layer surrounding the passivating layer can be added independently of the formation of the passivating layer after the passivating layer is arranged on the nanocrystal .

[0051] According to at least one embodiment , the humectant is provided on a surface of the passivating layer and di f fuses into the passivating layer . In particular, the nanocrystal is surrounded by the passivating layer as described above and subsequently, the humectant is driven into the preformed oxide of the passivating layer . For example , simple salts may be precipitated onto and into the passivating layer after forming the passivating layer . For example , lithium chloride powder can be added after forming the passivating layer to yield physically adsorbed, but not absorbed humectant species . In particular, the humectant such as simple salts equilibrates throughout the passivating layer . Alternatively, the humectant such as clay minerals or molecules that bind tightly to the metal oxide of the passivating layer forms a gradient in the passivating layer such that a concentration of the humectant increases with increasing distance from the nanocrystal . Such a post-synthetic addition of the humectant can advantageously yield greater control over properties such as grain si ze which may af fect the kinetics of water absorption and desorption .

[0052] According to at least one embodiment , the amount of humectant in the passivating layer is controlled . In particular, an amount of humectant or humectant precursor is added at the beginning of the reaction that forms the passivating layer and an additional amount of humectant or humectant precursor is added one or more additional times throughout the reaction that forms the passivating layer . For example , a syringe pump is used to increase the overall amount of humectant or humectant precursor and dispensing is performed slowly during the reaction time . By controlling the amount of humectant in the passivating layer, the humectant can comprise a gradient in the passivating layer . Controlling the amount and rate of reagents entering the reaction mixture in the first solution can be advantageous to avoid disrupting the reaction that forms the passivating layer . According to at least one embodiment , the passivating layer at least partially surrounds the nanocrystal , and the humectant and the nanocrystal are embedded in a first matrix material . In particular, a plurality of nanocrystals and a plurality of humectant particles are embedded in the first matrix material . Embedding the humectant and the nanocrystal in the same matrix material advantageously allows complete freedom in the nature of the humectant .

[0053] According to at least one embodiment , the method further comprises adj usting the water content of the humectant . The water content of the humectant can be adj usted by exposing the structure to an environment of a speci fic humidity . In particular, the structure is exposed to an environment of a speci fic humidity for a speci fic amount of time and at a speci fic temperature . For example , the temperature is selected between 0 ° C and 100 ° C . The water content can be adj usted in a humidity chamber . For example , the water content of the humectant can be decreased . Alternatively, the water content of the humectant can be increased . Adj usting the water content of the humectant advantageously permits to achieve a desired water content in the structure .

[0054] According to at least one embodiment , the method further comprises providing a barrier layer at least partially, in particular completely, surrounding the encapsulation . In particular, providing the barrier layer includes hermetically sealing the encapsulation by forming an impermeable barrier layer . Alternatively, providing the barrier layer includes forming a semipermeable barrier layer on the encapsulation . For instance , a semipermeable barrier layer is provided on the encapsulation, subsequently, water is added, and subsequently a water sealant layer such as an ALD layer is provided on the semipermeable barrier layer. In this instance, water can diffuse through the semipermeable barrier layer to the humectant and can advantageously allow a small amount of water to be entrapped in the passivating layer by the humectant, while the water sealant layer prevents a dehydration of the structure.

[0055] Furthermore, a method for adjusting a water content of a structure is specified. In particular, a water content of the structure described herein is adjusted by the method for adjusting a water content of a structure. Thus, embodiments, features, and advantages described in combination with the structure and the method for producing a structure also apply to the method for adjusting a water content of the structure and vice versa.

[0056] According to at least one embodiment, the method comprises exposing the structure to an environment of a specific humidity, wherein the humectant releases or absorbs water. In particular, the structure is exposed to an environment of a specific humidity for a specific amount of time and at a specific temperature. For example, the temperature is selected between 0 °C and 100 °C. The water content can be adjusted in a humidity chamber. For example, the water content of the humectant can be decreased by exposing the structure to a dry environment having a lower humidity than the structure and / or a high temperature. In this instance, the humectant releases water. Alternatively, the water content of the humectant can be increased by exposing the structure to a humid environment having a higher humidity than the structure. In this instance, the humectant absorbs water . In particular, the method for adj usting a water content of a structure is a method for adj usting a water content of the plurality of structures . In this instance , a plurality of structures is exposed to an environment of a speci fic humidity and each humectant reduces or absorbs water .

[0057] Advantageously, the method for adj usting the water content of the humectant advantageously permits to achieve a desired water content in the structure , where the humectant in the structure acts as a buf fer to ensure that the structure will act to withstand further changes in humidity once removed from the humidity chamber . The method of adj usting the water content of the humectant can be advantageously employed after the structure has been exposed to dry conditions and / or high temperature conditions such as assembly processes performed at high temperatures .

[0058] Furthermore , an optoelectronic device is speci fied . In particular, the optoelectronic device comprises at least one structure described herein . Thus , embodiments , features , and advantages described in combination with the structure , the method for producing a structure , and the method for adj usting a water content of a structure also apply to the optoelectronic device and vice versa .

[0059] According to an embodiment , the optoelectronic device comprises a semiconductor chip configured to emit a primary radiation . In other words , the semiconductor chip is configured to emit electromagnetic radiation of a first wavelength range . In particular, the primary radiation comprises wavelengths in the ultraviolet to blue spectral region . According to at least one embodiment , the optoelectronic device comprises a conversion element comprising at least one structure , in particular a plurality of structures , described herein . In particular, the conversion element is configured to convert at least a portion of the primary radiation into a secondary radiation . In other words , the conversion element converts the electromagnetic radiation of the first wavelength range into electromagnetic radiation of a second wavelength range . For example , the first wavelength range is at least partially di f ferent from the second wavelength range . For instance , the second wavelength range comprises wavelengths having a lower energy compared to the wavelengths in the first wavelength range . In particular, an ability of the conversion element to convert electromagnetic radiation is attributed to the structure which comprises the nanocrystal converting primary radiation into secondary radiation .

[0060] According to at least one embodiment , the optoelectronic device comprises a semiconductor chip configured to emit a primary radiation, and a conversion element comprising at least one structure disclosed herein .

[0061] Advantageously, the optoelectronic device described herein has an improved ef ficiency, in particular, an increased operating li fetime in corrosive conditions due to the incorporation of a humectant in the structure . In this way, the conversion element can maintain its conversion ef ficiency over a longer time compared to conversion elements comprising structures without humectants .

[0062] According to at least one embodiment , the semiconductor chip is a micro-LED . Here and in the following, LED is an abbreviation for the term " light-emitting diode" . Micro-LEDs may have 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, for instance in plan view of layers of a layer stack, of a luminous surface smaller than or equal to 70 micrometers , for example smaller than or equal to 50 micrometers . For example , the micro-LED is a light-emitting diode wherein a growth substrate is removed, such that a thickness of the micro-LED is , for instance , between and including 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 .

[0063] According to at least one embodiment , the conversion element comprises a second matrix material and the at least one structure , in particular the plurality of structures , is embedded in the second matrix material . In particular, the structure comprises a nanocrystal at least partially surrounded by a passivating layer, wherein a humectant is embedded in the passivating layer . Alternatively, the structure can comprise a nanocrystal at least partially surrounded by a passivating layer, wherein a material of the passivating layer is the humectant . Alternatively, the structure can comprise a nanocrystal at least partially surrounded by a passivating layer, wherein a humectant layer comprising a humectant abuts the passivating layer . For example , the second matrix material is silicone , polysiloxane , or epoxy . In this instance , the conversion element is formed as a layer or a casting . According to at least one embodiment , the conversion element consists of the structure comprising a nanocrystal at least partially surrounded by a passivating layer, wherein a humectant and the nanocrystal are embedded in a first matrix material . In this instance , the conversion element is formed as a layer or a casting .

[0064] According to at least one embodiment , the optoelectronic device is used in augmented reality and / or virtual reality applications , in automotive applications , and / or for illumination .

[0065] Advantageous embodiments and developments of the structure , the method for producing a structure , the method for adj usting a water content of the structure , and the optoelectronic device will become apparent from the exemplary embodiments described below in conj unction with the figures .

[0066] In the figures :

[0067] Figure 1 shows a schematic illustration of a nanocrystal according to an exemplary embodiment .

[0068] Figures 2 , 3 , and figures 5 to 9 each show a schematic illustration of a structure according to di f ferent exemplary embodiments .

[0069] Figure 4 shows the photoluminescence quantum yield of a structure according to an exemplary embodiment and a comparative example . Figures 11 and 12 each show a schematic illustration of an optoelectronic device according to different exemplary embodiments .

[0070] 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.

[0071] Figure 1 shows a schematic illustration of a nanocrystal 2. The nanocrystal 2 comprises a core 21 and a shell 22. The core 21 and / or the shell 22 comprise at least one semiconductor material. The semiconductor material is, for example, a III-V compound semiconductor material, a II-VI compound semiconductor material, or a II-III-V compound semiconductor material. In particular, the core 21 comprises a different semiconductor material than the shell 22. The nanocrystal 2 can comprise further shells and / or layers.

[0072] Figure 2 shows a schematic illustration of a structure 1 described herein according to a first exemplary embodiment. The structure 1 comprises a nanocrystal 2 and an encapsulation 3. The encapsulation 3 is a passivating layer 31 surrounding the nanocrystal 2. For example, the passivating layer 31 is a silica layer. A humectant 4 is embedded in the passivating layer 31. The humectant 4 can be at least one of a simple salt such as lithium chloride, a complex salt such as sodium hexametaphosphate, a small molecule such as glycerol, a polymer such as polyethylene glycol, polypropylene glycol, or a polysaccharide, a xerogel such as a silica gel , and a clay mineral such as smectite or kaolinite . The structure 1 further comprises a barrier layer 5 surrounding the encapsulation 3 . For example , the barrier layer 5 is an ethylene cellulose layer, an ALD layer made of alumina, or a semipermeable barrier layer made of an organic polymer .

[0073] The structure 1 of the first exemplary embodiment can be produced as follows :

[0074] A nanocrystal 2 , in particular a plurality of nanocrystals 2 , is provided by suspending the nanocrystal 2 or the plurality of nanocrystals 2 in a nonpolar hydrophobic solvent , thus forming a first solution . The passivating layer 31 is synthesi zed by using a reverse micelle procedure . Therefore , a surfactant and subsequently, metal oxide precursors such as silica precursors , other reagents and catalysts are added to the first solution to initiate the metal oxide growth on a surface of the nanocrystal 2 .

[0075] The humectant 4 can be added during the metal oxide synthesis before puri fication . The humectant 4 can be preformed and subsequently added . Alternatively or additionally, a humectant precursor can be added and the humectant 4 is formed in situ . For example , the humectant 4 is added in form of a simple salt such as lithium chloride . The addition of simple salt such as lithium chloride results in lithium chloride inside the oxide network and lithium-metal oxide complexes such as lithium-silicate complexes , both of which act as humectants 4 . Thus , lithium chloride acts both as a preformed humectant 4 in the form of lithium chloride inside the oxide network and as a humectant precursor that forms a humectant 4 in the form of the lithium-metal oxide complex in situ . The amount of humectant 4 in the passivating layer 31 can be controlled by adding an amount of humectant 4 or humectant precursor at the beginning of the reaction that forms the passivating layer 31 and additional amounts of humectant 4 or humectant precursor are inj ected one or more additional times throughout the reaction that forms the passivating layer 31 . For example , a syringe pump is used to increase the overall amount of humectant 4 or humectant precursor . With a syringe pump, dispensing can be performed slowly during the reaction time .

[0076] Alternatively to the addition of the humectant 4 during the metal oxide synthesis , the humectant 4 can be added onto the metal oxide passivating layer 31 after the metal-oxide growth and di f fuses into the passivating layer 31 . For example , the humectant 4 is driven into the preformed metal oxide of the passivating layer 31 in the form of a simple salt such as lithium chloride . The addition of lithium chloride powder on the preformed metal oxide of the passivating layer 31 yields physically adsorbed, but not absorbed humectant species .

[0077] Figure 3 shows a schematic illustration of a structure 1 described herein according to a second exemplary embodiment . The second exemplary embodiment corresponds substantially to the first exemplary embodiment shown in figure 2 . In contrast to the first exemplary embodiment , the passivating layer 31 comprises an increased amount of humectant 4 . The structure 1 according to the second embodiment can be produced like the structure 1 according to the first embodiment .

[0078] Figure 4 shows the photoluminescence quantum yield of a structure 1 according to the first embodiment as shown in figure 2 and a comparative example . In the diagram in figure 4 , the photoluminescence quantum yield is plotted against the operating time t in hours . Curve 4- 1 shows the photoluminescence quantum yield as a function of time of a structure 1 comprising lithium acetate and potassium acetate as a humectant . Curve 4-2 shows the photoluminescence quantum yield as a function of time of a comparative example of a structure without a humectant . As can be seen in figure 4 , the luminescence of the structure 1 comprising a humectant 4 can be maintained longer ( curve 4- 1 ) than the luminescence of a structure without a humectant ( curve 4-2 ) . Without a humectant , the photoluminescence quantum yield decreases rapidly after a short amount of time ( curve 4-2 ) , whereas the photoluminescence quantum yield of the structure 1 with a humectant 4 only slightly decreases over a signi ficantly longer period of time ( curve 4- 1 ) .

[0079] Figure 5 shows a schematic illustration of a structure 1 described herein according to a third exemplary embodiment . The third exemplary embodiment corresponds substantially to the first exemplary embodiment shown in figure 2 . In contrast to the first exemplary embodiment , a material of the passivating layer 31 is the humectant 4 . The passivating layer 31 is formed of the humectant 4 either partially or completely . In particular, the passivating layer 31 comprises 1 % of humectant to 100 % of humectant 4 , both inclusive . For example , the humectant 4 is an ammonium silicate or an alkali silicate such as sodium silicate or lithium silicate .

[0080] The structure 1 according to the third embodiment can substantially be produced like the structure 1 according to the first embodiment . The method for producing the structure 1 according to the third embodiment di f fers in that the passivating layer 31 is produced as described above and a humectant precursor is added as a reagent instead of or in addition to the metal oxide precursor . For example , the humectant precursor is a precursor for a silica-based humectant such as alkali silicates or ammonium silicates .

[0081] Instead of adding one humectant precursor, two humectant precursors can be added as reagents instead of or in addition to the metal oxide precursor . For instance , the two humectant precursors are added in di f ferent amounts . For example , the humectant precursors are sodium silicate and lithium silicate .

[0082] Figure 6 shows a schematic illustration of a structure 1 described herein according to a fourth exemplary embodiment . The fourth exemplary embodiment corresponds substantially to the third exemplary embodiment shown in figure 5 . In contrast to the third exemplary embodiment , the passivating layer 31 comprises an increased amount of humectant 4 . In particular, the passivating layer 31 consists of the humectant 4 . The structure 1 according to the fourth embodiment can be produced like the structure 1 according to the third exemplary embodiment .

[0083] Figure 7 shows a schematic illustration of a structure 1 described herein according to a fi fth exemplary embodiment . The fi fth exemplary embodiment corresponds substantially to the first exemplary embodiment shown in figure 2 . In contrast to the first exemplary embodiment , the encapsulation 3 comprises the passivating layer 31 and a humectant layer 32 . In particular, the passivating layer 31 can be free of humectant . The humectant layer 32 comprises or consists of the humectant 4 . In particular, the humectant layer 32 comprises the humectant 4 and a matrix material . The humectant layer 32 is arranged in-between the nanocrystal 2 and the passivating layer 31 such that it abuts both of them .

[0084] The structure 1 according to the fi fth exemplary embodiment is produced as follows :

[0085] A surface of the nanocrystal 2 is treated with the humectant 4 , for example a complex salt or a clay mineral , to create a charged nanocrystal surface with the humectant layer 32 . Subsequently, the passivating layer 31 is grown onto the humectant layer 32 as described above in conj unction with the first embodiment of figure 2 .

[0086] Figure 8 shows a schematic illustration of a structure 1 described herein according to a sixth exemplary embodiment . The sixth exemplary embodiment corresponds substantially to the fi fth exemplary embodiment shown in figure 7 . In contrast to the fi fth exemplary embodiment , the humectant layer 32 is arranged on a surface of the passivating layer 32 facing away from the nanocrystal 2 .

[0087] The structure 1 according to the sixth exemplary embodiment is produced as follows :

[0088] The passivating layer 31 is grown onto a surface of the nanocrystal 2 as described above in conj unction with the first embodiment of figure 2 . Subsequently, the humectant layer 32 comprising the humectant 4 such as a simple salt or a complex salt is deposited onto a surface of the passivating layer 31 facing away from the nanocrystal 2 from polar solutions .

[0089] The structures 1 according to the fi fth and sixth exemplary embodiment described in conj unction with figure 7 and 8 can comprise a plurality of passivating layer 31 and humectant layers 32 arranged in an alternating manner . Such a structure 1 thus comprises a sequential structure . Such a structure 1 can be produced by repeating the method steps of providing a humectant layer 32 and providing a passivating layer 31 .

[0090] Figure 9 shows a schematic illustration of a structure 1 described herein according to a seventh exemplary embodiment . The structure 1 comprises a nanocrystal 2 and an encapsulation 3 . The encapsulation 3 comprises a passivating layer 31 surrounding the nanocrystal 2 . For example , the passivating layer 31 is a silica layer . The encapsulation 3 further comprises a first matrix material 33 , for example , silicone . The nanocrystal 2 and a humectant 4 are embedded in the first matrix material 33 . The humectant 4 is in particular embedded in the first matrix material 33 in the form of humectant particles . The humectant particles can have a diameter of less than 1 pm, for example , between and including 1 nm and 500 nm or between and including 1 nm and 100 nm . The humectant 4 can be at least one of a simple salt such as lithium chloride , a complex salt such as sodium hexametaphosphate , a small molecule such as glycerol , a polymer such as polyethylene glycol , polypropylene glycol , or a polysaccharide , a xerogel such as a silica gel , and a clay mineral such as smectite or kaolinite .

[0091] Figure 10 shows a schematic illustration of a structure 1 described herein according to an eighth exemplary embodiment . The eighth exemplary embodiment corresponds substantially to the seventh exemplary embodiment shown in figure 9 . In contrast to the seventh exemplary embodiment , the structure 1 comprises a plurality of nanocrystals 2 and a plurality of humectant particles . The water content of any of the structures 1 as shown in conj unction with figures 2 , 3 , and 5 to 10 can be adj usted by exposing the structure 1 to an environment of a speci fic humidity . In particular, the structure 1 is exposed to an environment of a speci fic humidity for a speci fic amount of time and at a speci fic temperature . For example , the temperature is selected between 0 ° C and 100 ° C . For instance , the humectant 4 can release water and thus the water content of the structure 1 can be decreased .

[0092] Alternatively, the humectant 4 can absorb water and thus the water content of the structure 1 can be increased .

[0093] Figure 11 shows a schematic illustration of an optoelectronic device 10 described herein according to a first exemplary embodiment . The optoelectronic device comprises a semiconductor chip 11 configured to emit a primary radiation of a first wavelength range . The semiconductor chip can be a micro-LED . For example , the first wavelength range is in the blue spectral region .

[0094] A conversion element 12 is arranged on a radiation exit surface of the semiconductor chip 11 . The conversion element 12 can be arranged directly on the radiation exit surface or in the distance to the radiation exit surface . The conversion element 12 can be in the form of a layer or a casting . The conversion element 12 converts the primary radiation into secondary radiation of a second wavelength range . The conversion element comprises or consists of at least one structure 1 described herein .

[0095] For example , the conversion element 12 comprises at least one structure 1 , in particular a plurality of structures 1 , as shown in conj unction with figures 2 , 3 , and 5 to 9 . In particular, the at least one structure 1 may be embedded in a second matrix material such as silicone , polysiloxane , or epoxy .

[0096] Figure 12 shows a schematic illustration of an optoelectronic device 10 described herein according to a second exemplary embodiment . The second exemplary embodiment corresponds substantially to the first exemplary embodiment shown in figure 11 . In contrast to the first exemplary embodiment , the semiconductor chip 11 and the conversion element 12 are arranged in the recess of the housing . The conversion element 12 comprises the structure 1 as shown in conj unction with figure 10 in the form of a casting around the semiconductor chip 11 .

[0097] The features and exemplary embodiments described in connection with the figures can be combined with each other according to further exemplary embodiments , even i f not all combinations are explicitly described . Furthermore , the exemplary embodiments described in connection with the figures may have alternative or additional features as described in the general part .

[0098] 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 i f this feature or this combination itsel f is not explicitly speci fied in the patent claims or exemplary embodiments . This patent application claims the priority of US patent application 63 / 508,912, the disclosure content of which is hereby incorporated by reference.

[0099] References

[0100] 1 structure

[0101] 2 nanocrystal

[0102] 21 core

[0103] 22 shell

[0104] 3 encapsulation

[0105] 31 passivating layer

[0106] 32 humectant layer

[0107] 33 first matrix material

[0108] 4 humectant

[0109] 5 barrier layer

[0110] 10 optoelectronic device

[0111] 11 semiconductor chip

[0112] 12 conversion element

[0113] 4- 1 curve

[0114] 4-2 curve

Claims

Claims1. A structure (1) comprising- a nanocrystal (2) configured to convert a primary radiation into a secondary radiation, and- an encapsulation (3) at least partially surrounding the nanocrystal ( 2 ) , wherein the encapsulation comprises a humectant (4) .

2. The structure (1) according to the preceding claim, wherein the nanocrystal (2) comprises a core (21) and at least one shell (22) .

3. The structure (1) according to one of the preceding claims , wherein the humectant (4) is configured for balancing the presence of water.

4. The structure (1) according to one of the preceding claims , wherein the humectant (4) is at least one of salts, small molecules, polymers, xerogels and clay minerals.

5. The structure (1) according to one of the preceding claims , wherein the encapsulation (3) comprises a passivating layer (31) at least partially surrounding the nanocrystal (2) .

6. The structure (1) according to the preceding claim, wherein the passivating layer (31) comprises the humectant(4) .

7. The structure (1) according to the preceding claim,wherein the humectant (4) is embedded in the passivating layer ( 31 ) .

8. The structure (1) according to one of the claims 6 or 7, wherein the humectant (4) is covalently bonded to a material of the passivating layer (31) .

9. The structure (1) according to claim 6, wherein a material of the passivating layer (31) is the humectant ( 4 ) .

10. The structure according to claim 5, wherein the encapsulation comprises a humectant layer (32) abutting the passivating layer (31) , wherein the humectant layer (32) comprises the humectant (4) .

11. The structure according to claim 10, wherein the humectant layer (32) is arranged at least partially between the nanocrystal (2) and the passivating layer ( 31 ) .

12. The structure according to claim 10, wherein the humectant layer (32) at least partially surrounds the passivating layer (31) .

13. The structure according to one of the claims 10 to 12, wherein the encapsulation (3) comprises a plurality of passivating layers (31) and humectant layers (31) arranged in an alternating manner.

14. The structure according to one of the preceding claims, further comprising a barrier layer (5) at least partially surrounding the encapsulation (3) .

15. The structure according to claim 5, wherein the encapsulation (3) comprises a first matrix material (33) , wherein the humectant (4) and the nanocrystal (2) are embedded in the first matrix material (33) .

16. A method for producing a structure (1) , comprising: providing a nanocrystal (2) configured to convert a primary radiation into a secondary radiation, providing an encapsulation (3) at least partially surrounding the nanocrystal (2) , wherein the encapsulation comprises a humectant (4) .

17. The method according to claim 16, wherein providing the encapsulation (3) includes forming a passivating layer (31) at least partially surrounding the nanocrystal ( 2 ) , wherein a material of the passivating layer (31) is the humectant (4) , or wherein the humectant (4) is provided on a surface of the nanocrystal (2) before forming the passivating layer (31) , or wherein the humectant (4) is embedded in the passivating layer (31) during forming the passivating layer (31) , or wherein the humectant (4) is added after forming the passivating layer (31) , or wherein the humectant (4) and the nanocrystal (2) are embedded in a first matrix material (33) .

18. A method for adjusting a water content of a structure (1) according to one of the claims 1 to 15, comprising exposing the structure (1) to an environment of a specific humidity, wherein the humectant (4) releases or absorbs water.

19. An optoelectronic device (1) comprising- a semiconductor chip (11) , in particular a micro-LED, configured to emit a primary radiation, and - a conversion element (12) comprising at least one structure(1) according to one of the claims 1 to 15.

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