WO2021242246A1

WO2021242246A1 - Barrier layer stack provided on a flexible substrate, encapsulated quantum dot structure, method for providing a barrier layer stack on a flexible substrate and method for encapsulating a quantum dot structure

Info

Publication number: WO2021242246A1
Application number: PCT/US2020/034918
Authority: WO
Inventors: Shaopeng ZHU; Rong Wu; Shasha LIU
Original assignee: Applied Materials, Inc.
Priority date: 2020-05-28
Filing date: 2020-05-28
Publication date: 2021-12-02

Abstract

A barrier layer stack provided on a flexible substrate is described. The barrier layer stack comprises at least one organic layer that includes inorganic nanoparticles and at least one inorganic layer.

Description

BARRIER LAYER STACK PROVIDED ON A FLEXIBLE SUBSTRATE, ENCAPSULATED QUANTUM DOT STRUCTURE, METHOD FOR PROVIDING A BARRIER LAYER STACK ON A FLEXIBLE SUBSTRATE AND METHOD FOR ENCAPSULATING A QUANTUM DOT STRUCTURE

TECHNICAL FIELD

[0001 ] Embodiments of the present disclosure relate to a barrier layer stack provided on a flexible substrate, an encapsulated quantum dot structure, a method for providing a barrier layer stack on a flexible substrate, and a method for encapsulating a quantum dot structure.

BACKGROUND

[0002] Barrier films are utilized in applications where materials require very low ingress of moisture and/or oxygen. For instance, barrier films are utilized for television screens, computer monitors, mobile phones, and other devices, etc. for displaying information. In such devices, barrier films can be particularly present together with organic light emitting diodes (OLED). A typical OLED may include layers of organic material situated between two electrodes that are all deposited on a substrate in a manner to form a matrix display panel having pixels that can be individually energized.

[0003] A relatively new type of display technology is the quantum dot (QD) display type. In a QD display type, a quantum dot enhancement film (QDEF) is incorporated in a display. The QDEF is designed to replace the diffuser in a LCD backlight unit (BLU) and is placed between the BLU and the LCD Module (LCM). The QDEF contains red- and green- emitting quantum dots that are tuned to each display system and is illuminated by blue LEDs in the BLU. Quantum dots can provide an alternative for commercial display technology. Quantum dots can support large, flexible displays and would not degrade as readily as OLEDs, making them appropriate candidates for screens such as flat-panel TVs, digital cameras, or mobile phones. [0004] Besides the 30% to 50% less power consumption than LCDs, 50-100 times brighter illumination than cathode ray tube (CRT) displays, better saturated red and green colors, and the use of the same material to generate different colors, QDEFs in a LCD provides less blue-green crosstalk and light absorption in the color filters after the LCD screen, thereby increasing useful light throughput and providing a better color gamut.

[0005] Due to their high sensitivity to moisture and oxygen, quantum dots are typically dispersed in a low moisture and oxygen permeation resin or polymer material and this material is then sandwiched between two barrier films. The barrier films protect the quantum dots in the interior regions of a laminate construction from damage caused by oxygen or water exposure.

[0006] Conventionally, such barrier films are formed of one or more inorganic layers that are deposited on substrates. In many cases, a single inorganic layer is often not enough to realize the barrier effect. For instance, damage in the inorganic layer has been observed under high temperature and/or humidity environments, which is inter alia owed to a high surface roughness of the substrate on which the inorganic layer is deposited. Accordingly, the surface morphology of the substrate on which the inorganic layer is formed influences the barrier performance of the barrier film. For instance, a high surface roughness of the substrate causes the formation of defects in the inorganic layer such as pinholes, which typically propagate through the inorganic layer and lead to an increased Water Vapor Transmission Rate (WVTR).

[0007] In order to reduce such detrimental defects, there have recently been proposed barrier films comprising an inorganic layer and a planarization layer deposited on a substrate. Accordingly, a planarization layer is first deposited on a substrate followed by an inorganic layer deposited on the planarization layer. The planarization layer can eliminate the unevenness or roughness of the surface of the substrate. The surface roughness of the planarization layer should also be as low as possible in order to provide low defect density in the inorganic layer since surface roughness can generally lead to growth of nodules, which can be a reason for defects also in the inorganic layer. Therefore, by smoothing the substrate’s surface, and by having a low surface roughness, the planarization layer can reduce the number of defects in the inorganic layer. However, as the surface roughness of the planarization layer decreases, also the adhesion to the inorganic layer decreases. This creates a dilemma. Therefore, a desirable planarization layer for a barrier film has a low surface roughness and, at the same time, offers a high adhesion to the inorganic layer. These desirable requirements to the planarization layer are difficult to be met and, therefore, so far, only a very limited number of materials can be used as planarization layers which provide moderate results.

[0008] In view of the above, further improvements for barrier films are desired. There is particularly a need for a barrier layer stack on a flexible substrate that exhibits enhanced barrier performance and has an improved structural integrity. There is a further need for methods for providing such a barrier layer stack on a flexible substrate.

SUMMARY

[0009] In light of the above, a barrier layer stack provided on a flexible substrate, an encapsulated quantum dot structure, a method for providing a barrier layer stack on a flexible substrate, and a method for encapsulating a quantum dot structure are provided. Further aspects, advantages, and features of the present disclosure are apparent from the description, and the accompanying drawings.

[0010] According to one embodiment, a barrier layer stack provided on a flexible substrate is provided. The barrier layer stack comprises at least one organic layer including inorganic nanoparticles followed by at least one inorganic layer.

[0011] According to a further embodiment, an encapsulated quantum dot structure is provided. The encapsulated quantum dot structure includes a first barrier layer stack provided on a first substrate and a second barrier layer stack provided on a second substrate, wherein the first barrier layer stack provided on the first substrate comprises a first organic layer comprising inorganic nanoparticles followed by a first inorganic layer. A quantum dot enhancement film containing quantum dots is laminated directly on the first barrier layer stack, particularly on the first inorganic layer.

[0012] According to another embodiment, a method for providing a barrier layer stack on a flexible substrate is provided. The method for providing a barrier layer stack on a flexible substrate includes providing a flexible substrate, providing at least one organic layer comprising inorganic nanoparticles on the flexible substrate, and depositing at least one inorganic layer on the at least one organic layer. [0013] According to a yet another embodiment, a method for encapsulating a quantum dot structure is provided. The method includes providing a first barrier layer stack on a first flexible substrate, laminating a quantum dot enhancement film containing quantum dots over the first barrier layer stack to form a laminate comprising a quantum dot enhancement film containing quantum dots on the first barrier layer stack, providing a second barrier layer stack on a second flexible substrate, and encapsulating the quantum dot enhancement film between the first barrier layer stack and the second barrier layer stack. The first and/or the second barrier layer stack may comprise at least one organic layer including inorganic nanoparticles.

BRIEF DESCRIPTION OF THE DRAWINGS

[0014] So that the manner in which the above recited features of the present disclosure can be understood in detail, a more particular description of the disclosure, briefly summarized above, may be had by reference to embodiments. The accompanying drawings relate to embodiments of the disclosure and are described in the following:

FIG. 1 shows a cross-sectional view of a barrier layer stack provided on a flexible substrate according to embodiments described herein;

FIG. 2 shows an enlarged cross-sectional view of a barrier layer stack provided on a flexible substrate according to embodiments described herein;

FIG. 3 shows an enlarged cross-sectional view of a core-shell nanoparticle according to embodiments described herein;

FIGS. 4 and 5 show a cross-sectional view of a barrier layer stack provided on a flexible substrate according to further embodiments described herein;

FIG. 6 shows a cross-sectional view of an encapsulated quantum dot structure according to embodiments described herein; and FIG. 7 shows a flow chart illustrating a method for providing a barrier layer on a flexible substrate according to embodiments described herein.

DETAILED DESCRIPTION

[0015] Reference will now be made in detail to the various embodiments of the disclosure, one or more examples of which are illustrated in the figures. Within the following description of the drawings, the same reference numbers refer to same components. Generally, only the differences with respect to individual embodiments are described. Each example is provided by way of explanation of the disclosure and is not meant as a limitation of the disclosure. Further, features illustrated or described as part of one embodiment can be used on or in conjunction with other embodiments to yield yet a further embodiment. It is intended that the description includes such modifications and variations.

[0016] Barrier layer stacks, e.g. barrier layer stacks comprising an organic layer and an inorganic layer, can be used in optical applications (for instance, protection of a quantum dot enhancement film (QDEF) from moisture), but the group of materials that are both suitable to form the organic layer and show a sufficient adhesion to the adjacent inorganic layer is very limited. There is thus still a need for improving the adhesion between the organic layer and the inorganic layer in such barrier stack layers. The present disclosure overcomes this drawback by providing a barrier layer stack comprising at least one organic layer comprising inorganic nanoparticles, followed by at least one inorganic layer. The barrier layer stack according to embodiments described herein can show a strong adhesion between an organic layer and an inorganic layer in the barrier layer stack, consequently resulting in an improved integrity of the whole stack. Further, the barrier layer stack described herein provides a good water vapor barrier (e.g., a low water vapor transmission rate, WVTR) and a good stability under high temperature and/or humidity environments.

[0017] The term “barrier layer stack” as used herein refers to a group of layers that provide a barrier against at least one of oxygen or water vapor. Barrier layer stacks as described herein can be flexible and/or transparent. The term “dispersed” may be understood as a state in which particles, particularly nanoparticles, may be homogenously distributed or spread in an organic layer. The term “agglomerate” may be understood as a state in which particles, particularly nanoparticles, may be held together by weak physical interactions ultimately leading to at least a group of particles, particularly a group of nanoparticles, in a specific region of a layer, e.g., the organic layer. The term “organic layer” may be understood as a layer made of an organic material that fills recessed features formed in a substrate surface and/or overcoat a top surface of raised fea tures formed on a substra te surface Further, the term “organic layer” may refer to a layer that levels or flattens (in terms of planarization) the surface of a substrate, in particular a flexible substrate. The term “organic layer material” may refer to a material composition that forms an organic layer. Further, in some embodiments, the term “organic layer material” may refer to a material composition that is applied to a substrate surface and forms an organic layer. When reference is made to the terms “on”, “over”, or “followed by”, i.e. one layer being followed by the other, it is understood that the terms “on”, “over”, or “followed by” are used to define an order of layers, layer stacks, and/or films wherein the starting point is the substrate. This is irrespective of whether the barrier layer stack is depicted upside down or not.

[0018] The terms “substrate” or “flexible substrate” as used herein can particularly embrace flexible substrates such as a web or a foil. The term “substantially inflexible” is understood to distinguish over “flexible”. Specifically, a substantially inflexible substrate can have a certain degree of flexibility, e.g. a glass plate having a thickness of 0.9 mm or below, such as 0.5 mm or below, wherein the flexibility of the substantially inflexible substrate is small in comparison to the flexible substrates. The term “flexible” may also refer to being capable of being formed into a roll.

[0019] It is noted here that a flexible substrate or web as used within the embodiments described herein can typically be characterized in that the flexible substrate is bendable. The term “web” may be synonymously used with the term “strip”, the term “tape”, or the term “flexible substrate”. For example, the web, as described in embodiments herein, may be a foil or another flexible substrate. However, as described in more detail herein, the benefits of embodiments described herein may also be provided for non-flexible substrates or carriers of other inline deposition systems. Yet, it is understood that particular benefit can be utilized for flexible substrates and applications for manufacturing devices on flexible substrates. [0020] According to an embodiment of the present disclosure, and as e.g., illustrated in Fig. 1, a barrier layer stack 110 is provided on a substrate 120, typically on a flexible substrate 120. According to some embodiments, the barrier layer stack 110 of the present embodiments is constituted by a number of layers provided (e.g. by deposition or by coating) one atop of another. The barrier layer stack 110 provided on a flexible substrate 120 may comprise at least one organic layer 130 followed by at least one inorganic layer 140. In some embodiments, the at least one organic layer 130 is provided (e.g. by coating) on the flexible substrate 120. According to further embodiments, the at least one inorganic layer 140 is provided (e.g. by deposition) on the at least one organic layer 130. The barrier layer stack 110 provided on a flexible substrate 120 may have a thickness of 220 nm or above, particularly 500 nm or above, and more particularly 1000 nm or above. According to another embodiment, particularly in embodiments wherein the barrier layer stack 110 provided on a flexible substrate 120 comprises an organic layer 130 followed by an inorganic layer 140, the barrier layer stack 110 provided on a flexible substrate 120 may have a thickness of 10200 nm or below, particularly 5000 nm or below, and more particularly 2000 nm or below. According to yet a further embodiment, particularly in embodiments wherein the barrier layer stack 110 provided on a flexible substrate 120 comprises an organic layer 130 followed by an inorganic layer 140, the barrier layer stack 110 provided on a flexible substrate 120 may have a thickness of 220 nm or above and of 10200 nm or below, particularly a thickness of 500 nm or above and of 5000 nm or below, and more particularly a thickness of 1000 nm or above and of 2000 nm or below.

[0021] In some embodiments, which can be combined with other embodiments described herein, the flexible substrate 120 may include a polymer material selected from the group including polycarbonate (PC), polyethylene terephthalate (PET), poly(methacrylic acid methyl ester) (PMMA), triacetyl cellulose (TAC), cyclo olefin polymer (COP), polyethylene naphthalate) (PEN), and combinations thereof. As an example, the substrate may include polyethylene terephthalate (PET). Other most suitable polymer materials for the substrate include PEN and/or PC. The surface of the flexible substrate 120 onto which the at least one organic layer 130 is provided, e.g. coated or otherwise joined, and/or the surface of the at least one organic layer 130 onto which the at least one inorganic layer 140 is provided can be treated to improve adhesion. Useful surface treatments include electrical discharge in the presence of a suitable reactive or non-reactive atmosphere (e.g., plasma, glow discharge, corona discharge, dielectric barrier discharge or atmospheric pressure discharge); chemical pretreatment; or flame pretreatment.

[0022] According to embodiments of the present disclosure, the at least one inorganic layer 140 may comprise a material selected from the group consisting of metal oxides, metal nitrides, metal carbides, metal oxynitrides, metal oxyborides, and combinations thereof. According to further embodiments, the at least one inorganic layer 140 may comprise a material selected from the group consisting of titanium oxides, indium oxides, tin oxides, indium tin oxide (ITO), tantalum oxide, and combinations thereof. In some embodiments, the at least one inorganic layer 140 may comprise a material selected from the group consisting of boron carbide, tungsten carbide, silicon carbide, aluminum nitride, boron nitride, aluminum oxynitride, silicon oxynitride, boron oxynitride, zirconium oxyboride, titanium oxyboride, and combinations thereof. In some embodiments, the at least one inorganic layer 140 may comprise a material selected from the group consisting of Si0₂, Ti0₂, A1₂0₃, Nb₂0₅, Si₃N₄, Zr0₂, HfO_x, and combinations thereof.

[0023] In some embodiments, the at least one inorganic layer 140 may have a thickness of 1 nm or above, particularly 20 nm or above, and more particularly 50 nm or above. According to another embodiment, the at least one inorganic layer 140 may have a thickness of 200 nm or below, particularly 150 nm or below, and more particularly 100 nm or below. According to yet a further embodiment, the at least one inorganic layer 140 may have a thickness of 1 nm or above and of 200 nm or below, particularly a thickness of 20 nm or above and of 150 nm or below, and more particularly a thickness of 50 nm or above and of 100 nm or below. The at least one inorganic layer 140 is typically sufficiently thick so as to be continuous, and sufficiently thin so as to ensure that the desired Water Vapor Transmission Rate (WVTR) and/or Oxygen Transmission Rate (OTR) is achieved.

[0024] The barrier layer stack 110 provided on a flexible substrate 120 and/or the at least one inorganic layer 140 is particularly beneficial for reducing WVTR (in units of g per cm² and day) and/or OTR. In some embodiments, WVTR of the barrier layer stack 110 provided on a flexible substrate 120 can be less than 10^'1 g/m²/day, and particularly about 10^' ³ to 10^'2 g/m²/day. [0025] A common method to quantify WVTR is the test method ASTM F1249-13 “Standard Test Method for Water Vapor Transmission Rate Through Plastic Film and Sheeting Using a Modulated Infrared Sensor”. The test method ASTM F1249-13 is suitable for testing flexible barrier films and sheets consisting of single and multilayer natural or synthetic polymers and foils. The test method ASTM F1249-13 relies on instrumentation provided by MOCON Permatran-W® analyzers.

[0026] In some embodiments, the at least one inorganic layer 140 may be provided (e.g. deposited) on the at least one organic layer 130. According to another embodiment, the at least one inorganic layer 140 may be provided (e.g. deposited) on the at least one organic layer 130 by physical vapor deposition (PVD), for example sputtering or evaporation, or chemical vapor deposition (CVD).

[0027] In some embodiments, the at least one organic layer 130 may have a thickness of 200 nm or above, particularly 500 nm or above, and more particularly 1000 nm or above. According to another embodiment, the at least one organic layer 130 may have a thickness of 10000 nm or below, particularly 5000 nm or below, and more particularly 2000 nm or below. According to yet a further embodiment, the at least one organic layer 130 may have a thickness of 200 nm or above and of 10000 nm or below, particularly a thickness of 500 nm or above and of 5000 nm or below, and more particularly a thickness of 1000 nm or above and of 2000 nm or below. The thickness of the at least one organic layer 130 may depend on the surface roughness of the flexible substrate 120. The thickness of the at least one organic layer 130 will particularly be sufficient to provide a smooth, defect-free surface to which at least one inorganic layer 140 can be provided (e.g. deposited) subsequently.

[0028] According to some embodiments, the at least one organic layer 130 can he provided (e.g. coated or applied) by using any suitable technique. For instance, the at least one organic layer 130 may be provided on the flexible substrate 120 by using a coating method, and particularly by a solution coating method, particularly selected from the group consisting of gravure coating, flow coating, curtain coating, dip coating, spray coating, and combination thereof. The at least one organic layer 130 can also be provided by applying an organic layer material containing monomers, oligomers and/or a polymer, particularly at least one cross- linkable polymer, and inorganic nanoparticles in solvent and then removing the solvent using conventional techniques (e.g., at least one of heat or vacuum). In some embodiments, removing the solvent using conventional techniques may be followed by crosslinking, for example, using an electron beam apparatus, UV light source, electrical discharge apparatus or another suitable device. Suitable organic layer materials can typically remain liquid or have sufficiently low viscosity after solvent evaporation at elevated temperatures to self-level over the features, without being tacky when cooled to room temperature. Further, the at least one organic layer 130 can have a sufficiently high degradation temperature to remain stable during subsequent processing (e.g. providing at least an inorganic layer 140), which can involve extreme temperatures .

[0029] In some embodiments, the organic layer material forming the at least one organic layer 130 can be subjected to one or more additional heating stages to allow further reflow of the composition into and over features, e.g., features of a substrate, after solvent evaporation. Such additional heating stages can be particularly carried out at temperatures above the initial heating temperature, for example, from about 60 °C to about 350 °C, and particularly from about 60 °C to about 100° C.

[0030] In some embodiments, the organic layer material can also be cured or crossiinked via exposure to light (e.g., DUV, i-line, g-line, and/or broad band) in addition to, or in lieu of, heating. The conditions for forming the at least one organic layer 130 can depend upon the particular organic layer material used, and may result in a dried, cured, and/or crossiinked organic layer.

[0031] According to some embodiments, the aforementioned process for providing at least one organic layer can be repeated to provide multiple organic layers over a substrate, particularly a flexible substrate. Multiple organic layers may be necessary to fill recessed features formed in a substrate surface and/or overcoat a top surface of raised features formed on a substrate surface. In some embodiments, no etching (wet or dry), contact planarization, or polishing of an organic layer may be necessary to fill recessed features formed in a substrate surface and/or overcoat a top surface of raised features formed on a substrate surface.

[0032] In some embodiments, the at least one organic layer 130 provided on the flexible substrate 120 and/or the organic layer material may comprise at least one cross-linkable polymer, particularly selected from the group consisting of a polyacrylic resin, an acrylic- urethane resin, an epoxy acrylic resin, a melamine resin, an amino resin, a polyurethane resin, a polyester resin, a polysiloxane resin, and combinations thereof. According to further embodiments, the at least one organic layer 130 provided on the flexible substrate 120 and/or the organic layer material may comprise monomers, particularly selected from the group consisting of urethane acrylates, isobornyl acrylate, dipentaerythritol pentaacrylates, epoxy acrylates blended with styrene, di-trimethylolpropane tetraacrylates, diethylene glycol diacrylates, 1,3-butylene glycol diacrylate, pentaacrylate esters, pentaerythritol tetraacrylates, pentaerythritol triacrylates, ethoxylated (3) trimethylolpropane triacrylates, ethoxylated (3) trimethylolpropane triacrylates, alkoxylated trifunctional acrylate esters, dipropylene glycol diacrylates, neopentyl glycol diacrylates, ethoxylated (4) bisphenol a dimethacrylates, cyclohexane dimethanol diacrylate esters, isobornyl methacrylate, cyclic diacrylates, and tris(2 -hydroxy ethyl) isocyanurate triacrylate, acrylates of the foregoing methacrylates, and methacrylates of the foregoing acrylates. The at least one organic layer 130 provided on the flexible substrate 120 and/or the organic layer material may also comprise monomers, particularly selected from the group consisting of vinyl ethers, vinyl naphthylene, acrylonitrile, and mixtures thereof, and/or acrylate oligomers.

[0033] In some embodiments, the at least one organic layer 130 provided on the flexible substrate 120 and/or the organic layer material may additionally comprise at least one organic solvent. According to further embodiments, the at least one organic layer 130 provided on the flexible substrate 120 and/or the organic layer material may additionally comprise at least one additive, such as cross-linkers and catalysts, e.g. photo-initiators.

[0034] According to some embodiments, which can be combined with other embodiments herein, the at least one inorganic layer 140 may be directly in contact with the at least one organic layer 130. Similarly, at least one organic layer 130 may be directly in contact with a substrate, particularly a flexible substrate 120. In some embodiments, no further layers or films are present between the at least one inorganic layer 140 and the at least one organic layer 130 and/or the at least one organic layer 130 and the flexible substrate 120. Fig. 2 shows an enlarged cross-sectional view of a barrier layer stack 210 provided on a flexible substrate 220 according to embodiments described herein.

[0035] According to embodiments which can be combined with other embodiments herein, the at least one organic layer 230 may further comprise inorganic nanoparticles, particularly inorganic nanoparticles 250. [0036] In some embodiments, the inorganic nanoparticles 250 of the at least one organic layer 230 may comprise (or may even consist of) a material selected from the group consisting of inorganic oxide, nitride, carbide, sulfide, selenide, carbonate, phosphate, and sulphate, and particularly an inorganic oxide. According to further embodiments, the inorganic nanoparticles 250 of the at least one organic layer 230 may comprise (or may even consist of) a material selected from the group consisting of Si0₂, silicon carbide, silicon nitride, cerium dioxide, Nb₂O₅, Ta₂O ₅ alumina, titania, zirconia, tin oxide, zinc oxide, silicon oxide- coated Ti0₂, Sb-Sn0₂, Fe₂0₃, magnetite, IndiumTinOxide (ITO)), antimony -doped tin oxide (AΊΌ), indium oxide, antimony oxide, fluorine-doped tin oxide, phosphorous- doped tin oxide, zinc antimonite, indium doped zinc oxide, and combinations thereof.

[0037] Inorganic nanoparticles can be manufactured by various procedures. For example, Park et al. present a method for the production of alumina nanoparticles from Al(OC₃H₇)₃ (Park et al., Materials Research Bulletin 40, p. 1506-1512, 2005). Also, the manufacture of Si0₂ nanopartides can be performed according to methods known in the art. For example, the manufacture of Si0₂ nanopartides can be performed e.g. by the process described by Stober et al. (Stober et al., Journal of Colloid and Interface Science 26, p. 62-69, 1968) and as described by patent application PCT/EP 2012/074433. Si0₂ nanopartides can also be purchased commercially, e g. from Sigma-Aldrich®. Zinc oxide nanopartides, in particular Zinc (II) oxide nanopartides can be produced from metallic zinc or zinc ores by vaporisation in the presence of oxygen, or from zinc carbonates or zinc hydroxides by calcination. Zirconia nanopartides can be fabricated from zirconium silicate by calcination. In addition, titania nanopartides can be manufactured according to Peng et al. starting with Ti( S0₄)₂ (Peng et al,, Journal of Physical Chemistry B 109, p. 4947-4952, 2005),

[0038] According to some embodiments, the inorganic nanoparticles 250 of the at least one organic layer 230 may have functional groups on their surface. In some embodiments, the functional groups of the inorganic nanopartides may form chemical bonds to the inorganic layer at the interface between the at least one organic layer and the at least one inorganic layer. The functional groups on the surface of the inorganic nanopartides 250 are particularly suitable for chemically binding (e.g., by a covalent bond) the inorganic layer 240. For instance, hydroxyl groups on the surface of Si0₂ nanopartides 250 are suitable for chemically binding an inorganic layer comprising Si0₂. Fig. 2 illustrates the final covalent bonds between such inorganic nanPaki2033. 250 and the inorganic layer 240 via dehydration of hydroxyl groups, consequently forming Si-O-Si groups which bind the inorganic nanoparticles 250 to the inorganic layer 240 together. As a result thereof, the organic layer 230 strongly adheres to the inorganic layer 240. The provision of chemical bonds between the organic layer 230 and the inorganic layer 240 can guarantee an improved adhesion between both layers 230 and 240, which can result in an increased integrity of the whole barrier layer stack. Since the organic layer 230 can also function as a planarization layer that eliminates the unevenness or roughness of the substrate surface, a desirably low WVTR is also achieved. In other words, the provision of functional groups on the surface of the inorganic nanoparticles 250 may result in both a desirably low WVTR and a good adhesion between the organic layer 230 and the inorganic layer 240. The provision of functional groups on the surface of the inorganic nanoparticles 250 may further enable using an organic layer 230 having a very low surface roughness, consequently leading to an even further improved WVTR.

[0039] In some embodiments, the functional groups on the surface of the inorganic nanoparticles 250 may comprise reactive oxygen groups and/or reactive amino groups. For example, the reactive oxygen groups may be hydroxyl, carboxyl, ether, and/or ester. Particularly, the reactive oxygen groups may be hydroxyl and/or carboxyl. The reactive amino groups may be primary amines, secondary amines and/or tertiary amines.

[0040] In some embodiments, the functional groups may also comprise at least a functional group selected from the group consisting of an amino, carbonyl, carboxyl, ester, ether, epoxy, hydroxyl, acrylic, methacrylic, anhydride, acid halide, halogen, allyl, vinyl, styrene, aryl, acetylene, azide, ureido group; 5 to 6 membered heterocyclic hydrocarbon groups containing from 1 to 3 nitrogen atoms; isonicotinamidyl, bi-pyridyl, nitrile, isonitrile, mercapto, sulfide, sulfonic acid, sulfmic acid, thiosulfonic acid, and thiocyanate.

[0041 ] In some embodiments, the inorganic nanoparticles 250 of the at least one organic layer 230 may be dispersed in the at least one organic layer 230. According to further embodiments, the inorganic nanoparticles 250 of the at least one organic layer 230 may be agglomerated in the at least one organic layer 230, particularly, agglomerated close to the surface of the at least one organic layer 230 on which the at least one inorganic layer 240 is provided. [0042] Fig. 3 shows an enlarged cross-sectional view of an inorganic nanoparticle 350 according to embodiments described herein. In this example, the inorganic nanoparticle 350 may comprise a core 352 and a shell 354. The core 352 and/or the shell 354 may comprise different materials. The core 352 may comprise a material as described herein as material suitable to be used for the nanoparticles 250. For instance, the core 352 may comprise a material selected from the group consisting of Si0₂, silicon carbide, silicon nitride, cerium dioxide, Nb₂0₅, Ta₂0₅, alumina, titania, zirconia, tin oxide, zinc oxide, silicon oxide- coated Ti0₂, Sb-Sn0₂, Fe₂0₃, magnetite, IndiumT inOxide (ITO), antimony-doped tin oxide (ATO), indium oxide, antimony oxide, fluorine-doped tin oxide, phosphorous- doped tin oxide, zinc antimonite, indium doped zinc oxide, and combinations thereof. According to further embodiments, the core 352 may comprise a material selected from the group consisting of inorganic oxide, nitride, carbide, sulfide, selenide, carbonate, phosphate, and sulphate. Particularly, the core 352 may comprise an inorganic oxide.

[0043] In some embodiments, the shell 354 of the inorganic nanoparticle 350 may comprise a material as defined above for the core 352. According to further embodiments, the core 352 and the shell 354 may comprise the same or different materials. The shell 354 has an outer surface. In some embodiments, the shell 354 may have the functional groups as described herein on the outer surface. As discussed above, the functional groups on the outer surface of the shell 354 may be suitable for chemically binding an inorganic layer. [0044] In some embodiments, the shell 354 may comprise at least one attachment group bearing a functional group suitable for binding to an inorganic layer. The at least one attachment group may have the general Formula: B - L - FG, wherein B is a binding group, L is a linking group, and FG is a functional group on the outer surface of the shell 354. The binding group B represents, for example, -Si(R)(R²)-, wherein R and R² independently of each other represent alkoxy groups having from 1 to 12 carbon atoms, alkyl groups having from 1 to 12 carbon atoms, halogen atoms, and/or a bond to oxygen atoms originating from the inorganic nanoparticles 250 and/or further attachment groups; or -CH2R³-, -C(=0)-NH-, -C(=0)-0-, unsubstituted or substituted aryl, wherein R³ represents - CH(0H)-CH₂-0", -CH(OH)-CH₂-; a linear, unsubstituted or substituted hydrocarbon group having from 1 to 5 carbon atoms.

[0045] The linking group L represents a linear, unsubstituted or substituted hydrocarbon group having from 1 to 20 carbon atoms; a cyclic, unsubstituted or substituted hydrocarbon group having from 3 to 8 carbon atoms; the linear or cyclic hydrocarbon group interrupted by one or more oxygen atoms and/or nitrogen atoms; the linear or cyclic hydrocarbon group having one or more double and/or triple bonds; unsubstituted or substituted aryl or heteroaryl, phosphonates, and bipyridyl. [0046] Forms of binding the at least one attachment group to inorganic nanoparticles are known in the art. The binding of the at least one attachment group, e.g. at least one functional group, to inorganic nanoparticles is also called functionalization of the nanoparticles. Particularly, binding of the at least one attachment group to a Si0₂ nanoparticle is believed to consist of a hydrolysis process and a condensation process. During the hydrolysis process, alkoxy groups of tetraalkyl silicate are hydrolysed to give the corresponding silanol. During the condensation process, hydroxy groups of different silanol molecules condensate and thus build up a Si0₂ structure.

[0047] The size (e.g., dimensions) of the inorganic nanoparticles 250 and 350 described herein (with or without the functional groups and/or the core-shell structure as described herein) can be determined by dynamic light scattering, disc centrifugation, nanoparticle tracking analysis, tunable resistive pulse sensing, atomic force microscopy, and/or electron microscopy. These methods for determining the particle size distribution are known in the art. Particularly, the size of the inorganic nanoparticles 250 and 350 of the at least one organic layer 230 can be determined by dynamic light scattering according to ISO 13320:2020, e.g., Particle size analysis — Laser diffraction methods. This norm considers the nanoparticles as being spherical and, therefore, nanoparticle size is reported as a volume equivalent sphere diameter.

[0048] In some embodiments, the inorganic nanoparticles may have a D10 particle diameter of 5 nm to 150 nm, particularly 5 nm to 60 nm, more particularly 10 nm to 50 nm. According to further embodiments, the inorganic nanoparticles 250 of the at least one organic layer 230 may have a D50 particle diameter of 1 nm to 150 nm, particularly 5 nm to 60 nm, more particularly 10 nm to 50 nm. Yet, according to some embodiments, the inorganic nanopartides 250 of the at least one organic layer 230 may have a D90 particle diameter of 5 nm to 150 nm, particularly 5 nm to 60 nm, more particularly 10 nm to 50 nm. The foregoing particle diameters concern the nanopartides 250 and 350 that are used in the at least one organic layer as described herein with or without the functional groups and/or the core-shell structure as described herein. For instance, in the event that the inorganic nanopartides 250 and 350 described herein comprise a functional group on their surface, the aforementioned particle diameters refer to the combination of the inorganic nanopartides and the functional group. Further, in the event that the inorganic nanopartides 350 described herein comprise a core 352 and a shell 354, the aforementioned particle diameters refer to the combination of the core 352 and the shell 354.

[0049] The term “D10” refers to the particle diameter in a particle size distribution, wherein 10% of the particles in the particle size distribution have a lower particle diameter and 90% of the particles in the particle size distribution have a higher particle diameter. The term “D50” refers to the particle diameter in a particle size distribution, wherein 50% of the particles in the particle size distribution have a lower particle diameter and 50% of the particles in the particle size distribution have a higher particle diameter. The term “D50” is also known as the median diameter. The term “D90” refers to the particle diameter in a particle size distribution, wherein 90% of the particles in the particle size distribution have a lower particle diameter and 10% of the particles in the particle size distribution have a higher particle diameter.

[0050] Figs. 4 and 5 show cross-sectional views of a barrier layer stack provided on a flexible substrate according to further embodiments described herein. Particularly, Fig. 4 illustrates a cross-sectional view of a barrier layer stack 410 provided on a flexible substrate 420 according to embodiments described herein. The barrier layer stack 410 may compromise an organic layer 430 comprising inorganic nanoparticles followed by an inorganic layer 440. According to some embodiments, which can be combined with other embodiments herein, the barrier layer stack 410 or 510 may comprise further layers. In some embodiments, an additional layer 422 may be provided between an organic layer 430 and a substrate 420, in particular, a flexible substrate 420. For instance, a separate adhesion promotion layer may be provided between an organic layer 430 and a flexible substrate 420. The adhesion promotion layer can be, for example, a separate polymeric layer or a metal-containing layer such as a layer of metal, metal oxide, metal nitride or metal oxynitride. The adhesion promotion layer may have a thickness of a few nanometers (nm) (e.g., 1 or 2 nm) to about 50 nm or more.

[0051] Fig. 5 illustrates a cross-sectional view of a barrier layer stack 510 provided on a flexible substrate 520 according to embodiments described herein. In some embodiments, an additional layer 544 may be provided on an inorganic layer 542. For example, the additional layer 544 may be an additional inorganic layer 544 provided on the at least one inorganic layer 542. The additional inorganic layer 544 may comprise a material similar to those described above for an inorganic layer. According to further embodiments, the barrier layer stack 510 may comprise at least one organic layer 530 comprising inorganic nanoparticles followed by an inorganic layer 542 deposited by atomic layer deposition, which is followed by an additional inorganic layer 544 deposited by plasma-enhanced chemical vapor deposition (PECVD). The additional inorganic layer 544 deposited by PECVD may comprise SiN_x or Si0₂.

[0052] According to further embodiments, an encapsulated quantum dot structure is provided. As illustrated in Fig. 6., an encapsulated quantum dot structure 600 as described herein can have the following architecture: first flexible substrate 620/first barrier layer stack 610/QDs 650/second barrier layer stack 6107second flexible substrate 620’ as illustrated in Fig. 6. An encapsulated quantum dot structure 600 can be an encapsulated quantum dot enhancement film QDEF. The encapsulated quantum dot structure 600 can include a first barrier layer stack 610 provided on a first substrate 620 and a second barrier layer stack 610’ provided on a second substrate 620’. The substrate can be PET or can be any flexible substrate as described above. The first barrier layer stack 610 provided on a first substrate 620 can be a barrier layer stack as described above, and can e.g., comprise a first organic layer 630 comprising inorganic nanoparticles followed by a first inorganic layer 640. On this first barrier layer stack 610, particularly on the first inorganic layer 640, a quantum dot enhancement film 660 containing quantum dots 650 can be laminated directly. Thereafter, a second barrier layer stack 610’ provided on a second substrate 620’ can be laminated. The second barrier layer stack 610’ provided on the second substrate 620’ can be a barrier layer stack as described above, and can e.g., comprise a second organic layer 630’ comprising inorganic nanoparticles followed by a second inorganic layer 640’. The second inorganic layer 640’ of the second barrier layer stack 610’ faces the QDs 650. Although in the present example of Fig. 6 an encapsulated quantum dot structure 600 comprising barrier layer stacks comprising one organic layer comprising inorganic nanoparticles followed by one inorganic layer are illustrated, the present embodiments are not limited thereto. Any additional number of layers can be arranged, as for instance described above with reference to figs. 4 and 5.

[0053] Fig. 7 shows a flow chart illustrating a method 700 for providing a barrier layer stack on a substrate (e.g., a flexible substrate) according to embodiments described herein. According to an aspect of the present disclosure, the method 700 may include providing a substrate, particularly a flexible substrate (block 701). According to embodiments described herein, the method 700 may further include providing at least one organic layer comprising inorganic nanoparticles on the substrate, particularly the flexible substrate (block 702). According to further embodiments, the method 700 may further include depositing at least one inorganic layer on the at least one organic layer comprising inorganic nanoparticles (block 703). The barrier layer stack and the substrate can be those described above.

[0054] In some embodiments, providing a flexible substrate may include continuously transporting a flexible substrate from an unwinding roller to a re-winding roller. According to further embodiments, providing at least one organic layer comprising inorganic nanoparticles on a flexible substrate may include preparing an organic layer material by mixing inorganic nanoparticles and at least one of the materials selected from the group consisting of at least one cross-linkable polymer, oligomers, monomers, organic solvent, and additives. According to further embodiments, providing at least one organic layer comprising inorganic nanoparticles on a flexible substrate may include coating an organic layer material comprising at least one of the materials selected from the group consisting of at least one cross-linkable polymer, oligomers, monomers, organic solvent, additives, and inorganic nanoparticles on a flexible substrate by using a method selected from the group consisting of gravure coating, flow coating, curtain coating, dip coating, spray coating and combinations thereof. In some embodiments, providing at least one organic layer comprising inorganic nanoparticles on a flexible substrate may further include providing an additional layer (e.g. a separate adhesion promotion layer) between an organic layer comprising inorganic nanoparticles and a flexible substrate.

[0055] According to further embodiments, providing at least one organic layer comprising inorganic nanoparticles on a flexible substrate may further include pretreating nanoparticles to form pretreated nanoparticles having functional groups on their outer surface. In some embodiments, the inorganic nanoparticles of the at least one organic layer may be pretreated nanoparticles having functional groups on their outer surface. According to further embodiments, the pretreated nanoparticles having functional groups on their surface may be formed by grafting functional groups on the outer surface of the nanoparticle, in-situ formation of functional groups on the outer surface of the nanoparticle, forming a shell having functional groups on the outer surface of the nanoparticle, encapsulating at least part of the outer surface of the nanoparticle, and combinations thereof. In some embodiments, the functional groups of the pretreated nanoparticles may form chemical bonds to the inorganic layer at the interface between the organic layer and the inorganic layer.

[0056] FIG. 8 shows a flow chart illustrating a method 800 for encapsulating a quantum dot structure according to embodiments described herein. According to an aspect of the present disclosure, the method 800 may include providing a first barrier layer stack on a first substrate (block 801). Particularly, the first barrier layer stack on a first substrate may comprise at least one organic layer comprising inorganic nanoparticles followed by at least one inorganic layer. In some embodiments, providing a substrate may include continuously transporting a substrate. According to embodiments described herein, the method 700 may further include laminating a quantum dot enhancement film containing quantum dots over the first barrier layer stack to form a laminate comprising a quantum dot enhancement film containing quantum dots on the first barrier layer stack (block 802). The first barrier layer stack and the substrate can be those described above. In some embodiments, laminating a quantum dot enhancement film containing quantum dots over the first barrier layer stack may comprise at least one of preparing a mixture of a polymer material and quantum dots and forming a quantum dot enhancement film containing quantum dots from a mixture of a polymer material and quantum dots.

[0057] According to some embodiments, the method 800 may further include providing a second barrier layer stack on a second substrate (block 803). Particularly, the second barrier layer stack on a second substrate may comprise at least one organic layer comprising inorganic nanoparticles followed by at least one inorganic layer. The second barrier layer stack and the substrate can be those described above. According to further embodiments described herein, the method 800 may further include encapsulating the quantum dot enhancement film between the first barrier layer stack and the second barrier layer stack (block 804). [0058] The present disclosure has several advantages including the provision of an increased number of organic layer materials that are suitable for forming the organic layer, an improvement of the adhesion of an organic layer to an inorganic layer within a barrier stack layer, and a good water vapor barrier and a good stability of a barrier stack layer under high temperature and/or humidity environments.

[0059] While the foregoing is directed to embodiments of the disclosure, other and further embodiments of the disclosure may be devised without departing from the basic scope thereof, and the scope thereof is determined by the claims that follow.

Claims

1. A barrier layer stack provided on a flexible substrate, the barrier layer stack comprising at least one organic layer comprising inorganic nanoparticles followed by at least one inorganic layer.

2. The barrier layer stack according to claim 1, wherein the inorganic nanoparticles of the at least one organic layer have functional groups on their surface.

3. The barrier layer stack according to claim 2, wherein the functional groups of the inorganic nanoparticles form chemical bonds to the inorganic layer at the interface between the at least one organic layer and the at least one inorganic layer.

4. The barrier layer stack according to any of the preceding claims, wherein the inorganic nanoparticles have a D50 particle diameter of 1 nm to 150 nm, particularly 5 nm to 60 nm, more particularly 10 nm to 50 nm.

5. The barrier layer stack according to any of the preceding claims, wherein the at least one inorganic layer comprises a material selected from the group consisting of Si0₂, Ti0₂, A1₂0₃, Nb₂0₅, Si₃N₄, Zr0₂, HfO_x, and combinations thereof.

6. The barrier layer stack according to any of the preceding claims, wherein the at least one organic layer provided on the flexible substrate further comprises a cross-linkable polymer, particularly selected from the group consisting of a polyacrylic resin, an acrylic- urethane resin, an epoxy acrylic resin, a melamine resin, an amino resin, a polyurethane resin, a polyester resin, a polysiloxane resin, and combinations thereof.

7. The barrier layer stack according to any of the preceding claims, wherein the at least one organic layer is coated on the flexible substrate by using a solution coating method, particularly selected from the group consisting of gravure coating, flow coating, curtain coating, dip coating, spray coating, and combinations thereof.

8. The barrier layer stack according to any of the preceding claims, wherein the at least one inorganic layer is deposited on the at least one organic layer by physical vapor deposition (PVD) or chemical vapor deposition (CVD).

9. An encapsulated quantum dot structure, the encapsulated quantum dot structure including a first barrier layer stack provided on a first substrate and a second barrier layer stack provided on a second substrate, wherein the first barrier layer stack comprises a first organic layer comprising inorganic nanoparticles followed by a first inorganic layer, and wherein a quantum dot enhancement film containing quantum dots is laminated directly on the first barrier layer stack, particularly on the first inorganic layer.

10. The encapsulated quantum dot structure according to claim 9, wherein the second barrier layer stack comprises a second organic layer comprising organic nanoparticles followed by a second inorganic layer.

11. A method for providing a barrier layer stack on a flexible substrate comprising: providing a flexible substrate; providing at least one organic layer comprising inorganic nanoparticles on the flexible substrate; and depositing at least one inorganic layer on the at least one organic layer.

12. The method according to claim 11, wherein providing the at least one organic layer on the flexible substrate includes coating an organic layer material comprising at least one cross-linkable polymer, oligomers, monomers, organic solvent, additives, and inorganic nanoparticles on the flexible substrate by using a method selected from the group consisting of gravure coating, flow coating, curtain coating, dip coating, spray coating and combinations thereof.

13. The method according to claim 12, wherein the inorganic nanoparticles are pretreated nanoparticles having functional groups on their outer surface, and wherein particularly the pretreated nanoparticles are formed by a method selected from the group of grafting functional groups on the outer surface of the nanoparticle, in-situ formation of functional groups on the outer surface of the nanoparticle, forming a shell having functional groups on the outer surface of the nanoparticle, encapsulating at least part of the outer surface of the nanoparticle, and combinations thereof.

14. The method according to claim 13, wherein the functional groups of the pretreated nanoparticles form chemical bonds to the inorganic layer at the interface between the organic layer and the inorganic layer.

15. A method for encapsulating a quantum dot structure, comprising: providing a first barrier layer stack comprising at least one organic layer that comprises inorganic nanoparticles on a first flexible substrate; laminating a quantum dot enhancement film containing quantum dots over the first barrier layer stack to form a laminate comprising a quantum dot enhancement film containing quantum dots on the first barrier layer stack; and the method particularly further comprising: providing a second barrier layer stack on a second flexible substrate; and encapsulating the quantum dot enhancement film containing quantum dots between the first barrier layer stack and the second barrier layer stack.