Display panel, preparation method thereof and display device

Abstract

The embodiment of the invention provides a display panel, a preparation method thereof and a display device, relates to the technical field of display, and is used for improving the display uniformity and the display effect of the display panel. The display panel comprises a substrate, a first electrode layer, a light-emitting function layer, a second electrode layer and a first covering layer. Wherein the first electrode layer, the light-emitting function layer and the second electrode layer are sequentially arranged on one side of the substrate in a stacked mode in the direction away from the substrate. The light-emitting functional layer comprises a light-emitting layer, and the light-emitting layer comprises a quantum dot material. The first covering layer is located on the side, away from the substrate, of the second electrode layer, and the first covering layer comprises an inorganic material. The display panel is used for displaying images.

Description

Technical Field

[0001] This disclosure relates to the field of display technology, and in particular to a display panel, a method for manufacturing the same, and a display device. Background Technology

[0002] Quantum dots (QDs), as nanoscale semiconductor materials, have their emission wavelength determined by their size. By controlling the size of quantum dots, precise control over the emitted color can be achieved, resulting in advantages such as narrow half-width at half-maximum (WWHM), high color purity, and wide color gamut. QLED (Quantum Dot Light Emitting Diode) display devices, which use quantum dots as light-emitting devices, also achieve better color performance due to the aforementioned characteristics of quantum dot materials. Furthermore, QLED display devices offer advantages such as high energy efficiency, good stability, and long lifespan, and are widely used in various display devices, showing promise as one of the next generation of mainstream display technologies. Summary of the Invention

[0003] The purpose of the embodiments disclosed herein is to provide a display panel and its manufacturing method, as well as a display device, for improving the display uniformity and display effect of the display panel.

[0004] To achieve the above objectives, the embodiments of this disclosure provide the following technical solutions:

[0005] On one hand, a display panel is provided, comprising a substrate, a first electrode layer, a light-emitting functional layer, a second electrode layer, and a first cover layer. The first electrode layer, the light-emitting functional layer, and the second electrode layer are sequentially stacked on one side of the substrate in a direction away from the substrate. The light-emitting functional layer includes a light-emitting layer comprising a quantum dot material. The first cover layer is located on the side of the second electrode layer away from the substrate, and the first cover layer comprises an inorganic material.

[0006] Using inorganic materials as the first cover layer ensures that it does not react with materials used in subsequent processes, such as optical adhesives and / or sealing adhesives. This improves the display uniformity of the display panel, thereby enhancing its display performance. Furthermore, using an inorganic first cover layer can significantly improve the display panel's current density, brightness, current efficiency, and maximum external quantum efficiency without adversely affecting the light emission angle distribution. This improves display uniformity, reduces power consumption, and enhances stability and lifespan, ultimately resulting in a better display experience.

[0007] In some embodiments, the inorganic material is selected from metal oxides.

[0008] In some embodiments, the metal oxide is selected from at least one of molybdenum oxide, tungsten oxide, copper oxide, zinc oxide, aluminum oxide, or vanadium pentoxide.

[0009] There are many types of metal oxides, and a wide range of choices are available. Metal oxides can be selected to meet various requirements such as the manufacturing process, overall compatibility, refractive index, and light emission angle distribution of the display panel, depending on the actual application scenario.

[0010] In some embodiments, the thickness of the first cover layer is 15 nanometers to 25 nanometers.

[0011] The thinner first cover layer not only facilitates greater photon output but also contributes to the thinner and lighter display panel. Furthermore, this thickness is suitable for various colors of luminescent quantum dots, including red, green, and blue luminescent quantum dots.

[0012] In some embodiments, the refractive index of the first cover layer is greater than or equal to 1.8.

[0013] In some embodiments, the display panel further includes a second cover layer located between the second electrode layer and the first cover layer, the second cover layer comprising an organic material.

[0014] In some embodiments, the refractive index of the second cover layer is less than that of the first cover layer.

[0015] By properly setting the refractive indices of the first and second cover layers, the light output angle distribution and current efficiency of the display panel can be significantly improved, thereby enhancing the display effect of the display panel.

[0016] In some embodiments, the refractive index of the first cover layer is 2 and the refractive index of the second cover layer is 1.85.

[0017] In some embodiments, the thickness of the second cover layer is 35 nanometers to 45 nanometers.

[0018] In some embodiments, the material of the second covering layer is selected from at least one of N,N′-bis(1-naphthyl)-N,N′-diphenyl-(1,1′-biphenyl)-4,4′-diamine, tris(4-carbazole-9-ylphenyl)amine, 1,1-bis[(di-4-toluidine)phenyl]cyclohexane, 4,4′-bis(N-carbazole)-1,1′-biphenyl, and 1,3-bis(N-carbazole)benzene.

[0019] In some embodiments, the maximum external quantum efficiency of the display panel is 17%-30%.

[0020] On the other hand, a display device is provided, comprising: a circuit board, and a display panel as described above, the display panel being connected to the circuit board.

[0021] In some embodiments, the display device further includes an encapsulation bezel and an adhesive sealant. The encapsulation bezel is disposed around the display panel. The adhesive sealant is located between the encapsulation bezel and the display panel and is configured to bond the encapsulation bezel and the display panel.

[0022] In another aspect, a method for fabricating a display panel is provided, comprising: sequentially stacking a first electrode layer, a light-emitting functional layer, and a second electrode layer on a substrate. A first capping layer is formed on the side of the second electrode layer away from the substrate, the first capping layer comprising an inorganic material.

[0023] In some embodiments, before forming the first capping layer on the side of the second electrode layer away from the substrate, the preparation method further includes: forming a second capping layer on the side of the second electrode layer away from the substrate, the second capping layer comprising an organic material.

[0024] The above-described display device and the method for manufacturing the display panel have the same structure and beneficial technical effects as the display panels provided in some of the above embodiments, and will not be described again here. Attached Figure Description

[0025] To more clearly illustrate the technical solutions in this disclosure, the accompanying drawings used in some embodiments of this disclosure will be briefly described below. Obviously, the drawings described below are only drawings of some embodiments of this disclosure, and those skilled in the art can obtain other drawings based on these drawings. In addition, the drawings described below can be regarded as schematic diagrams and are not intended to limit the actual size of the product, the actual flow of the method, the actual timing of the signals, etc. involved in the embodiments of this disclosure.

[0026] Figure 1 This is a structural diagram of a display device provided according to some embodiments;

[0027] Figure 2 for Figure 1 A cross-sectional view of the display device in the AA direction is provided.

[0028] Figure 3 This is a film layer structure diagram of a light-emitting device for a display panel according to some embodiments;

[0029] Figure 4 This is a diagram showing another film structure of a light-emitting device for a display panel according to some embodiments;

[0030] Figure 5This is another film layer structure diagram of a light-emitting device for a display panel according to some embodiments;

[0031] Figure 6 It shows Figure 4 and Figure 5 Voltage-current density curves and voltage-brightness curves of the display panel;

[0032] Figure 7 It shows Figure 4 and Figure 5 Brightness-current efficiency curves and brightness-maximum external quantum efficiency curves of the display panel;

[0033] Figure 8 The diagram shows the light emission angle distribution of the display panel excluding the cover layer;

[0034] Figure 9 A light emission angle distribution diagram of a display panel including an organic overlay but excluding an inorganic overlay is shown.

[0035] Figure 10 It shows Figure 4 The diagram shows the light emission angle distribution of the display panel.

[0036] Figure 11 It shows Figure 5 The diagram shows the light emission angle distribution of the display panel.

[0037] Figure 12 This is a flowchart of a method for manufacturing a display panel according to some embodiments. Detailed Implementation

[0038] The technical solutions in some embodiments of this disclosure will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this disclosure, and not all embodiments. All other embodiments obtained by those skilled in the art based on the embodiments provided in this disclosure are within the scope of protection of this disclosure.

[0039] Unless the context otherwise requires, throughout the specification and claims, the term "comprising" is interpreted as open-ended and encompassing, meaning "including, but not limited to." In the description of the specification, terms such as "one embodiment," "some embodiments," "exemplary embodiment," "example," or "some examples" are intended to indicate that a particular feature, structure, material, or characteristic associated with that embodiment or example is included in at least one embodiment or example of this disclosure. The illustrative representations of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics mentioned may be included in any suitable manner in any one or more embodiments or examples.

[0040] Hereinafter, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of embodiments of this disclosure, unless otherwise stated, "a plurality of" means two or more.

[0041] In describing some embodiments, the term "connection" and its derivative expressions may be used. The term "connection" should be interpreted broadly; for example, "connection" can be a fixed connection, a detachable connection, or an integral part; it can be a direct connection or an indirect connection through an intermediate medium.

[0042] "At least one of A, B and C" has the same meaning as "at least one of A, B or C", both including the following combinations of A, B and C: only A, only B, only C, combinations of A and B, combinations of A and C, combinations of B and C, and combinations of A, B and C.

[0043] "A and / or B" includes the following three combinations: A only, B only, and a combination of A and B.

[0044] The use of “applies to” or “configured to” in this article implies an open and inclusive language that does not preclude applicability to or configuration to devices that perform additional tasks or steps.

[0045] As used herein, “about,” “approximately,” or “approximately” includes the stated value and the average value within an acceptable range of deviation from the given value, wherein the acceptable range of deviation is determined by a person skilled in the art taking into account the measurement under discussion and the error associated with the measurement of the given quantity (i.e., the limitations of the measurement system).

[0046] As used herein, “parallel,” “perpendicular,” “orthogonal,” and “equal” include the described situation and situations that are similar to the described situation, within an acceptable range of deviation, which is determined by those skilled in the art taking into account the measurement under discussion and the error associated with the measurement of a particular quantity (i.e., the limitations of the measurement system). For example, “parallel” includes absolute parallelism and approximate parallelism, where an acceptable range of deviation for approximate parallelism may be, for example, within 5°; “perpendicular” includes absolute perpendicularity and approximate perpendicularity, where an acceptable range of deviation for approximate perpendicularity may also be, for example, within 5°; “equal” includes absolute equality and approximate equality, where an acceptable range of deviation for approximate equality may be, for example, a difference between the two equals being less than or equal to 5% of either one.

[0047] It should be understood that when a layer or element is referred to as being on another layer or substrate, it can mean that the layer or element is directly on the other layer or substrate, or that there is an intermediate layer between the layer or element and the other layer or substrate.

[0048] This document describes exemplary embodiments with reference to cross-sectional views and / or plan views, which are idealized exemplary drawings. In the drawings, the thickness of layers and the area of ​​regions are enlarged for clarity. Therefore, variations in shape relative to the drawings are contemplated due to, for example, manufacturing techniques and / or tolerances. Thus, exemplary embodiments should not be construed as being limited to the shapes of the regions shown herein, but rather include shape deviations due to, for example, manufacturing processes. For example, etched areas shown as rectangular would typically have curved features. Therefore, the regions shown in the drawings are schematic in nature, and their shapes are not intended to show the actual shapes of the areas of the device, nor are they intended to limit the scope of the exemplary embodiments.

[0049] Figure 1 This is a structural diagram of a display device according to some embodiments. Figure 1 As shown, embodiments of this disclosure provide a display device 1000, which is a product with image display functionality. Exemplarily, the display device 1000 can be any device that displays either moving (e.g., video) or fixed (e.g., still image) content, and whether it is text or an image.

[0050] For example, the display device 1000 can be any product or component with display functionality, such as a television, laptop, tablet, personal digital assistant (PDA), mobile phone, watch, clock, calculator, GPS receiver / navigator, camera, camera view display (e.g., a rearview camera display in a vehicle), wearable device, augmented reality (AR) device, virtual reality (VR) device, in-vehicle display, or flight display. Figure 1 As shown, the display device 1000 can be a mobile phone.

[0051] From the perspective of the light emission type of the display device 1000, the display device 1000 can be a quantum dot light emitting diode (QLED) display device. From the perspective of the shape of the display device 1000, the display device 1000 can be a flat display device, a curved display device, or a foldable display device, etc. From the perspective of the shape of the display device 1000, the display device 1000 can be rectangular or circular, etc. From the perspective of the light emission direction of the display device 1000, the display device 1000 can be a top-emitting display device or a bottom-emitting display device. The embodiments of this disclosure do not specifically limit this.

[0052] The following describes some embodiments of the present disclosure using the display device 1000 as an example of a top-emitting, rectangular, and planar quantum dot electroluminescent display device. However, the implementation of the present disclosure is not limited to this, and any other display device can be considered as long as the same technical concept is applied.

[0053] See Figure 1 In some embodiments, the display device 1000 includes a display area Q1 and a non-display area Q2 disposed adjacent to the display area Q1.

[0054] See Figure 2 , Figure 2 for Figure 1 A cross-sectional view of the display device along the AA direction is provided. Figure 2 As can be seen, the display device 1000 includes a display panel 1001 and a cover plate 1002. The cover plate 1002 is located on the light-emitting side of the display panel 1001 and is used to protect the display panel 1001. Optical adhesive (OCA) is also provided between the display panel 1001 and the cover plate 1002 for bonding the display panel 1001 and the cover plate 1002.

[0055] The display device 1000 also includes a circuit board 1003 connected to the display panel 1001. The circuit board 1003 is used, for example, to input various signals required for displaying images to the display panel 1001, such as control signals, power supply voltage signals, and data signals.

[0056] The display panel 1001 includes an array substrate 100, a light-emitting device layer 200, and a cover layer 300 stacked together.

[0057] The array substrate 100 includes a substrate 110 and a pixel circuit layer 120 stacked sequentially.

[0058] The substrate 110 is made of a transparent material. For example, the substrate 110 can be a transparent flexible substrate, or it can be a transparent rigid substrate, such as glass or ultrathin glass.

[0059] The pixel circuit layer 120 includes multiple pixel circuits configured to drive the light-emitting device layer 200 to emit light. The pixel circuit layer 120 may include multiple conductive layers, such as a semiconductor layer, a gate conductive layer, and a source / drain conductive layer sequentially disposed along a direction perpendicular to and away from the substrate 110. Of course, the array substrate may also include other conductive layers, such as one or more additional source / drain conductive layers, etc., without specific limitations here.

[0060] The aforementioned conductive layers form multiple thin film transistors (TFTs). The thin film transistors may include a semiconductor pattern located in the semiconductor layer, a gate located in the gate conductive layer, and a source and drain located in the source and drain conductive layers.

[0061] The pixel circuit layer 120 may also include an insulating layer located between adjacent conductive layers. For example, the array substrate 100 may include a gate insulating layer located between the semiconductor layer and the gate conductive layer, an interlayer dielectric layer located between the gate conductive layer and the source / drain conductive layer, and a planarization layer located between the source / drain conductive layer and the light-emitting device layer 200. Of course, the pixel circuit layer 120 may also include other insulating film layers, which will not be described in detail here.

[0062] The light-emitting device layer 200 includes a first electrode layer 201, a light-emitting functional layer 202, and a second electrode layer 203 stacked along a direction away from the array substrate 100. The light-emitting device layer 200 includes multiple light-emitting devices, one of which is connected to a pixel circuit, which drives the light-emitting device to emit light. The multiple light-emitting devices can include light-emitting devices of different colors, such as red, green, or blue, thereby enabling the display panel 1001 to display color images. Alternatively, the multiple light-emitting devices can all be white, all blue, or all red. In this case, a color conversion structure is provided above the light-emitting device layer 200 to convert a single color of light into the target color. The second electrode layers 203 of the multiple light-emitting devices are interconnected to form a continuous, integral layer structure.

[0063] In some embodiments, the first electrode layer 201 is configured as the cathode of the light-emitting device layer 200, and the second electrode layer 203 is configured as the anode of the light-emitting device layer 200; in other embodiments, the first electrode layer 201 is configured as the anode of the light-emitting device layer 200, and correspondingly, the second electrode layer 203 is configured as the cathode of the light-emitting device layer 200.

[0064] In some embodiments, the first electrode layer 201 is a semi-transparent and semi-reflective electrode, and the second electrode layer 203 is a reflective electrode. In this case, the display panel 1001 is a bottom-emitting display panel. In other embodiments, the first electrode layer 201 is a reflective electrode, and the second electrode layer 203 is a semi-transparent and semi-reflective electrode. In this case, the display panel 1001 is a top-emitting display panel. The embodiments disclosed herein do not specifically limit this type of display panel.

[0065] For example, the first electrode layer 201 may include indium tin oxide (ITO), and the first electrode layer 201 is selected, for example, from a reflective electrode composed of an ITO / metal / ITO stack structure. The second electrode layer 203 may be selected from a magnesium-silver electrode. During the fabrication process, the magnesium-silver material can suppress silver ion aggregation, improve the thickness uniformity of the second electrode layer 203, and thus improve the display effect of the display panel 1001. At the same time, the magnesium in the second electrode 203 has a low work function, which is beneficial for electron injection.

[0066] For example, see Figure 3 , Figure 3 This is a film layer structure diagram of a light-emitting device for a display panel according to some embodiments. The light-emitting functional layer 202 includes a light-emitting layer 230, and the light-emitting functional layer 202 may further include: at least one common layer, which includes any one or a combination of several of the following: a hole injection layer (HIL), a hole transport layer (HTL), an electron blocking layer (EBL), a hole blocking layer (HBL), an electron transport layer (ETL), and an electron injection layer (EIL).

[0067] exist Figure 3 In the process, the light-emitting functional layer 202 includes a light-emitting layer 230, which comprises quantum dot material. It should be understood that the light-emitting layer 230 may be selected from red, green, or blue light-emitting quantum dots, and this disclosure does not limit it.

[0068] The quantum dot material included in the light-emitting layer 230 can be semiconductor nanocrystals and can have various shapes. In some feasible embodiments, the quantum dots can be spherical, conical, multi-armed, and / or cubic nanoparticles, nanotubes, nanowires, nanofibers, nanoplate particles, quantum rods, or quantum sheets. Here, the quantum rods can be quantum dots with an aspect ratio (length-to-width ratio) greater than about 1, for example, greater than or equal to about 2, greater than or equal to about 3, or greater than or equal to about 5. For example, the quantum rods can have an aspect ratio less than or equal to about 50, less than or equal to about 30, or less than or equal to about 20.

[0069] In some feasible embodiments, quantum dots may have particle diameters of, for example, about 1 nm to about 100 nm, about 1 nm to about 80 nm, about 1 nm to about 50 nm, or about 1 nm to 20 nm (for non-spherical shapes, average maximum particle length).

[0070] In some feasible embodiments, the band gap of the quantum dot can be controlled according to its size and composition, thus controlling the emission wavelength of the quantum dot. For example, as the size of the quantum dot increases, it may have a narrow band gap and thus be configured to emit light in a relatively long wavelength region, while as the size of the quantum dot decreases, it may have a wide band gap and thus be configured to emit light in a relatively short wavelength region. For example, the quantum dot may be configured to emit light in a predetermined wavelength region of the visible light region, depending on its size and / or composition. For example, the quantum dot may be configured to emit blue light, red light, or green light, and the blue light may have a peak emission wavelength (λmax) in, for example, from about 430 nm to about 480 nm, the red light may have a peak emission wavelength (λmax) in, for example, from about 600 nm to about 650 nm, and the green light may have a peak emission wavelength (λmax) in, for example, from about 520 nm to about 560 nm.

[0071] In some feasible embodiments, the fabrication technology of the light-emitting layer 230 can be any one of inkjet printing, photolithography, or transfer printing. When photolithography is used to fabricate the light-emitting layer 230, the quantum dot light-emitting material can be patterned using direct photolithography. Specifically, the quantum dot light-emitting material is directly exposed and developed to change its solubility, thereby achieving patterning. Alternatively, a sacrificial layer can be used to pattern the quantum dot light-emitting material. Specifically, before forming the quantum dot light-emitting material, a sacrificial layer is formed in the area where the quantum dot light-emitting material needs to be removed, and the quantum dot light-emitting material is patterned using a sacrificial layer elution process.

[0072] In some feasible embodiments, the quantum dots may have a core-shell structure, with one quantum dot surrounding another. For example, the core and shell of the quantum dots may have an interface, and at least one element of the core or shell may have a concentration gradient at the interface, wherein the concentration of the element in the shell decreases toward the core. For example, the material composition of the shell of the quantum dot has a higher band gap than the material composition of the core of the quantum dot.

[0073] In some feasible embodiments, the quantum dot may have a quantum dot core and a multilayer quantum dot shell surrounding the core. Here, the multilayer shell has at least two shells, wherein each shell may be a single composition, an alloy, and / or have a concentration gradient. For example, the shells of the multilayer shell farther from the core may have a higher band gap than the shells closer to the core.

[0074] For example, such as Figure 3 As shown, the light-emitting functional layer 202 also includes a hole injection layer 210, a hole transport layer 220, and an electron transport layer 240. The hole injection layer 210, the hole transport layer 220, the light-emitting layer 230, and the electron transport layer 240 are stacked sequentially on the side of the first electrode layer 201 away from the array substrate 100.

[0075] The hole injection layer 210 is configured to reduce the hole injection resistance and improve the hole transport efficiency from the first electrode layer 201 to the light-emitting layer 230. For example, the hole injection layer 210 may include poly(3,4-ethylenedioxythiophene) (PEDOT) and polystyrene sulfonic acid (PSS).

[0076] Hole transport layer 220 is configured to transport holes from hole injection layer 210 to light-emitting layer 230. By selecting appropriate materials, hole loss during transport can be effectively reduced, thereby improving the display brightness of display panel 1001. For example, hole transport layer 220 may include poly((9,9-dioctylfluorenyl-2,7-diyl)-alt-(9-(2-ethylhexyl)-carbazole-3,6-diyl))(PF8Cz).

[0077] The electron transport layer 240 is configured to transport electrons from the light-emitting functional layer 202 to the light-emitting layer 230. Under normal circumstances, the electron transport layer 240 has high electronic conductivity, which improves the interface contact between the electron transport layer 240 and the hole transport layer 220, reduces the interface impedance between them, thereby reducing energy loss during charge transport. At the same time, it can also balance the distribution of electrons and holes, ensure effective pairing of electrons and holes in the light-emitting layer 230, and further improve the luminous efficiency and brightness of the display panel 1001. For example, the electron transport layer 240 may include at least one of nitrogen trifluoride (TPD), o-phenylenediamine (BPhen), tris(8-hydroxyquinoline)aluminum (Alq3), zinc oxide (ZnO), zinc magnesium oxide (ZnMgO), 1,3,5-tris(1-phenyl-1H-benzimidazol-2-yl)benzene (TPBi), 2,4,6-tris[3-(diphenylphosphinyl)phenyl]-1,3,5-triazine (PO-T2T), and tris[2,4,6-trimethyl-3-(pyridin-3-yl)phenyl]borane (3TPYMB). In this embodiment, the electron transport layer 240 includes, for example, zinc magnesium oxide.

[0078] In some feasible embodiments, the light-emitting functional layer 202 further includes an electron blocking layer located between the hole transport layer 220 and the light-emitting layer 230, configured to restrict electron movement to the hole transport layer 220 and / or the hole injection layer 210, thereby improving the light-emitting efficiency of the display panel 1001.

[0079] In some feasible embodiments, the light-emitting functional layer 202 further includes a hole-blocking layer located between the light-emitting layer 230 and the electron transport layer 240, configured to restrict hole movement to prevent holes from diffusing into the non-light-emitting area, thereby improving the luminous efficiency and brightness of the display panel 1001.

[0080] In some feasible embodiments, the light-emitting functional layer 202 further includes an electron injection layer located between the electron transport layer 240 and the second electrode layer 203, configured to improve the efficiency of electron transport from the second electrode layer 203 to the light-emitting layer 230 and reduce transport losses.

[0081] It should be understood that the light-emitting functional layer 202 may be a whole-surface structure or may be set independently of each other.

[0082] The capping layer 300 is located on the side of the light-emitting device layer 200 away from the array substrate 100. The capping layer 300 is configured to adjust the optical interference distance and suppress extinction caused by surface plasmon energy movement, thereby improving the light extraction rate and enhancing the display effect. It should be understood that the capping layer 300 can also reduce the adverse effects of external environmental factors such as water vapor and oxygen on the light-emitting functional layer 202, improve the stability of the light-emitting functional layer 202, and extend its service life.

[0083] When the cover layer 300 includes organic materials, although it can improve the luminous efficiency of the display panel 1001 to some extent while reducing the adverse effects of external environmental factors on the light-emitting functional layer 202, the organic materials used in the cover layer 300 may react with some materials used in the process of manufacturing the display panel 1001, reducing the display uniformity of the display panel 1001 and affecting its display effect.

[0084] For example, the non-display area Q2 includes a sealing adhesive 401 surrounding the display area Q1, and an encapsulation frame 402 surrounding the sealing adhesive 401. The sealing adhesive 401 is used, for example, to bond the encapsulation frame 402 to the display panel 1001. The encapsulation frame 402 cooperates with the cover plate 1002 to isolate the display panel 1001 from the external environment, preventing moisture, oxygen, and impurity ions from adversely affecting the display panel 1001. For example, the sealing adhesive 401 is selected from adhesives including acrylates, and the encapsulation frame 402 is selected from glass.

[0085] For example, see Figure 2 and Figure 3 The optical adhesive OCA used to bond the display panel 1001 and the cover plate 1002, and / or the sealing adhesive 401 used to bond the encapsulation frame 402 and the display panel 1001, react with the organic materials included in the second cover layer 302, changing the thickness of the second cover layer 302 and / or the optical adhesive in certain areas. This not only affects the thickness uniformity of both but also makes the interface between the optical adhesive OCA and the second cover layer 302 uneven. Furthermore, the reaction products of the optical adhesive OCA and / or the sealing adhesive 401 with the organic materials included in the second cover layer 302 also change the refractive index in that area, further affecting the display effect of the display panel 1001.

[0086] Figure 4 This is another film layer structure diagram of a light-emitting device for a display panel according to some embodiments. The display panel 1001 includes an array substrate 100, a first electrode layer 201, a light-emitting functional layer 202, a second electrode layer 203, and a first cover layer 301 stacked together.

[0087] The first cover layer 301 is disposed on the side of the second electrode layer 203 away from the array substrate 100. The first cover layer 301 is configured to adjust the optical interference distance, suppress external light reflection, and suppress extinction caused by surface plasma energy movement, thereby improving the light extraction rate and enhancing the display effect.

[0088] In some feasible embodiments, the first capping layer 301 is made of an inorganic material. For example, the material used for the first capping layer 301 is a metal oxide, such as at least one selected from molybdenum oxide, tungsten oxide, copper oxide, zinc oxide, aluminum oxide, or vanadium pentoxide.

[0089] Inorganic metal oxides are diverse and offer a wide range of choices, allowing for the selection of inorganic metal oxides that meet various requirements of the display panel 1001, such as manufacturing process, overall compatibility, refractive index, and light emission angle distribution, based on the specific application scenario. Furthermore, the inorganic material used to prepare the first cover layer 301 does not react with materials used in subsequent processes, such as optical adhesive OCA and / or sealing adhesive 401, which improves the display uniformity of the display panel 1001 and thus enhances its display performance.

[0090] In some feasible embodiments, the thickness of the first cover layer 301 is 15nm to 25nm. For example, the thickness of the first cover layer 301 can be 15nm, 18nm, 20nm, 22nm or 25nm.

[0091] In this embodiment, the first cover layer 301 is relatively thin, which is beneficial to the thinning of the display panel 1001, and this thickness is suitable for various colors of light-emitting quantum dots, including red light-emitting quantum dots, green light-emitting quantum dots and blue light-emitting quantum dots.

[0092] In some feasible embodiments, the refractive index of the first cover layer 301 is greater than or equal to 1.8; for example, the refractive index of the first cover layer 301 can be 2. Using a first cover layer 301 with a high refractive index can improve the light emission path, and the refractive index of the first cover layer 301 matches that of the second electrode layer 203, thereby improving the display effect of the display panel 1001.

[0093] In some feasible embodiments, the display panel 1001 further includes a second cover layer 302, such as Figure 5 As shown, Figure 5This is another film structure diagram of a light-emitting device for a display panel according to some embodiments. A second cover layer 302 is located between the second electrode layer 203 and the first cover layer 301. The second cover layer 302 also serves to adjust the optical interference distance, suppress external light reflection, and suppress extinction caused by surface plasmon energy movement, thereby improving the light extraction rate and enhancing the display effect of the display panel 1001. Simultaneously, the second cover layer 302 can also improve light coupling output and increase the light emission angle.

[0094] In some feasible embodiments, the second capping layer 302 is prepared using an organic material. For example, the material used for the second capping layer 302 may be N,N′-di(1-naphthyl)-N,N′-diphenyl-(1,1′-biphenyl)-4,4′-diamine (NPB), tris(4-carbazoyl-9-ylphenyl)amine (TCTA), or 1,1-bis[(di-4-methyl...] The second capping layer 302 may be made of at least one of aniline[(di-4-tolylamino)phenyl]cyclohexane (TAPC), 4,4′-bis(N-carbazolyl)-1,1′-biphenyl (CBP), or 1,3-bis(N-carbazolyl)benzene (mCP). It should be understood that the second capping layer 302 may also be made of other organic materials well known to those skilled in the art, and this disclosure does not limit it.

[0095] In some feasible embodiments, the thickness of the second cover layer 302 is 35nm to 45nm. For example, the thickness of the second cover layer 302 can be 35nm, 40nm or 45nm.

[0096] In some feasible embodiments, the refractive index of the second cover layer 302 is less than the refractive index of the first cover layer 301. For example, the refractive index of the second cover layer 302 is 1.85, and the refractive index of the first cover layer 301 is 2. The refractive index of the first cover layer 301 is greater than that of the second cover layer 302, which can effectively increase the light emission of the display panel 1001, thereby improving the display effect of the display panel 1001.

[0097] By reasonably setting the refractive index of the first cover layer 301 and the second cover layer 302, the light output angle distribution and current efficiency of the display panel 1001 can be significantly improved, thereby improving the display effect of the display panel 1001.

[0098] refer to Figure 6 , Figure 6 It shows Figure 4 and Figure 5 The voltage-current density curve and voltage-brightness curve of the display panel are shown. For easy comparison, Figure 6 The image also shows voltage-current density curves and voltage-brightness curves for a display panel 1001 excluding the cover layer 300 and a display panel 1001 including the second cover layer 302 but excluding the first cover layer 301. Figure 6 In the graph, the horizontal axis represents voltage in volts; the solid line represents the voltage-current density curve, corresponding to the current density on the left vertical axis, in milliamperes per square centimeter; and the dashed line represents the voltage-brightness curve, corresponding to the brightness on the right vertical axis, in candela per square centimeter.

[0099] First, let's explain the voltage-current density curves of the solid line portion. The first curve represents the voltage-current density of the display panel 1001 excluding the cover layer 300; the second curve represents the voltage-current density of the display panel 1001 including the second cover layer 302 but excluding the first cover layer 301; and the third curve represents the voltage-current density of the display panel 1001 including both the first and second cover layers 301. Figure 5 The voltage-current density curves of the display panel 1001 shown are shown. The fourth curve includes the first cover layer 301 but does not include the second cover layer 302. Figure 4 The voltage-current density curve of the display panel 1001 is shown below. Figure 6 As can be seen, when the voltage is less than or equal to 2V, the first to fourth curves almost overlap and are all 0. When the voltage is greater than 2V, as the voltage increases, the first to fourth curves also increase, and the trends of change of the first to fourth curves are similar. Overall, at the same voltage, the current density corresponding to the second curve > the current density corresponding to the third curve > the current density corresponding to the fourth curve > the current density corresponding to the first curve. It can be seen that adding the cover layer 300 can increase the current density of the display panel 1001. From a local perspective, for example, when the voltage is 4V, the current density of the display panel 1001 is increased by the current density of the second curve > the current density corresponding to the third curve > the current density corresponding to the fourth curve > the current density corresponding to the first curve. Figure 6 As can be seen, the brightness corresponding to the second to fourth curves is much greater than that corresponding to the first curve, which means that the 300-layer cover layer has a significant effect on improving the current density.

[0100] At the same voltage, increasing the current density can not only improve the brightness and enhance the display effect of the display panel 1001, but also make the display panel 1001 suitable for high light environments. It can also improve energy efficiency, reduce the power consumption and heat generation of the display panel 1001, reduce the heat loss of the display panel 1001, and improve its overall performance, stability and service life.

[0101] Next, the voltage-brightness curves of the dashed lines will be explained. The fifth curve represents the voltage-brightness curve of the display panel 1001 excluding the cover layer 300; the sixth curve represents the voltage-brightness curve of the display panel 1001 including the second cover layer 302 but excluding the first cover layer 301; and the seventh curve represents the voltage-brightness curve including both the first and second cover layers 301. Figure 5 The voltage-brightness curve of the display panel 1001 shown is shown in the eighth curve, which includes the first cover layer 301 but does not include the second cover layer 302. Figure 4 The voltage-brightness curve of the display panel 1001 shown is presented. Figure 6 As can be seen, when the voltage is less than 2V, the brightness corresponding to curves 5 through 8 is irregularly distributed between 1 and 10 candela. When the voltage is greater than 2V, the brightness corresponding to curves 5 through 8 increases with increasing voltage, and the trend of change of curves 5 through 8 is similar. Overall, under the same voltage, the brightness corresponding to curve 2 > the brightness corresponding to curve 3 > the brightness corresponding to curve 4 > the brightness corresponding to curve 1. It should be noted that when the voltage is greater than 3V, the brightness corresponding to curve 4 is close to that corresponding to curve 3. It can be seen that the cover layer 300 can improve the brightness of display panel 1001. From a local perspective, for example, when the voltage is 4V, the brightness of the display panel 1001 is significantly improved. Figure 6 As can be seen, the brightness corresponding to curves 6 through 8 is much greater than that corresponding to curve 4, which means that the 300 overlay layer has a significant effect on improving brightness.

[0102] At the same voltage, increasing the brightness of the display panel 1001 can not only improve energy efficiency and reduce power consumption, but also improve the contrast, color stability and consistency of the display panel 1001, and effectively improve the dynamic display effect of the display panel 1001.

[0103] Depend on Figure 6 It can be seen that, compared to display panel 1001 excluding cover layer 300, Figure 4 The display panel 1001 shown and Figure 5 The display panel 1001 shown has high current density and high brightness, and has the advantages of good display effect, low power consumption and long service life.

[0104] refer to Figure 7 , Figure 7 It shows Figure 4 and Figure 5 The brightness-current efficiency curves and brightness-maximum external quantum efficiency curves of the display panel are shown. For ease of comparison, Figure 7The image also shows luminance-current efficiency curves and luminance-maximum external quantum efficiency (EQE) curves for a display panel 1001 excluding the cover layer 300 and a panel including the second cover layer 302 but excluding the first cover layer 301. Figure 7 In the graph, the horizontal axis represents brightness in candela per square meter; the solid line represents the brightness-current efficiency curve, corresponding to the left vertical axis in candela per ampere; and the dashed line represents the brightness-maximum external quantum efficiency curve, corresponding to the right vertical axis.

[0105] First, let's explain the brightness-current efficiency curves of the solid line portion. The first curve represents the brightness-current efficiency of the display panel 1001 excluding the cover layer 300; the second curve represents the brightness-current efficiency of the display panel 1001 including the second cover layer 302 but excluding the first cover layer 301, where the thickness of the second cover layer 302 can be 60nm; the third curve represents the brightness-current efficiency of the display panel 1001 including both the first and second cover layers 301. Figure 5 The brightness-current efficiency curve of the display panel 1001 is shown. Here, the thickness of the first cover layer 301 can be 20nm, and the thickness of the second cover layer 302 can be 40nm; the fourth curve includes the first cover layer 301 but does not include the second cover layer 302, i.e. Figure 4 The brightness-current efficiency curve of the display panel 1001 shown is illustrated here, where the thickness of the first cover layer 301 can be 20nm. Figure 7 As can be seen overall, the current efficiencies of the second and fourth curves are greater than those of the first and third curves, and the first to fourth curves show a trend of first increasing and then decreasing. Locally, when the brightness is less than 2000 candela per square meter, the current efficiency of the first curve is greater than that of the third curve, and the current efficiency of the fourth curve is greater than that of the second curve; when the brightness is between 2000 and 7000 candela per square meter, the current efficiency of the third curve is greater than that of the first curve, and the current efficiency of the fourth curve is greater than that of the second curve; when the brightness is greater than 7000 candela per square meter, the current efficiency of the third curve is greater than that of the first curve, and the current efficiency of the second curve is greater than that of the fourth curve.

[0106] Figure 7 The brightness on the horizontal axis covers the vast majority of usage scenarios. As can be seen, the fourth curve exhibits high current efficiency across all brightness levels, consistently exceeding 75% and remaining relatively stable. This indicates... Figure 4The display panel 1001 shown, including the first cover layer 301 but excluding the second cover layer 302, has high and stable current efficiency, which helps to improve the display effect and lifespan of the display panel 1001. Meanwhile, the fourth curve and the first curve have the most similar overall trend and shape, that is... Figure 4 The display uniformity and display effect of the display panel 1001 shown are closest to those of the display panel 1001 without the overlay 300, which indicates that Figure 4 The display panel 1001 shown has the advantages of both high current efficiency and good display uniformity.

[0107] The following explains the brightness-maximum external quantum efficiency curves for the dashed lines. The fifth curve represents the brightness-maximum external quantum efficiency of the display panel 1001 excluding the cover layer 300; the sixth curve represents the brightness-maximum external quantum efficiency of the display panel 1001 including the second cover layer 302 but excluding the first cover layer 301; and the seventh curve represents the brightness-maximum external quantum efficiency of the display panel 1001 including both the first and second cover layers 301. Figure 5 The brightness-maximum external quantum efficiency curve of the display panel 1001 shown is shown in the eighth curve, which includes the first cover layer 301 but excludes the second cover layer 302. Figure 4 The brightness-maximum external quantum efficiency curves of the display panel 1001 are shown below. Specifically, when the brightness is less than 200 candela per square meter, the maximum external quantum efficiency of the eighth curve > the sixth curve > the fifth curve > the seventh curve; when the brightness is between 200 and 300 candela per square meter, the maximum external quantum efficiency of the sixth curve > the eighth curve > the fifth curve > the seventh curve; when the brightness is between 300 and 5000 candela per square meter, the maximum external quantum efficiency of the sixth curve > the eighth curve > the seventh curve > the fifth curve; and when the brightness is greater than 5000 candela per square meter, the maximum external quantum efficiency of the sixth curve > the seventh curve > the eighth curve > the fifth curve.

[0108] As can be seen, the eighth curve exhibits a high maximum external quantum efficiency at various brightness levels, ranging from 17.15% to 23.2%, with a small difference between the extreme values, indicating overall stability. Furthermore, the eighth curve and the fifth curve show the most similar overall trends and shapes. Figure 4 The display uniformity and display effect of the shown display panel 1001 are closest to those of the display panel 1001 without the overlay 300, further explained. Figure 4 The display panel 1001 shown has the advantages of high maximum external quantum efficiency and good display uniformity.

[0109] Next, see Figures 8 to 11 , Figure 8 The diagram shows the light emission angle distribution of the display panel excluding the cover layer. Figure 9 A light emission angle distribution diagram of a display panel including an organic overlay but excluding an inorganic overlay is shown. Figure 10 It shows Figure 4 The diagram shown illustrates the light emission angle distribution of the display panel. Figure 11 It shows Figure 5 The diagram shows the light emission angle distribution of the display panel. The solid lines represent the measured light emission angle distribution of the display panel, and the dashed lines represent the Lambert distribution of the light emission angle. Figures 8 to 11 As can be seen, after normalization, the display panels all exhibit a top-enhanced state, and the distribution shape of the light emission angle is basically elliptical.

[0110] Specifically, in comparison Figure 8 and Figure 10 As you can see, Figure 4 The light emission angle distribution diagram of the display panel 1001 shown is basically consistent with the light emission angle distribution diagram of the display panel 1001 excluding the cover layer 300, indicating that... Figure 4 The display panel 1001 that uses metal oxide as the first cover layer 301 has an overall display uniformity that is closest to that of a display panel 1001 without a cover layer 300. Figure 6 and Figure 7 It can be seen that, Figure 4 The display panel 1001 shown significantly improves the brightness, current density, current efficiency, and maximum external quantum efficiency of the display panel 1001 without adversely affecting the angular distribution of the display panel 1001, thereby bringing better display uniformity and display effect.

[0111] contrast Figure 8 and Figure 11 As you can see, Figure 5 The light emission angle distribution of the display panel 1001 shown is better than that of the display panel 1001 excluding the cover layer 300, combined with Figure 6 and Figure 7 It can be seen that, Figure 5 The display panel 1001 shown improves the brightness, current density, current efficiency, and maximum external quantum efficiency of the display panel 1001, while also improving the light emission angle distribution of the display panel 1001, thereby enhancing the viewing angle and display effect of the display panel 1001. Furthermore, due to... Figure 5The display panel 1001 shown also includes a first cover layer 301 made of metal oxide, which isolates the second cover layer 302 from the optical adhesive OCA, preventing the optical adhesive OCA from reacting with the organic materials included in the second cover layer 302, thereby improving the display uniformity of the display panel 1001 to a certain extent.

[0112] contrast Figure 8 and Figure 9 and combined Figure 6 and Figure 7 As can be seen, although the display panel 1001, which includes the second cover layer 302 but not the first cover layer 301, has a better light emission angle distribution, its brightness, current density, current efficiency, and maximum external quantum efficiency are all reduced, and its stability is poor. Figure 7 The efficiency of the medium current varies significantly under low and high brightness, resulting in excessive changes in the display effect of the display panel 1001 when the brightness changes. In addition, the second cover layer 302, which is made of organic material, is easily damaged by subsequent processes and external environmental factors, resulting in poor display effect, poor light emission morphology and short service life of the display panel 1001.

[0113] Figure 12 The flowchart of a method for manufacturing a display panel according to some embodiments includes steps S10 to S30.

[0114] The following combination Figure 2 , Figure 4 and Figure 12 This disclosure describes a method for fabricating a display panel according to some embodiments. In step S10, a first electrode layer 201, a light-emitting functional layer 202, and a second electrode layer 203 are sequentially stacked on a substrate 110. The substrate 110 can be a transparent flexible substrate, or it can be a transparent rigid substrate, such as glass or ultrathin glass. The first electrode layer 201 can be a reflective anode composed of an ITO / metal / ITO stack; the light-emitting functional layer 202 includes a light-emitting layer 230, which, exemplarily, is selected from a quantum dot light-emitting layer. It should be understood that the light-emitting layer 230 can be selected from red, green, or blue light-emitting quantum dots; the second electrode layer 203 can be a cathode composed of magnesium-silver electrodes.

[0115] In some feasible embodiments, the light-emitting functional layer 202 further includes at least one of a hole injection layer 210, a hole transport layer 220, and / or an electron transport layer 240.

[0116] In some feasible embodiments, the light-emitting functional layer 202 further includes at least one of a hole injection layer, a hole transport layer, an electron blocking layer, an electron transport layer, and / or an electron injection layer.

[0117] In some feasible embodiments, before step S10, the method further includes: forming a pixel circuit layer 120 on the substrate 110, the pixel circuit layer 120 including a plurality of pixel circuits to drive a light-emitting device to emit light, the light-emitting device including a first electrode layer 201, a light-emitting functional layer 202 and a second electrode layer 203 formed in step S10.

[0118] For example, the pixel circuit layer 120 includes a plurality of conductive layers and an insulating layer located between adjacent conductive layers.

[0119] In step S30, a first capping layer 301 is formed on the side of the second electrode layer 203 away from the substrate 110. The first capping layer 301 comprises an inorganic material. The inorganic material is selected from metal oxides. For example, the inorganic material may be selected from at least one of molybdenum oxide, tungsten oxide, copper oxide, zinc oxide, aluminum oxide, or vanadium pentoxide.

[0120] In some feasible embodiments, the thickness of the first cover layer 301 can be from 15nm to 25nm. For example, the thickness of the first cover layer 301 can be 15nm, 18nm, 20nm, 22nm or 25nm.

[0121] In some feasible embodiments, the refractive index of the first cover layer 301 is greater than or equal to 1.8; for example, the refractive index of the first cover layer 301 may be 2.

[0122] In some feasible embodiments, the method for preparing the display panel further includes step S20, which is located before step S30.

[0123] The following combination Figure 2 , Figure 5 and Figure 12 The method for manufacturing the display panel of this embodiment will be described.

[0124] In step S20, a second capping layer 302 is formed on the side of the second electrode layer 203 away from the substrate 110. The second capping layer 302 comprises an organic material. The organic material used to prepare the second capping layer 302 can be selected from aromatic amine derivatives. It should be understood that the second capping layer 302 can also be made of other organic materials well known to those skilled in the art, and this disclosure does not limit it.

[0125] In some feasible embodiments, the thickness of the second cover layer 302 is 35nm to 45nm. For example, the thickness of the second cover layer 302 can be 35nm, 40nm or 45nm.

[0126] In some feasible embodiments, the refractive index of the second cover layer 302 is less than the refractive index of the first cover layer 301. For example, the refractive index of the first cover layer 301 is 2 and the refractive index of the second cover layer 302 is 1.85.

[0127] When the method for manufacturing a display panel includes step S20, the phrase “forming a first cover layer 301 on the side of the second electrode layer 203 away from the substrate 110” in step S30 can be interpreted as forming the first cover layer 301 on the side of the second cover layer 302 away from the substrate 110, that is, the second cover layer 302 is located between the second electrode layer 203 and the first cover layer 301.

[0128] In the display panel prepared by the method disclosed herein, an inorganic material is used as the first cover layer. This material does not react with materials used in subsequent processes, such as optical adhesives and / or sealing adhesives, thereby improving the display uniformity and thus enhancing the display effect. The use of an inorganic first cover layer significantly improves the current density, brightness, current efficiency, and maximum external quantum efficiency of the display panel without adversely affecting its light emission angle distribution. This enhances display uniformity, reduces power consumption, improves stability and lifespan, resulting in a better display performance.

[0129] In some embodiments, the display panel further includes a second cover layer. By reasonably setting the refractive indices of the first cover layer and the second cover layer, the light output angle distribution and current efficiency of the display panel can be significantly improved, thereby improving the display effect of the display panel.

[0130] The above description is merely a specific embodiment of this disclosure, but the scope of protection of this disclosure is not limited thereto. Any variations or substitutions conceived by those skilled in the art within the scope of the technology disclosed in this disclosure should be included within the scope of protection of this disclosure. Therefore, the scope of protection of this disclosure should be determined by the scope of the claims.

Claims

1. A display panel, characterized by, Comprising: a substrate; a first electrode layer, a light-emitting functional layer, and a second electrode layer, which are sequentially stacked on one side of the substrate away from the substrate; the light-emitting functional layer comprises a light-emitting layer, and the light-emitting layer comprises quantum dot material; and a first cover layer on the side of the second electrode layer away from the substrate, the first cover layer comprising inorganic material.

2. The display panel of claim 1, wherein, The inorganic material is selected from metal oxides.

3. The display panel of claim 2, wherein, The metal oxide is selected from at least one of molybdenum oxide, tungsten oxide, copper oxide, zinc oxide, aluminum oxide, or vanadium pentoxide.

4. The display panel of claim 1, wherein, The thickness of the first cover layer is 15-25 nm.

5. The display panel of claim 1, wherein, The refractive index of the first cover layer is greater than or equal to 1.

8.

6. The display panel of any one of claims 1-5, wherein, Further comprising: a second cover layer between the second electrode layer and the first cover layer, the second cover layer comprising organic material.

7. The display panel of claim 6, wherein, The refractive index of the second cover layer is less than that of the first cover layer.

8. The display panel of claim 7, wherein, The refractive index of the first cover layer is 2, and the refractive index of the second cover layer is 1.

85.

9. The display panel of claim 6, wherein, The thickness of the second cover layer is 35-45 nm.

10. The display panel of claim 6, wherein, The material of the second cover layer is selected from at least one of N,N'-di(1-naphthyl)-N,N'-diphenyl-(1,1'-biphenyl)-4,4'-diamine, tris(4-carbazoyl-9-ylphenyl)amine, 1,1-bis[(di-4-toluidinyl)phenyl]cyclohexane, 4,4'-bis(N-carbazolyl)-1,1'-biphenyl, and 1,3-bis(N-carbazolyl)benzene.

11. The display panel of any one of claims 1-10, wherein, The maximum external quantum efficiency of the display panel is 17-30%.

12. A display device, characterized by comprising: Comprising: a circuit board, and the display panel of any one of claims 1-11, connected to the circuit board.

13. The display device according to claim 12, characterized by Further comprising: an encapsulation frame disposed around the display panel; an encapsulation adhesive between the encapsulation frame and the display panel, configured to bond the encapsulation frame and the display panel.

14. A method for manufacturing a display panel, characterized by, Comprising: sequentially stacking a first electrode layer, a light-emitting functional layer, and a second electrode layer on a substrate; forming a first cover layer on the side of the second electrode layer away from the substrate, the first cover layer comprising inorganic material.

15. The method of claim 14, wherein, Before forming the first cover layer on the side of the second electrode layer away from the substrate, further comprising: forming a second cover layer on the side of the second electrode layer away from the substrate, the second cover layer comprising organic material.

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