CN114203930B - Cathode, organic light-emitting diode and preparation method thereof - Google Patents
Cathode, organic light-emitting diode and preparation method thereof Download PDFInfo
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- CN114203930B CN114203930B CN202111497345.9A CN202111497345A CN114203930B CN 114203930 B CN114203930 B CN 114203930B CN 202111497345 A CN202111497345 A CN 202111497345A CN 114203930 B CN114203930 B CN 114203930B
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Abstract
Some embodiments of the present application disclose a cathode, an organic light emitting diode, and a method of manufacturing the same. The cathode is a graphene cathode. The graphene has higher light transmittance, better foldability, water and oxygen corrosion resistance and higher conductivity, and after being used as a laminated graphene cathode, the light emitting effect, the bending resistance and the conductivity of the organic light emitting diode in each embodiment of the application are all superior to those of the organic light emitting diode which only adopts a pure metal cathode or a metal alloy cathode in the prior art, so that the cathode of each embodiment of the application is particularly suitable for the organic top light emitting diode.
Description
Technical Field
The application relates to the technical field of display, in particular to a cathode, an organic light-emitting diode and a preparation method thereof.
Background
The cathodes of OLED display devices (Organic light emitting diodes) are currently mostly made of metallic materials, such as Ag, al or Mg/Ag alloys. These metal materials themselves have poor light transmittance, and further decrease in light transmittance due to oxidation after a lapse of time, so that it is difficult to satisfy the requirement of light emission from the cathode, thereby affecting the display effect of the manufactured top emission (Topemission) device. In addition, the metal material itself is also easily oxidized to generate a metal oxide, which results in poor stability of the metal electrode, thereby affecting the display effect thereof. Furthermore, the cathode of the top light emitting device tends to be thin in order to ensure light transmittance, which results in poor conductivity thereof, limiting the number of electrons injected into the light emitting layer, and thus further limiting the display effect of the light emitting layer. In addition, if the metal electrode is used for a flexible display device, since the flexible display device needs to have good bending performance of each layer, and the hardness of the metal cathode is large, the bending type is poor, and bending marks can be left when the metal electrode is bent for many times, so that the visual effect of the flexible display device can be influenced, and the actual display effect of the flexible display device can be also influenced.
Disclosure of Invention
It is an object of some embodiments of the present application to provide a cathode, an organic light emitting diode and a method of manufacturing the same. Some embodiments of the present disclosure can solve the problem of poor light emission from a cathode due to oxidation of a metal cathode of an existing top-emission display screen. Other embodiments of the present application can solve the problem of poor conductive performance caused by too thin metal cathodes of the existing top emission type. Other embodiments of the present application can solve the problem that a metal cathode of a flexible display screen is prone to remain creased due to being folded multiple times. Still other embodiments of the present application can also solve the above-mentioned technical problems simultaneously, thereby being beneficial to improving the display effect of the top-emission flexible display screen or the top-emission rigid display screen as a whole.
Some embodiments of the present application provide a cathode for an organic light emitting diode, where the cathode is a graphene laminate formed by stacking a plurality of graphene sheets, the thickness of each graphene sheet ranges from 0.332nm to 0.357nm, the number of layers formed by stacking graphene sheets is any integer from 35 layers to 55 layers, and the work function of the cathode is any integer from 2.5eV to 3 eV.
In some embodiments of the present application, the thickness of the cathode may be selected from any one of values from 15nm to 20 nm.
Some embodiments of the present application provide a method for preparing a cathode for an organic light emitting diode, comprising the steps of:
(1) Preparing a graphene material by adopting a redox method;
(2) And depositing a graphene material to obtain a graphene laminated layer formed by stacking a plurality of graphene sheets, wherein the graphene laminated layer is used as a cathode of the organic light-emitting diode.
In some embodiments of the present application, the thickness of each graphene sheet layer may range from any one value of 0.332nm to 0.357nm, the number of layers formed by stacking the graphene sheet layers may be any one integer of 35 layers to 55 layers, and the work function of the cathode may be any one value of 2.5eV to 3 eV.
In some embodiments of the present application, the preparation method of the graphene material is a redox method, and the preparation method thereof includes the following steps: and (3) reacting natural graphite with an oxidant to generate graphite oxide, preparing single-layer graphite oxide after ultrasonic dispersion, and adding a reducing agent to remove oxygen-containing groups on the surface of the single-layer graphite oxide to obtain the graphene material.
In some embodiments of the present application, the oxidizing agent includes a strong oxidizing substance and a strong acid. The strongly oxidizing substance includes: potassium permanganate, hydrogen peroxide or KClO 4 . The strong acid includes: concentrated sulfuric acid or fuming HNO 3 。
In some embodiments of the present application, the reducing agent comprises: dimethylhydrazine, hydrazine hydrate, sodium borohydride or hydroiodic acid. The oxygen-containing group includes carboxyl, epoxy, hydroxyl, and the like.
In some embodiments of the present application, the thickness of the cathode may be selected from any one of values from 15nm to 20 nm.
Some embodiments of the present application also provide an organic light emitting diode, including: the device comprises a substrate, an anode layer, a hole injection layer, a hole transport layer, a light emitting layer, an electron transport layer, a cathode layer and a sealing layer which are sequentially arranged from bottom to top. After the structure is encapsulated, an encapsulation layer is also formed.
The cathode layer is a graphene lamination formed by stacking a plurality of graphene sheets, the thickness of each graphene sheet ranges from 0.332nm to 0.357nm, the number of layers formed by stacking the graphene sheets is any integer from 35 layers to 55 layers, and the work function of the cathode is any value from 2.5eV to 3 eV.
In some embodiments of the present application, the thickness of the anode layer is any one of a number in the range of 25nm to 55 nm.
In some embodiments of the present application, the hole injection layer has a thickness in the range of any one of 20nm to 40nm.
In some embodiments of the present application, the thickness of the hole transport layer ranges from any one of 15nm to 35 nm.
In some embodiments of the present application, the thickness of the light emitting layer is any one value in the range of 12nm to 45 nm.
In some embodiments of the present application, the electron transport layer has a thickness in the range of any one of 3nm to 15 nm.
In some embodiments of the present application, the thickness of the cathode layer is selected from any one of values from 15nm to 20 nm.
Some embodiments of the present application also provide a method for preparing an organic light emitting diode, which includes the following steps:
(1) Sequentially forming a substrate, an anode layer, a hole injection layer, a hole transport layer, a light emitting layer and an electron transport layer from bottom to top;
(2) Depositing graphene materials on the upper surface of the electron transport layer by layer in inert atmosphere, forming a graphene sheet layer every time one graphene sheet layer is deposited, and sequentially depositing a plurality of graphene sheets to obtain a cathode layer formed by stacking the graphene sheets;
(3) And forming a sealing layer on the cathode layer, and packaging to obtain the organic light-emitting diode.
Wherein, the thickness range of each graphene sheet layer is any one value in 0.332nm to 0.357nm, the number of layers formed by stacking the graphene sheet layers is any one integer in 35 layers to 55 layers, and the work function of the cathode layer is any one value in 2.5eV to 3 eV.
In some embodiments of the present application, the thickness of the cathode may be selected from any one of values from 15nm to 20 nm.
By adopting the technical scheme of the embodiments or any combination thereof, some embodiments of the present application achieve the following beneficial effects:
in some embodiments of the present application, the cathode of the organic light emitting diode is a graphene cathode. The graphene has higher light transmittance, better foldability, water and oxygen corrosion resistance and higher conductivity, and after the graphene lamination is used as the cathode, the light emitting effect, the bending resistance and the conductivity of the organic light emitting diode in the embodiment of the application are all superior to those of the organic light emitting diode which only adopts a pure metal cathode or a metal alloy cathode in the prior art, so that the cathode of each embodiment of the application is particularly suitable for the organic top light emitting diode.
Drawings
In order to more clearly illustrate the technical solutions of the embodiments of the present application, the drawings that are needed in the description of the embodiments will be briefly introduced below, it being obvious that the drawings in the following description are only some embodiments of the present application, and that other drawings may be obtained according to these drawings without inventive effort for a person skilled in the art.
Fig. 1 is a schematic structural diagram of an organic top-emitting diode in some embodiments of the present application. Arrows indicate light direction.
Detailed Description
The following description of the embodiments of the present application will be made clearly and completely with reference to the drawings (if any) of the embodiments of the present application, and it is apparent that the described embodiments are only some embodiments of the present application, but not all embodiments. All other embodiments, which can be made by those skilled in the art based on the embodiments herein without making any inventive effort, are intended to be within the scope of the present application. Furthermore, it should be understood that the detailed description is presented herein for purposes of illustration and explanation only and is not intended to limit the present application. In this application, unless otherwise indicated, terms of orientation such as "upper" and "lower," if any, are generally used herein to refer to the upper and lower aspects of the device in its actual or operational state, and specifically to the orientation of the drawing figures; while "inner" and "outer" (if any) are for the contour of the device.
Reference in the specification to "an embodiment" means that a particular feature, structure, or characteristic described in connection with the embodiment may be included in at least one embodiment of the application. The appearances of such phrases in various places in the specification are not necessarily all referring to the same embodiment, nor are separate or alternative embodiments mutually exclusive of other embodiments. Those of skill in the art will explicitly and implicitly appreciate that the embodiments described herein can be arbitrarily combined or combined with other embodiments to form new embodiments.
The terms "first," "second," "third," and "fourth," etc., in this application, if any, are used for distinguishing between different objects and not for describing a particular sequential order. Furthermore, the terms "comprise" and "have," if any, and any variations thereof, are intended to cover a non-exclusive inclusion. For example, a process, method, system, article, or apparatus that comprises a list of steps or modules is not limited to only those steps or modules but may include other steps or modules not expressly listed or inherent to such process, method, article, or apparatus.
Some embodiments of the present application provide a cathode for an organic top-emitting diode. The organic top light emitting diode in these embodiments may include both flexible organic top light emitting diodes and rigid organic top light emitting diodes. The light emission mode of the organic top light emitting diode is a top emission mode (topemition). In the top emission mode, light emitted from the light emitting layer is emitted from the cathode, which requires the cathode to have a certain light transmittance, otherwise, poor display effect is caused. In addition, on the premise of ensuring that the cathode has certain light transmittance, the thickness of the cathode is not required to be too thin, otherwise, the electron transmission of the cathode is influenced, so that the electron transmission number of the cathode to the light-emitting layer is influenced, and the display effect is further influenced. Furthermore, if the cathode is applied to a flexible organic top light emitting diode, the cathode needs to have good bending resistance (or flexibility), no obvious bending trace (or crease) is left after the cathode is subjected to more than ten thousands of times of folding, otherwise, the existence of the crease can affect the light emitting effect of the cathode, and further the display effect of the whole flexible display screen is affected. In addition, the cathode in the above embodiment is required to have a certain oxidation resistance, one of which may be: the packaging layer is possibly damaged when the flexible display screen is bent for a plurality of times, so that the cathode is easily affected by water and oxygen to be oxidized, oxidized spots are formed on the surface of the cathode after the cathode is oxidized, the light transmittance of the oxidized spots is different from that of the non-oxidized areas, the light transmittance of the light emergent surface of the whole cathode is uneven, the light emergent effect of the cathode is affected, and the display effect of the whole flexible display screen is affected.
The cathode of some embodiments of the present application can solve the above technical problems separately or simultaneously. The cathodes of these embodiments either have a certain oxidation resistance, or have reliable bending properties, or have good electrical conductivity, or have better light transmittance, or have all the advantages described above. The cathode in various embodiments of the present application can function as the cathode of either a flexible organic top light emitting diode, a rigid organic top light emitting diode, a flexible organic bottom light emitting diode (i.e., light emerging from the anode), or a rigid organic bottom light emitting diode. The following embodiments are described with reference to the cathode of the organic top light emitting diode, but the application of the cathode is not limited to the organic top light emitting diode. The following embodiments may be combined arbitrarily, and new embodiments may be formed without inventive effort.
Some embodiments of the present application provide a cathode that is a graphene stack of multiple graphene sheets stacked.
In some embodiments of the present application, the thickness of each graphene sheet layer may range from any one of 0.332nm to 0.357nm, may also range from 0.335nm, and so on.
In some embodiments of the present application, the number of layers of graphene sheets stacked may be any integer from 35 layers to 55 layers. In other embodiments of the present application, the number of graphene sheets may be 37, 38, 40, 41, 42, 43, 45, 47, 48, 49, 51, 52, 53, etc.
In some embodiments of the present application, on the premise that two adjacent graphene layers have a certain interlayer distance, the number of graphene layers in the graphene laminate cannot be too large, otherwise the light transmittance is affected, so in some embodiments, if 35 to 55 graphene materials are contained in the graphene layers, the overall thickness of the graphene laminate can be in the range of 15nm to 20nm, so that the light transmittance is not significantly affected. In order to enable the cathode to have better light transmittance, the overall film thickness of the cathode needs to be smaller than 15nm, and the cathode in the embodiment of the application is made of Graphene materials (Graphene), so that the limitation of the thickness can be overcome, the final thickness can be larger than 15nm, and the cathode can be suitable for display screens with smaller sizes or larger sizes and other specific sizes, and therefore the cathode has wider application range in the aspects of size and the like than the existing cathode materials. Meanwhile, since the thickness of the cathode in the embodiment of the application is larger than 15nm, the conductivity is better than that of the metal electrode, and the efficiency of carrier recombination is improved. On the other hand, the thickness of the graphene cannot be too thick, otherwise the transmittance of light is affected. In order to match the thickness of the cathode, the work function of the cathode needs to be adjusted to any one of 2.5eV to 3 eV.
In some embodiments of the present application, the graphene sheets have a thickness ranging from 0.332 to 0.357nm, and may be, for example, 0.335nm, and the like. The graphene sheets are made of graphene material. The carbon atoms in the graphene material are arranged in a honeycomb shape to form a carbon atom two-dimensional structure with a monoatomic layer, so that the graphene has excellent conductivity, stable chemical property, high light transmittance to visible light and good mechanical property, and is suitable for preparing OLED display devices.
In some embodiments of the present application, the graphene material may be prepared using a redox method, which includes the steps of: and (3) reacting natural Graphite with an oxidant to generate Graphite Oxide (GO), preparing single-layer Graphite oxide after ultrasonic dispersion, and adding a reducing agent to remove oxygen-containing groups on the surface of the Graphite oxide to obtain the graphene material. Wherein the oxidizing agent comprises a strong oxidizing substance and a strong acid. The strongly oxidizing substance includes: potassium permanganate, hydrogen peroxide or KClO 4 . The strong acid includes: concentrated sulfuric acid or fuming HNO 3 . The reducing agent comprises: dimethylhydrazine, hydrazine hydrate, sodium borohydride or hydroiodic acid. Oxygen-containing groups include carboxyl, epoxy, and hydroxyl groups.
In some embodiments of the present application, in order to improve the injection efficiency of carriers (such as electrons, etc.), a material with a lower work function should be selected as the cathode. In a metal cathode, the work function of silver is typically 4.26eV, and the work function of al is typically 4.3eV, so it is necessary to further lower the work function of the cathode, so the above-described embodiments of the present application adjust the work function of the graphene sheet layer to any one of values from 2.5eV to 3 eV. Therefore, the work function of the prepared graphene cathode is smaller than that of the current metal electrode or metal alloy electrode, and the injection efficiency of carriers is higher.
Some embodiments of the present application also provide a method for preparing a cathode for an organic top light emitting diode, which includes the steps of:
(1) Preparing a graphene material by adopting a redox method;
(2) Depositing a graphene material on the surface of the dielectric layer to obtain a graphene laminated layer formed by stacking a plurality of graphene sheets, wherein the graphene laminated layer is used as a cathode of the organic light-emitting diode; the type of dielectric layer may be tailored to the specific deposition purpose.
In the step (1), graphene materials are prepared by adopting a redox method, and the preparation method comprises the following steps: and (3) reacting natural Graphite with an oxidant to generate Graphite Oxide (GO), preparing single-layer Graphite oxide after ultrasonic dispersion, and adding a reducing agent to remove oxygen-containing groups on the surface of the Graphite oxide to obtain the graphene material. The oxidizing agent includes a strong oxidizing substance and a strong acid. The strongly oxidizing substance includes: potassium permanganate, hydrogen peroxide or KClO 4 . The strong acid includes: concentrated sulfuric acid or fuming HNO 3 . The reducing agent comprises: dimethylhydrazine, hydrazine hydrate, sodium borohydride or hydroiodic acid. Oxygen-containing groups include carboxyl, epoxy, and hydroxyl groups.
In the step (2), the graphene material may be deposited by any one of a chemical vapor deposition method (Chemical vapor deposition method, CVD), an epitaxial growth method, a chemical lift-off method, a chemical synthesis method, and the like.
In the step (2), the organic light emitting diode may be a flexible organic top light emitting diode, a flexible organic bottom light emitting diode, a non-flexible organic top light emitting diode, a non-flexible organic bottom light emitting diode, or the like.
In step (2), the overall work function of the cathode is any one of 2.5eV to 3 eV.
Some embodiments of the present application also provide an organic top light emitting diode. Referring to fig. 1, the organic top light emitting diode in the above embodiment includes the following structure: a substrate, an anode layer (anode layer), a hole injection layer (Hole injection layer, HIL), a hole transport layer (Hole tranport layer, HTL), a light Emitting layer (EML), an electron transport layer (Electron transport layer, ETL), a cathode layer (cathode layer), a Capping layer (CPL), and a cover glass layer (cover glass) are sequentially disposed from bottom to top. Cover glass layers (cover glass) are part of the package structure.
In some embodiments of the present application, the cathode layer is a graphene stack of multiple graphene sheets stacked. The thickness of each graphene sheet layer ranges from any one value from 0.332nm to 0.357 nm. The number of layers formed by stacking graphene sheets is any integer from 35 layers to 55 layers. The work function of the cathode is any one of 2.5eV to 3 eV.
In some embodiments of the present application, the thickness of the anode layer may be any value in the range of 25nm to 55nm, may be any value in the range of 30nm to 50nm, may be any value in the range of 35nm to 45nm, or may be 40nm. Since the cathode in the above embodiment is a graphene cathode having a stacked structure, the thickness thereof is any one of 15nm to 20 nm. In order to match the graphene cathode so as to effectively combine electrons and holes in the light-emitting layer, the thickness of the anode layer needs to be correspondingly adjusted to match the thickness of the graphene cathode, so the thickness of the anode layer is adjusted to be in the range of 25nm to 55nm in the above-mentioned embodiments.
In some embodiments of the present application, the hole injection layer may have a thickness ranging from 20nm to 40nm, from 23nm to 36nm, from 25nm to 35nm, from 27nm to 32nm, or from 28nm to 30 nm. The hole injection layer is used to reduce the hole injection barrier between the anode layer and the hole transport layer and to reduce interface defects, and therefore the thickness of the hole injection layer needs to be matched with that of the anode layer, so the above embodiments adjust the thickness of the hole injection layer to be in the range of 20nm to 40nm.
In some embodiments of the present application, the thickness of the hole transport layer may be any value from 15nm to 35nm, or from 19nm to 33nm, or from 21nm to 30nm, or from 25nm to 27 nm. The material of the optional hole transport layer may include Carbazole (Carbazole), diphenylamine (Diphenylamine), dimethylbenzidine (Ditolylamine), and the like.
In some embodiments of the present application, the thickness of the light emitting layer may be any value in the range of 12nm to 45nm, may be any value in the range of 15nm to 40nm, and may be any value in the range of 20nm to 35 nm. The thickness of the light-emitting layer needs to be matched to the thicknesses of the anode and cathode layers to allow efficient recombination of electrons and holes at the layer.
In some embodiments of the present application, the cathode layer is made of a graphene material, and the anode layer must not be made of the above-mentioned graphene material, otherwise the work functions of the cathode layer and the anode layer are the same, and it is difficult to achieve efficient recombination of carriers (electrons or holes) in the light emitting layer, so that it is difficult to ensure that the display device can achieve a desired display effect. In general, to lower the injection barrier of an OLED device, the work function of the cathode needs to be lower than the anode to match the LUMO and HOMO levels of the organic materials in the OLED device.
In some embodiments of the present application, the thickness of the electron transport layer may range from any value from 3nm to 15nm, from 5nm to 12nm, from 7nm to 11nm, and from 9nm to 10 nm.
Some embodiments of the present application also provide a method for preparing an organic top light emitting diode, which includes the following steps:
(1) Sequentially forming a substrate, an anode layer, a hole injection layer, a hole transport layer, a light emitting layer and an electron transport layer from bottom to top;
(2) Depositing graphene materials on the upper surface of the electron transport layer by layer in inert atmosphere, forming a graphene sheet layer every time one graphene sheet layer is deposited, and sequentially depositing a plurality of graphene sheets to obtain a cathode layer formed by stacking the graphene sheets;
(3) And forming a sealing layer on the cathode layer, and packaging to obtain the organic light-emitting diode.
In step (1), the electron transport layer may be formed by vapor deposition in a vapor deposition chamber. After the electron transport layer is formed, cathode preparation is performed.
In step (2), the inert atmosphere may be nitrogen, provided by a nitrogen tank.
In the step (2), the graphene material may be deposited by Chemical Vapor Deposition (CVD), and a Mask (Mask) is required to be used to evaporate the cathode. The multi-layered graphene sheets may be formed by a layer-by-layer evaporation method such that the thickness of each graphene sheet ranges from any one value from 0.332nm to 0.357nm, and stacked layer by layer so as to form a graphene stack having 35 to 55 layers, thereby forming a cathode layer having a thickness from 15nm to 20 nm. It is necessary to make the work function of the cathode layer any one of 2.5eV to 3 eV. In other embodiments of the present application, the deposition method of the graphene material is also not limited to Chemical Vapor Deposition (CVD).
In step (3), the capping layer is part of the final package structure. The capping layer is made of a material with a larger refractive index and a smaller light absorption coefficient, so as to improve the light emitting efficiency of the top-emitting OLED device from the cathode. If a material with a high reflectivity is used for the capping layer, it is difficult to emit light from the cathode. If the capping layer is made of a material having a high light absorption coefficient, the capping layer easily absorbs light from the light-emitting layer so as not to emit the cathode toward the cathode. The sealing layer can be formed by adopting an evaporation method, and after evaporation is finished, the sealing layer returns to the nitrogen box for dispensing and packaging.
In some embodiments of the present application, after encapsulation, the conductivity of the encapsulated top-emitting OLED display panel is tested as an example. Test results show that the conductivity of the top-emitting OLED display panel is superior to that of the prior artAn OLED display panel. This is because the cathode of the top-emission OLED display panel is a graphene cathode, and graphene has excellent conductivity and a smaller work function than a metal cathode, and thus the graphene cathode made of graphene has excellent conductivity. In addition, the graphene is of a lamellar structure, the two-dimensional structure of the single-layer graphene enables the graphene to have better light transmittance, and after 35 layers to 55 layers are laminated, detection proves that the graphene laminated layer still has good light transmittance. Presumably because the carbon atoms in graphene are in sp 2 The six carbon atoms are connected into a single-layer two-dimensional honeycomb lattice structure through hybridization connection, and even if the single-layer two-dimensional honeycomb lattice structure is stacked into a laminated structure, a large light transmission gap still exists between the honeycomb lattice structures, so that the graphene passes through a plurality of layers of laminated layers, and the light transmittance of the cathode manufactured by the graphene is still superior to that of a metal electrode or a metal alloy electrode. In addition, the graphene component has better folding performance, and the cathode of the display panel in the prior art is an all-metal electrode or a metal alloy electrode with higher hardness, so that the folding performance of the top-light-emitting OLED display panel in the embodiment of the application is superior to that of the display panel in the prior art, and the display panel can be used for a flexible display panel. In addition, the stability of the graphene is superior to that of metal, and even if the packaging layer is damaged, the graphene is not easy to be attacked by water and oxygen to be oxidized, so that the service life of the graphene is obviously longer than that of a metal cathode. In summary, the above embodiments of the present application can solve the problems of poor light transmittance, poor conductivity, or poor stability due to easy oxidation of a metal cathode or a metal alloy cathode in a Top OLED device.
The above-described embodiments of the present application may be combined arbitrarily, and new embodiments may be formed without inventive effort.
The foregoing has outlined rather broadly the more detailed description of the embodiments of the present application, wherein the detailed description has been presented for the purpose of providing a better understanding of the principles and embodiments of the present application, and wherein the detailed description is merely intended to facilitate the understanding of the method and concepts of the present application; meanwhile, as those skilled in the art will vary in the specific embodiments and application scope according to the ideas of the present application, the contents of the present specification should not be construed as limiting the present application in summary.
Claims (10)
1. The cathode for the organic light-emitting diode is characterized in that the cathode is a graphene laminated layer formed by stacking a plurality of graphene sheets, the thickness of each graphene sheet is any one value ranging from 0.332nm to 0.357nm, the number of layers formed by stacking the graphene sheets is any integer ranging from 35 layers to 55 layers, and the work function of the cathode is any one value ranging from 2.5eV to 3 eV.
2. The cathode for an organic light emitting diode according to claim 1, wherein the thickness of the cathode is selected from any one of values of 15nm to 20 nm.
3. A method for preparing a cathode for an organic light emitting diode, comprising the steps of:
preparing a graphene material by adopting an oxidation-reduction method;
depositing the graphene material to obtain a graphene laminated layer formed by stacking a plurality of graphene sheets, wherein the graphene laminated layer is used as a cathode of the organic light-emitting diode;
the thickness of each graphene sheet layer ranges from 0.332nm to 0.357nm, the number of layers formed by stacking the graphene sheet layers is an integer from 35 layers to 55 layers, and the work function of the cathode is an integer from 2.5eV to 3 eV.
4. A method of preparing a graphene material according to claim 3, comprising the steps of: and (3) reacting natural graphite with an oxidant to generate graphite oxide, preparing single-layer graphite oxide after ultrasonic dispersion, and adding a reducing agent to remove oxygen-containing groups on the surface of the single-layer graphite oxide to obtain the graphene material.
5. The method of claim 4, wherein the oxidizing agentIncluding strong oxidizing substances and strong acids; the strongly oxidizing substance includes: potassium permanganate, hydrogen peroxide or KClO 4 The method comprises the steps of carrying out a first treatment on the surface of the The strong acid comprises: concentrated sulfuric acid or fuming HNO 3 The method comprises the steps of carrying out a first treatment on the surface of the And/or
The reducing agent comprises: dimethylhydrazine, hydrazine hydrate, sodium borohydride or hydroiodic acid; and/or
The oxygen-containing groups include carboxyl, epoxy and hydroxyl groups.
6. The method according to claim 5, wherein the thickness of the cathode is selected from any one of 15nm to 20 nm.
7. An organic light emitting diode, comprising: the device comprises a substrate, an anode layer, a hole injection layer, a hole transport layer, a light emitting layer, an electron transport layer, a cathode layer and a sealing layer which are sequentially arranged from bottom to top;
the cathode layer is a graphene lamination formed by stacking a plurality of graphene sheets, the thickness of each graphene sheet is any numerical value ranging from 0.332nm to 0.357nm, the number of layers formed by stacking the graphene sheets is any integer ranging from 35 layers to 55 layers, and the work function of the cathode is any numerical value ranging from 2.5eV to 3 eV.
8. The organic light-emitting diode according to claim 7, wherein the thickness of the anode layer is any one of values in a range of 25nm to 55 nm; and/or
The thickness of the hole injection layer ranges from 20nm to 40 nm; and/or
The thickness of the hole transport layer ranges from 15nm to 35 nm; and/or
The thickness of the light-emitting layer is any one value in the range of 12nm to 45 nm; and/or
The thickness of the electron transport layer ranges from 3nm to 15 nm; and/or
The thickness of the cathode layer is selected from any one of values from 15nm to 20 nm.
9. The preparation method of the organic light-emitting diode is characterized by comprising the following steps of:
sequentially forming a substrate, an anode layer, a hole injection layer, a hole transport layer, a light emitting layer and an electron transport layer from bottom to top;
in an inert atmosphere, depositing graphene materials on the upper surface of the electron transport layer by layer, forming a graphene sheet layer every time one graphene sheet layer is deposited, and sequentially depositing a plurality of graphene sheets to obtain a cathode layer formed by stacking the graphene sheets;
forming a sealing layer on the cathode layer, and packaging to obtain an organic light-emitting diode;
the thickness of each graphene sheet layer ranges from 0.332nm to 0.357nm, the number of layers formed by stacking the graphene sheet layers is an integer from 35 layers to 55 layers, and the work function of the cathode layer is an integer from 2.5eV to 3 eV.
10. The method according to claim 9, wherein the thickness of the cathode is selected from any one of 15nm to 20 nm.
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