Organic light-emitting device, preparation method thereof, and display device

Abstract

An organic light-emitting device and display device solve the poor stability problem of organic light-emitting devices in the prior art. The organic light-emitting device includes a first functional layer, a crosslinking layer, and a second functional layer stacked in sequence. The first functional layer and the second functional layer have an energy level difference, and the crosslinking layer includes a crosslinking material.

Description

Technical Field

[0001] The present application relates to the technical field of light-emitting devices, and in particular to an organic light-emitting device, a preparation method thereof, and a display device. Background Art

[0002] Organic light-emitting diodes (OLEDs) have gradually gained a foothold in the display industry thanks to their advantages such as lightness, flexibility, high contrast, and wide color gamut. However, because OLEDs are mostly composed of organic materials, their properties are easily affected by conditions such as high temperature, high humidity, and light, resulting in poor device stability. Summary of the Invention

[0003] In view of this, embodiments of the present application provide an organic light-emitting device, a method for preparing the same, and a display device to solve the problem of poor stability of organic light-emitting devices in the prior art.

[0004] In a first aspect, the present application provides an organic light-emitting device, comprising a first functional layer, a cross-linking layer, and a second functional layer stacked in sequence, wherein there is an energy level difference between the first functional layer and the second functional layer, and the cross-linking layer comprises a cross-linking material.

[0005] In one embodiment, the first functional layer includes a first material, and the second functional layer includes a second material; the cross-linked material is obtained by a cross-linking reaction between a first derivative of the first material and a second derivative of the second material.

[0006] In one embodiment, the first derivative and the second derivative each include a photo-crosslinking group.

[0007] In one embodiment, the first functional layer further includes a third material, and the volume ratio of the third material in the first functional layer is less than or equal to the first material.

[0008] In one embodiment, the volume ratio of the cross-linking material in the cross-linking layer is 20%-100%, and the thickness of the cross-linking layer is greater than or equal to 5 angstroms and less than or equal to 50 angstroms.

[0009] In one embodiment, the first functional layer and the second functional layer are respectively selected from any two adjacent items of a hole injection layer, a hole transport layer, a light emitting layer, an electron transport layer, and an electron injection layer.

[0010] A second aspect of the present application provides a display device comprising the organic light-emitting device provided by any of the above embodiments.

[0011] The third aspect of the present application provides a method for preparing an organic light-emitting device, comprising: preparing a cross-linked layer on a first functional layer, the cross-linked layer comprising a cross-linked material; preparing a second functional layer on the cross-linked layer, and there is an energy level difference between the first functional layer and the second functional layer.

[0012] In one embodiment, the first functional layer includes a first material, and the second functional layer includes a second material; preparing a cross-linked layer on the first functional layer includes: vapor-depositing a composite material layer on the first functional layer, the composite material layer including a first derivative of the first material and a second derivative of the second material, the first derivative and the second derivative including the same photo-cross-linking group; irradiating the composite material layer with an ultraviolet wavelength to cause a cross-linking reaction between the first derivative and the second derivative to obtain a cross-linked layer.

[0013] In one embodiment, the ultraviolet wavelength is greater than or equal to 320 nm and less than or equal to 400 nm, and the intensity is greater than or equal to 10 mW / cm 2 and less than or equal to 1000mW / cm 2 , the irradiation time is greater than or equal to 1 min and less than or equal to 30 min.

[0014] According to the organic light-emitting device, preparation method thereof, and display device provided in the present application, a cross-linking layer is provided between adjacent functional layers. Since the cross-linking material has high stability, the properties will not change due to heat, thereby improving the stability of the organic light-emitting device. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 This is a schematic structural diagram of the organic light-emitting device provided in the first embodiment of the present application.

[0016] Figure 2 This is a schematic structural diagram of the organic light-emitting device provided in the second embodiment of the present application.

[0017] Figure 3 This is a schematic structural diagram of the organic light-emitting device provided in the third embodiment of the present application.

[0018] Figure 4 Shown is a flow chart of the preparation process of an organic light-emitting device provided in one embodiment of the present application. DETAILED DESCRIPTION

[0019] The following will be combined with the drawings in the embodiments of this application to clearly and completely describe the technical solutions in the embodiments of this application. Obviously, the embodiments described are only part of the embodiments of this application, not all of the embodiments. Based on the embodiments in this application, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of this application.

[0020] Figure 1 This is a schematic diagram of the structure of an organic light-emitting device provided in the first embodiment of the present application. The organic light-emitting device is, for example, an organic light-emitting diode. The organic light-emitting device 10 includes an anode 11, a cathode 17, and a plurality of functional layers located between the anode 11 and the cathode 17. Specifically, Figure 1As shown, the organic light-emitting device 10 includes an anode 11, a hole injection layer 12, a hole transport layer 13, a light-emitting layer 14, an electron transport layer 15, an electron injection layer 16 and a cathode 17 stacked in sequence.

[0021] Anode 11 is used to inject holes, hole injection layer 12 is used to inject holes from anode 11 into the OLED device, and hole transport layer 13 is used to transport holes injected into the OLED by hole injection layer 12 to light-emitting layer 14. Cathode 17 is used to inject electrons, electron injection layer 16 is used to inject electrons into the OLED device, and electron transport layer 15 is used to transport electrons injected into the OLED by electron injection layer 16 to light-emitting layer 14. Electrons and holes recombine in light-emitting layer 14, and the energy released during the recombination process is transferred to the light-emitting material, causing the light-emitting material to be excited to an excited state. The light-emitting material then spontaneously returns to the ground state from the excited state, emitting light through radiative transition.

[0022] Among them, the anode 11 can be a transparent or non-transparent electrode, including but not limited to metal or metal oxide. In one example, the anode is formed by coating a layer of indium tin oxide on a glass substrate. The hole injection layer 12 includes a matrix material and a dopant doped in the matrix material. The matrix material is a polymer host, the surface energy of the dopant is lower than the surface energy of the matrix material, and the ionization potential of the dopant is higher than the ionization potential of the matrix material. In one example, the matrix material is a mixed material of poly(3,4-ethylenedioxythiophene) and polystyrene sulfonate (PEDOT:PSS), and the dopant is any one of polystyrene sulfonic acid, a derivative of polystyrene sulfonic acid, or a chlorine-containing metal inorganic salt. The hole transport layer 13 includes but is not limited to organic small molecule materials, such as 4,4',4"-tris(carbazol-9-yl)triphenylamine (TCTA). The light-emitting layer 14 includes but is not limited to a host-guest doping material system, and the material of the light-emitting layer 14 can be di[2-((oxy)diphenylphosphino)phenyl]ether (DPEPO):bis[4-(9,9-dimethyl-9,10-dihydroacridinium)phenyl]sulfone (DMAC-DPS). The electron injection layer 16 includes but is not limited to organic small molecule materials. The electron transport layer 15 includes but is not limited to organic small molecule materials, and the material of the electron transport layer 15 can be 1,3,5-tris(3-(3-pyridyl)phenyl)benzene (Tm3PyPB). The cathode 17 is a transparent or non-transparent cathode, including but not limited to a transparent metal electrode, and can also be a metal alloy electrode. In one example, the material of the cathode 17 can be lithium fluoride / aluminum.

[0023] Figure 1 For illustration only, Figure 1The functional layers in the illustrated organic light-emitting device 10 may be increased or decreased. For example, a hole blocking layer may be provided between the light-emitting layer 14 and the electron transport layer 15. Another example is an electron blocking layer may be provided between the light-emitting layer 14 and the hole transport layer 13. The layers mentioned in this embodiment are merely intended to illustrate the relative stacking relationships of the functional components and do not limit their specific shapes or sizes. For example, these layers do not necessarily have to be uniform in thickness.

[0024] The inventors discovered that Figure 1 In the organic light-emitting device 10 shown in the figure, a heterojunction is formed between two adjacent functional layers, resulting in an energy level difference and a potential barrier. When lit, heat is generated at the heterojunction, causing changes in the material properties at the interface and affecting the stability of the device.

[0025] In view of this, the present application provides an organic light-emitting device, a preparation method thereof, and a display device. By setting a cross-linking layer between adjacent functional layers and utilizing the stability of the cross-linking material, the problem of the material properties at the interface between adjacent functional layers being easily affected by external conditions, thereby avoiding the problem of poor device stability.

[0026] The structure of the organic light-emitting device is described in detail below with reference to the accompanying drawings.

[0027] Figure 2 This is a schematic diagram of the structure of the organic light-emitting device provided in the second embodiment of the present application. Figure 2 As shown, the organic light emitting device 20 and Figure 1 The difference of the organic light emitting device 10 is that it further comprises a cross-linking layer 21, which comprises a cross-linking material. The cross-linking layer 23 is located at Figure 1 Between any two adjacent film layers of the organic light-emitting device 10 shown.

[0028] Specifically, if Figure 2 As shown, the organic light-emitting device 20 includes a first functional layer 22, a crosslinking layer 21, and a second functional layer 23 stacked in sequence. There is an energy level difference between the first functional layer 22 and the second functional layer 23. In one example, the first functional layer 22 is a light-emitting layer, and the second functional layer 23 is a hole transport layer or an electron transport layer. In another example, the first functional layer 22 is a hole transport layer, and the second functional layer 23 is a light-emitting layer or a hole injection layer. In yet another example, the first functional layer 22 is an electron transport layer, and the second functional layer 23 is an electron injection layer or a light-emitting layer.

[0029] A cross-linked material refers to a material obtained through a cross-linking reaction. A cross-linking reaction is a reaction in which two or more molecules (generally linear molecules) bond and cross-link to form a relatively stable molecule (bulk molecule) network structure. This reaction transforms linear or slightly branched macromolecules into a three-dimensional network structure. The cross-linked material has properties such as high strength, heat resistance, wear resistance, and solvent resistance, thereby avoiding the problem of material properties between the first functional layer 22 and the second functional layer 23 being easily changed when the light is on, thereby improving the stability of the organic light-emitting device.

[0030] In this embodiment, the first functional layer 22 comprises a first material, and the second functional layer 23 comprises a second material. The cross-linked material is formed by a cross-linking reaction between a derivative of the first material and a derivative of the second material. In this case, the energy level of the cross-linked layer 21 lies between the energy levels of the first and second functional layers 22, 23, thereby providing an energy transition. This reduces heat generation between the first and second functional layers 22, 23 during lighting, further enhancing the stability of the organic light-emitting device.

[0031] In one embodiment, the derivative of the first material and the derivative of the second material each include a photocrosslinking group. For example, the derivative of the first material and the derivative of the second material each include the same photocrosslinking group. The photocrosslinking group is, for example, any one of a vinyl group, a styryl allyl group, a vinyl carbazole group, an acrylate group, coumarin and its derivatives, a chalcone and its derivatives, and a benzoin and its derivatives. In this case, the crosslinking material is obtained by a photocrosslinking reaction of the derivative of the first material and the derivative of the second material. For an organic light-emitting device, the use of a photocrosslinking reaction to prepare a crosslinked layer can ensure that the crosslinked layer has a better film-forming effect than other crosslinking methods, such as thermal crosslinking. For details, see the following embodiment of the preparation method of an organic light-emitting device.

[0032] In one embodiment, the first functional layer 22 further comprises a third material, and the volume ratio of the third material in the first functional layer 22 is less than or equal to that of the first material. That is, when the first functional layer 22 is a mixed material composed of at least two materials, a derivative of the material with a larger volume ratio is selected so that it is cross-linked with the second material of the second functional layer 23 to form a cross-linked material. For example, the first functional layer 22 is a light-emitting layer, which includes a host material and a guest material, and the guest material is used to receive energy from the host material and convert it into light energy. The volume ratio of the host material is greater than that of the guest material. A derivative of the host material is selected so that it is cross-linked with the second material of the second functional layer 23 to form a cross-linked material. For another example, the first functional layer 22 is a hole transport layer, which includes a matrix material and a dopant, and the volume ratio of the matrix material is greater than that of the dopant. A derivative of the matrix material is selected so that it is cross-linked with the second material of the second functional layer 23 to form a cross-linked material.

[0033] In this way, by selecting a derivative of a material with a larger volume ratio in the first functional layer 22, it is cross-linked with the second material of the second functional layer 23 to form a cross-linked material, so that the material properties of the cross-linked layer 21 and the first functional layer 22 are closer, and the energy level difference between the cross-linked layer 21 and the first functional layer 22 is made smaller, thereby reducing the heat generated at the interface between the cross-linked layer 21 and the first functional layer 22 in the lit state, and further improving the reliability of the device.

[0034] In one embodiment, the volume ratio of the cross-linked material in the cross-linked layer 21 is 20%-100%, and the thickness of the cross-linked layer 21 is greater than or equal to 5 angstroms and less than or equal to 50 angstroms. For example, the volume ratio of the cross-linked material in the cross-linked layer 21 is 30%, 35%, 40%, 50%, etc. The thickness of the cross-linked layer 21 is 10 angstroms, 15 angstroms, 25 angstroms, 35 angstroms, etc. In this case, because the cross-linked material is discretely distributed over any unit thickness of the cross-linked layer 21, that is, the cross-linked material does not form a complete layer structure, and at the same time, the overall thickness of the cross-linked layer 21 is moderate, even if the cross-linked molecular structure affects the material's transport properties, carriers can still be transported through the tunneling mechanism without affecting the electrical properties of the overall device.

[0035] When the volume ratio of the cross-linking material in the cross-linking layer 21 is less than 100%, the cross-linking layer 21 may further include at least one of a third derivative of the first material of the first functional layer 22 and a fourth derivative of the second material of the second functional layer 23. That is, in addition to the cross-linking material, the cross-linking layer 21 also includes the third derivative of the first material of the first functional layer 22 and / or the fourth derivative of the second material of the second functional layer 23. Neither the third derivative nor the fourth derivative contains a cross-linking group and cannot undergo a cross-linking reaction. Compared to the cross-linking material, the third derivative has material properties closer to those of the first functional layer 22, and the fourth derivative has material properties closer to those of the second functional layer 23. Therefore, by configuring the cross-linking layer 21 to include not only the cross-linking material but also the third and fourth derivatives, the material properties per unit thickness of the cross-linking layer 21 can be made closer to those of the first and second functional layers 22 and 23, thereby further reducing the energy level difference.

[0036] Figure 3 This is a schematic diagram of the structure of the organic light-emitting device provided in the third embodiment of the present application. Figure 3 As shown, the organic light emitting device 30 includes a plurality of cross-linked layers 21, the plurality of cross-linked layers 21 are respectively located at Figure 1 Between two adjacent functional layers shown. For example, Figure 3As shown, the organic light-emitting device 30 includes an anode 11, a hole injection layer 12, a first cross-linked layer 31, a hole transport layer 13, a second cross-linked layer 32, a light-emitting layer 14, a third cross-linked layer 33, an electron transport layer 15, a fourth cross-linked layer 34, an electron injection layer 16, and a cathode 17, which are stacked in sequence. It should be understood that the terms "first," "second," "third," and "fourth" mentioned herein are for ease of description only and are not intended to be limiting.

[0037] Each crosslinked layer includes a crosslinked material, which is formed by a crosslinking reaction between derivatives of materials contained in the two film layers in contact with the crosslinked layer. For example, the crosslinked material of the first crosslinked layer 31 is formed by a crosslinking reaction between a derivative of the material contained in the hole injection layer 12 and a derivative of the material contained in the hole transport layer 13. The crosslinked material of the second crosslinked layer 32 is formed by a crosslinking reaction between a derivative of the material contained in the hole transport layer 13 and a derivative of the material contained in the light-emitting layer 14. The same applies to the crosslinked materials of the third crosslinked layer 33 and the fourth crosslinked layer 34.

[0038] Specific technical details of any cross-linked layer can be found in Figure 2 The embodiments shown will not be described in detail here.

[0039] It should be noted that, in the organic light-emitting device, the number and specific positions of the cross-linked layers can be reasonably set according to actual needs.

[0040] This application also provides a method for preparing an organic light-emitting device. Figure 4 The figure shows a flow chart of the preparation process of an organic light-emitting device provided in one embodiment of the present application. Figure 4 As shown, the preparation method 400 includes:

[0041] Step S410 , preparing a cross-linking layer on the first functional layer, wherein the cross-linking layer includes a cross-linking material.

[0042] Step S420: preparing a second functional layer on the cross-linked layer, wherein the second functional layer has an energy level difference with the first functional layer.

[0043] Due to the energy level difference between the second functional layer and the first functional layer, heat is generated between the first and second functional layers during lighting. By adding a cross-linking material, the stability of the organic light-emitting device is improved by preventing thermal property changes due to the cross-linking material's high stability.

[0044] In one embodiment, the first functional layer includes a first material, and the second functional layer includes a second material. In this case, step S410 is specifically performed as follows:

[0045] First, a composite material is vapor-deposited on the first functional layer. The composite material includes a derivative of a first material and a second derivative of a second material, wherein the first and second derivatives include the same photocrosslinking group. In one embodiment, the composite material further includes a third derivative of the first material and / or a fourth derivative of the second material, wherein neither the third derivative nor the fourth derivative includes a photocrosslinking group and cannot undergo a photocrosslinking reaction.

[0046] Next, the composite material layer is irradiated with ultraviolet light to induce a cross-linking reaction between the first and second derivatives, forming a cross-linked layer. Because the photocrosslinking step precedes a high-temperature evaporation process, thermal crosslinking would cause cross-linking to occur simultaneously with evaporation, affecting film formation. Therefore, this embodiment utilizes photocrosslinking to ensure a superior film formation of the cross-linked layer.

[0047] In one embodiment, the ultraviolet wavelength is greater than or equal to 320 nm and less than or equal to 400 nm, and the intensity is greater than or equal to 10 mW / cm 2 and less than or equal to 1000mW / cm 2 The irradiation time is greater than or equal to 1 minute and less than or equal to 30 minutes. In this way, on the one hand, the formation of the cross-linked layer is guaranteed, and on the other hand, other layers are protected from severe cracking due to ultraviolet irradiation.

[0048] The method for preparing an organic light-emitting device provided in any embodiment of the present application can be used to prepare the organic light-emitting device provided in any of the above embodiments. Details not described in the preparation method embodiment can be referred to the organic light-emitting device embodiment and will not be repeated here.

[0049] The above description has been provided for the purpose of illustration and description. In addition, this description is not intended to limit the embodiments of the present application to the forms disclosed herein. Although a number of example aspects and embodiments have been discussed above, those skilled in the art will recognize certain variations, modifications, alterations, additions, and sub-combinations thereof.

Claims

1. An organic light-emitting device, characterized in that: The method comprises a first functional layer, a cross-linked layer, and a second functional layer stacked in sequence, wherein the first functional layer and the second functional layer have an energy level difference, and the cross-linked layer comprises a cross-linked material; The first functional layer comprises a first material, and the second functional layer comprises a second material; the cross-linked material is obtained by a cross-linking reaction between a first derivative of the first material and a second derivative of the second material; and the energy level of the cross-linked layer is between that of the first functional layer and the second functional layer; Wherein, the first derivative and the second derivative respectively include a photo-crosslinking group.

2. The organic light-emitting device according to claim 1, wherein The first functional layer further includes a third material, and a volume ratio of the third material in the first functional layer is less than or equal to that of the first material.

3. The organic light-emitting device according to claim 1, wherein The volume ratio of the cross-linking material in the cross-linking layer is 20%-100%, and the thickness of the cross-linking layer is greater than or equal to 5 angstroms and less than or equal to 50 angstroms.

4. The organic light-emitting device according to claim 1, wherein The first functional layer and the second functional layer are respectively selected from any two adjacent items of a hole injection layer, a hole transport layer, a light emitting layer, an electron transport layer, and an electron injection layer.

5. A display device, characterized in that: The organic light-emitting device comprises any one of claims 1 to 4.

6. A method for preparing an organic light-emitting device, characterized in that: include: preparing a cross-linked layer on the first functional layer, wherein the cross-linked layer comprises a cross-linked material; preparing a second functional layer on the cross-linked layer, wherein there is an energy level difference between the first functional layer and the second functional layer; Wherein, the first functional layer comprises a first material, and the second functional layer comprises a second material; and preparing a cross-linked layer on the first functional layer comprises: Depositing a composite material layer on the first functional layer, wherein the composite material layer includes a first derivative of the first material and a second derivative of the second material, wherein the first derivative and the second derivative include the same photocrosslinking group; irradiating the composite material layer with ultraviolet wavelength to cause a cross-linking reaction between the first derivative and the second derivative to obtain the cross-linked layer; The ultraviolet wavelength is greater than or equal to 320 nm and less than or equal to 400 nm, the intensity is greater than or equal to 10 mW / cm2 and less than or equal to 1000 mW / cm2, and the irradiation time is greater than or equal to 1 min and less than or equal to 30 min.

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