A charge generation structure, a preparation method thereof, and a light-emitting device

Abstract

The present invention discloses a charge generation structure, a preparation method thereof, and a light-emitting device, belonging to the field of organic electroluminescence. The charge generation structure includes a first organic layer and a second organic layer. The first organic layer is a crystalline material with electron transport characteristics, and the second organic layer is a crystalline material with hole transport characteristics. The interface roughness between the first organic layer and the second organic layer is 10 nm to 100 nm. By providing the first organic layer and the second organic layer with crystalline characteristics, the contact area of the charge generation interface can be effectively increased, thereby increasing the amount of charge generated. This not only effectively reduces the voltage of the organic electroluminescent device, but also significantly improves the efficiency and stability of the organic electroluminescent device.

Description

Technical Field

[0001] The present invention belongs to the field of organic electroluminescence, and particularly relates to a charge generation structure, a preparation method thereof, and a light-emitting device. Background Art

[0002] An organic light-emitting diode (OLED) sequentially includes a substrate (7), a first electrode, an organic layer, and a second electrode according to its structure. At least one of the first electrode and the second electrode is made of a transparent or semi-transparent material. The first electrode is a transparent or semi-transparent electrode layer, which is the structure of a bottom-emitting device, and the second electrode layer (4) can be formed into a reflective electrode layer; the second electrode is a transparent or semi-transparent electrode layer, which is the structure of a top-emitting device, and the first electrode layer can be formed into a reflective electrode layer. Electrons (electron) and holes (hole) injected into the electrode layer recombine (recombination) in the light-emitting layer of the organic layer to generate photons.

[0003] In an OLED device, if only a single-layer device is used, to achieve a higher brightness, the heat will surge due to an excessive driving current, affecting the performance and lifespan of the device. A stacked OLED device is to connect two or more light-emitting units in series through a charge generation structure (connection layer), thereby improving the current efficiency, extending the lifespan of the device, and meeting the brightness requirements for lighting use.

[0004] The charge generation structure is a key component of a stacked OLED device. It needs to provide electrons and holes to adjacent light-emitting units simultaneously. Therefore, the charge generation structure has a direct impact on the efficiency of the stacked OLED device.

[0005] CN 106711343 A discloses a charge generation structure, a preparation method thereof, and an application. The charge generation structure includes a first film layer and a second film layer stacked on top of each other. The interface roughness between the first film layer and the layer is

[0006] 0.1 nm to 50 nm. The rough interface design effectively increases the contact area between the first film layer and the second film layer and increases the bonding force between the film layers. It can not only generate more carriers but also achieve efficient carrier injection, effectively improving the efficiency and lifespan of the device using it. The preparation method of the charge generation structure has a simple process, low precision requirements, and low cost. The material of the present invention is an induced crystallization material, that is, the crystallization of the second film layer is realized through the induction of the first organic layer, further increasing the contact area of the hole and electron separation interface to achieve the separation of more electrons and holes, not only effectively reducing the voltage of the device but also greatly improving the efficiency of the device. Summary of the Invention

[0007] In view of the problems existing in the prior art, the present invention provides a high-performance charge generation structure and a preparation method thereof, which can not only effectively reduce the voltage of an organic electroluminescent device, but also significantly improve the efficiency and stability of the organic electroluminescent device.

[0008] To solve the above technical problems, the technical solution adopted by the present invention is as follows:

[0009] A charge generation structure according to the present invention includes a first organic layer and a second organic layer. The first organic layer is a crystalline material with electron transport characteristics and / or the second organic layer is a crystalline material with hole transport characteristics. The interface roughness between the first organic layer and the second organic layer is 10 nm to 100 nm.

[0010] Optionally, the material of the first organic layer is pentacene and its derivative materials, and the second organic material is copper phthalocyanine fluoride materials.

[0011] Optionally, the thickness of the first organic layer is 1 nm to 100 nm, and the thickness of the second organic layer is 1 nm to 100 nm.

[0012] Optionally, the LUMO energy level of the first organic layer is greater than the LUMO energy level of the second organic layer, and the HOMO energy level of the second organic layer is less than the HOMO energy level of the first organic layer.

[0013] Optionally, the difference between the LUMO energy level of the first organic layer and the LUMO energy level of the second organic layer is greater than or equal to 1.5 eV, and the difference between the HOMO energy level of the second organic layer and the HOMO energy level of the first organic layer is greater than or equal to 1.5 eV.

[0014] Optionally, a third film layer is further included between the first organic layer and the second organic layer. The LUMO energy level of the third film layer is greater than the LUMO energy level of the first organic layer; the HOMO energy level of the third film layer is less than or equal to the HOMO energy level of the first organic layer and greater than or equal to the HOMO energy level of the second organic layer; the difference between the LUMO energy level of the third film layer and the LUMO energy level of the first organic layer is greater than or equal to 0.5 eV; the glass transition temperature of the third film layer is greater than 120 °C.

[0015] Optionally, the third film layer is at least one of MoO 3 , V 2 O 5 , WO 3 , ReO 3 , NPB.

[0016] The preparation method of the charge generation structure described in the present invention includes the following steps:

[0017] Form a first organic layer by vacuum evaporation or spin coating. After preparation, heat the first organic layer to 80 - 120 °C and then cool it to room temperature; and / or, form a second organic layer by vacuum evaporation or spin coating. After preparation, heat the second organic layer to 80 - 120 °C and then cool it to room temperature.

[0018] Optionally, after the first organic layer is cooled to room temperature, a third film layer is prepared by vacuum evaporation or spin coating.

[0019] Optionally, the difference in interfacial roughness between the first organic layer and / or the second organic layer before heating and after cooling is greater than or equal to 10 nm.

[0020] The present invention also provides a light-emitting device, including at least two stacked light-emitting units and a charge generation structure disposed between adjacent light-emitting units.

[0021] The above technical solutions of the present invention have the following advantages compared with the prior art: 1. The charge generation structure of the present invention includes a first organic layer and a second organic layer. The first organic layer is a crystalline material with electron-transporting properties and the second organic layer is a crystalline material with hole-transporting properties. The interfacial roughness between the first organic layer and the second organic layer is 10 nm - 100 nm. By setting the first organic layer and the second organic layer with crystalline properties, the contact area of the charge generation interface can be effectively increased, thereby increasing the amount of charge generation. This not only effectively reduces the voltage of the organic electroluminescent device but also significantly improves the efficiency and stability of the organic electroluminescent device. 2. The present invention provides a third film layer. The three-layer structure can achieve rapid separation of electrons and holes, preventing exciton quenching caused by the aggregation of electrons and holes, so as to play a role in increasing the efficiency. 3. The preparation method of a charge generation structure described in the present invention has a simple process, low precision requirements, and low cost. Description of the Drawings

[0022] In order to make the content of the present invention easier to be clearly understood, the following further details the present invention according to specific embodiments of the present invention in conjunction with the drawings, where

[0023] Figure 1 is a schematic structural diagram of the charge generation structure described in Embodiment 1 of the present invention;

[0024] Figure 2 is a schematic structural diagram of the light-emitting device described in the embodiments of the present invention;

[0025] Figure 3 is a schematic structural diagram of the charge generation structure described in Embodiment 2 of the present invention. Detailed implementation manners

[0026] To make the objectives, technical solutions and advantages of the present invention clearer, the implementation manners of the present invention will be further described in detail below with reference to the accompanying drawings.

[0027] The present invention can be implemented in many different forms and should not be construed as limited to the embodiments set forth herein. On the contrary, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the concept of the present invention to those skilled in the art. The present invention will only be defined by the claims. In the drawings, the dimensions and relative dimensions of layers and regions are exaggerated for clarity. It should be understood that when an element such as a layer, region or substrate is referred to as being "formed on" or "disposed on" another element "above", the element can be directly disposed on the other element, or an intermediate element may also be present. On the contrary, when an element is referred to as being "directly formed on" or "directly disposed on" another element, there is no intermediate element.

[0028] A charge generation structure according to the present invention includes a first organic layer and a second organic layer. The first organic layer is a crystalline material having electron transport characteristics and / or the second organic layer is a crystalline material having hole transport characteristics. The interfacial roughness between the first organic layer and the second organic layer is 10 nm to 100 nm.

[0029] Optionally, the material of the first organic layer is pentacene and its derivative materials, and the second organic material is copper phthalocyanine fluoride materials, including copper tetrafluorophthalocyanine, copper octafluorophthalocyanine, copper hexadecafluorophthalocyanine, copper perfluorophthalocyanine and other materials, or it can also be copper phthalocyanine. The first organic layer 11 having crystalline characteristics and electron transport ability and the second organic layer 12 having crystalline characteristics and hole transport ability are both within the protection scope of the present invention.

[0030] Optionally, the thickness of the first organic layer is 1 nm to 100 nm, and the thickness of the second organic layer is 1 nm to 100 nm.

[0031] Optionally, the LUMO energy level of the first organic layer is greater than the LUMO energy level of the second organic layer, and the HOMO energy level of the second organic layer is less than the HOMO energy level of the first organic layer.

[0032] Optionally, the difference between the LUMO energy level of the first organic layer and the LUMO energy level of the second organic layer is greater than or equal to 1.5 eV, and the difference between the HOMO energy level of the second organic layer and the HOMO energy level of the first organic layer is greater than or equal to 1.5 eV. Such an energy level setting can facilitate the rapid improvement of the charge separation ability of the charge generation structure, thereby further improving the carrier transport ability.

[0033] Optionally, a third film layer is further included between the first organic layer and the second organic layer. The LUMO energy level of the third film layer is greater than that of the first organic layer; the HOMO energy level of the third film layer is less than or equal to the HOMO energy level of the first organic layer and greater than or equal to the HOMO energy level of the second organic layer; the difference between the LUMO energy level of the third film layer and the LUMO energy level of the first organic layer is greater than or equal to 0.5 eV.

[0034] Optionally, the third film layer is MoO 3 、V 2 O 5 、WO 3 、ReO 3 、 at least one of NPB.

[0035] Optionally, the thickness range of the third film layer 8 is 1-10 nm.

[0036] Example 1

[0037] This example provides a charge generation structure 1, as Figure 1 shown, a first organic layer 11 and a second organic layer 12.

[0038] As an embodiment of the present invention, in this example, the interfacial roughness of the first organic layer 11 and the second organic layer 12 is 50 nm. The first organic layer 11 is a pentacene material with a thickness of 30 nm, and the second organic layer 12 is copper hexadecafluorophthalocyanine with a thickness of 40 nm. Copper hexadecafluorophthalocyanine is prepared on the electron transport unit of pentacene, so that pentacene can induce copper hexadecafluorophthalocyanine to grow in the same crystal phase, further increasing the grain size, which is not only beneficial to the fusion of grain boundaries, but also can increase the contact area of the charge generation interface and improve the charge generation amount.

[0039] The preparation method of the charge generation structure in this example includes the following steps:

[0040] S1. The first organic layer 11 is formed by vacuum evaporation or spin coating. After preparation, the first organic layer 11 is heated to 80-120 °C and then cooled to room temperature;

[0041] S2. The second organic layer 12 is formed on the cooled first organic layer 11 by vacuum evaporation or spin coating. After preparation, the second organic layer 12 is heated to 80-120 °C and then cooled to room temperature.

[0042] As a changeable embodiment of the present invention, only the first organic layer 11 can be heated and cooled, and the second organic layer 12 can be induced to grow on the crystal phase of the first organic layer 11, so that a high-roughness interface can be formed without heat treatment.

[0043] Optionally, only the second organic layer 12 can be heated and cooled. The first organic layer 11 can be induced to grow on the crystal phase of the second organic layer 12, so that an interface with high roughness can be formed without heat treatment.

[0044] Preferably, the difference in interface roughness between the first organic layer and / or the second organic layer before heating and after cooling is greater than or equal to 10 nm.

[0045] This embodiment also provides a light-emitting device, as Figure 2 shown, including a substrate 2, a first electrode layer 3, a first light-emitting unit 4, a charge generation structure 1, a second light-emitting unit 5, a second electrode layer 6, and a packaging layer 7 which are stacked. The specific device structure is:

[0046] ITO(150 nm) / NPB(40 nm) / ADN:8% DNCA(30 nm) / pentacene(30 nm) / F16-CuPc(40 nm) / NPB(10 nm) / ADN:8% DNCA(30 n) / NABPy(30 nm) / LiF(0.8 nm) / Al(150 nm).

[0047] Among them, the first electrode layer 3 is ITO (indium tin oxide), the first light-emitting unit 4 is NPB(40 nm) / ADN:DNCA(30 nm), the second light-emitting unit 5 is NPB(10 nm) / ADN:DNCA(30 n) / NABPy(30 nm) / LiF(0.8 nm), and the second electrode layer 6 is Al (aluminum).

[0048] Among them, the hole transport layer is: NPB (N,N'-bis(naphthalen-1-yl)N,N'-bis(phenyl)benzidine);

[0049] The light-emitting layer is: ADN(9,10-di(2-naphthyl)anthracene) doped with 8% DNCA (N6,N6,N12,N12-tetrap-tolylchrysene-6,12-diamine);

[0050] The electron transport layer is: NABPy(5,5',5''-(2-(naphthalen-2-yl)anthracene-9,10-diyl)bis(2-phenylpyridine));

[0051] The electron injection layer is LiF (lithium fluoride).

[0052] In this light-emitting device, the first organic layer of pentacene and the second organic layer of F16-CuPc are heated to 100 °C and then cooled to room temperature. After testing with a surface roughness detector, the difference in the interfacial roughness of the first and second organic layers before heating and after cooling is 50 nm.

[0053] As a transformable embodiment of the present invention, the structure of the organic electroluminescent device is not limited to this. As long as the charge generation structure described in the present invention is applied, the object of the present invention can be achieved, which belongs to the protection scope of the present invention.

[0054] The preparation method of the organic electroluminescent device is the same as the prior art except for the charge generation structure.

[0055] Example 2

[0056] This example provides a charge generation structure, as Figure 3 shown. Its structure and preparation method are the same as those in Example 1, except that: a third film layer 8 is further included between the first organic layer 11 and the second organic layer 12. The material of the third film layer 8 is MoO 3 , and the thickness is 3 nm.

[0057] The LUMO energy level of the third film layer 8 is greater than the LUMO energy level of the first organic layer 11. The HOMO energy level of the third film layer is less than or equal to the HOMO energy level of the first organic layer and greater than or equal to the HOMO energy level of the second organic layer. The difference between the LUMO energy level of the third film layer 8 and the LUMO energy level of the first organic layer 11 is greater than or equal to 0.5 eV. The energy level setting of the third film layer 8 as an intermediate layer structure is required to separate electrons and holes, facilitating the rapid transmission of electrons and holes.

[0058] The preparation method of the charge generation structure in this example includes the following steps:

[0059] S1. The first organic layer 11 is formed by vacuum evaporation or spin coating. After preparation, the first organic layer 11 is heated to 80 - 120 °C and then cooled to room temperature;

[0060] S2. The third film layer 8 is formed on the cooled first organic layer 11 by vacuum evaporation or spin coating, and then the second organic layer 12 is formed on the third film layer 8 by vacuum evaporation or spin coating. After preparation, the second organic layer 12 is heated to 80 - 120 °C and then cooled to room temperature.

[0061] Preferably, the glass transition temperature of the third film layer 8 is greater than 120 °C to prevent the heating of the second organic layer 12 from affecting the third film layer 8 and further affecting the charge separation ability of the third film layer 8.

[0062] As a transformable embodiment of the present invention, only the first organic layer 11 can be heated and cooled, and the second organic layer 12 can be induced to grow on the crystal phase of the first organic layer 11, so that an interface with high roughness can be formed without heat treatment.

[0063] Optionally, only the second organic layer 12 can be heated and cooled, and the first organic layer 11 can be induced to grow on the crystal phase of the second organic layer 12, so that an interface with high roughness can be formed without heat treatment. This embodiment also provides an organic electroluminescent device, as Figure 2 shown. Its structure and preparation method are the same as those in Embodiment 1, except that the charge generation structure is the structure described in this embodiment.

[0064] Comparative Example 1

[0065] This comparative example provides a charge generation structure, whose structure is the same as that in Embodiment 1, except that the first organic layer 11 and the second organic layer 12 are not crystallized, and the interface roughness is less than 10 nm.

[0066] Comparative Example 2

[0067] This comparative example provides a charge generation structure, whose structure is the same as that in Embodiment 1, except that the first organic layer 11 is an electron transport layer NABPy with a thickness of 30 nm.

[0068] Perform performance tests on the organic electroluminescent devices provided in the above embodiments and comparative examples, and the test results are shown in the following table:

[0069]

[0070] It can be seen from the above data that under the same brightness condition, the luminous efficiency of the light-emitting device provided by the embodiment of the present invention is higher than that of the device provided in the comparative example, and the voltage is lower than that of the device provided in the comparative example. Therefore, a charge generation structure described in the present invention can effectively improve the efficiency of the device and reduce the voltage, thereby improving the service life of the device.

[0071] Obviously, the above embodiments are merely examples given for clear illustration and are not limitations on the implementation manners. For those of ordinary skill in the art, other different forms of changes or alterations can be made based on the above description. It is not necessary and impossible to list all the implementation manners here. And the obvious changes or alterations derived therefrom are still within the protection scope of the present invention.

Claims

1. A charge generation structure, characterized in that, it includes a first organic layer and a second organic layer. The first organic layer is an induced crystallization material with electron transport characteristics, and the second organic layer is a crystallization material with hole transport characteristics. The interfacial roughness between the first organic layer and the second organic layer is 10 nm to 100 nm; the first organic layer uses pentacene and its derivative materials, and the second organic layer uses copper phthalocyanine fluoride materials. The first organic layer induces the second organic layer to grow in the same crystal phase.

2. The charge generation structure according to claim 1, characterized in that, the thickness of the first organic layer is 1 nm to 100 nm, and the thickness of the second organic layer is 1 nm to 100 nm.

3. The charge generation structure according to claim 1, characterized in that, the LUMO energy level of the first organic layer is greater than the LUMO energy level of the second organic layer, and the HOMO energy level of the second organic layer is less than the HOMO energy level of the first organic layer; the difference between the LUMO energy level of the first organic layer and the LUMO energy level of the second organic layer is ≥ 1.5 eV, and the difference between the HOMO energy level of the first organic layer and the HOMO energy level of the second organic layer is ≥ 1.5 eV.

4. A preparation method of the charge generation structure according to any one of claims 1-3, characterized in that, the first organic layer is formed by vacuum evaporation or spin coating. After preparation, the first organic layer is heated to 80 - 120 °C and then cooled to room temperature; the second organic layer is formed by vacuum evaporation or spin coating. After preparation, the second organic layer is heated to 80 - 120 °C and then cooled to room temperature.

5. The preparation method of the charge generation structure according to claim 4, characterized in that, the difference in interfacial roughness of the first organic layer and / or the second organic layer before heating and after cooling is greater than or equal to 10 nm.

6. A light-emitting device, characterized in that, it includes at least two stacked light-emitting units, and the charge generation structure according to any one of claims 1-3 disposed between adjacent light-emitting units.

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