Quantum dot light emitting device and display device

Abstract

The application discloses a quantum dot light-emitting device and a display device. The quantum dot light-emitting device comprises a cathode, an anode and a light-emitting layer arranged between the cathode and the anode. The light-emitting layer comprises a plurality of quantum dot layers arranged in a stack. The plurality of quantum dot layers comprise a first quantum dot layer and a second quantum dot layer arranged adjacently. The diameter of the quantum dots in the first quantum dot layer is different from the diameter of the quantum dots in the second quantum dot layer. The above scheme can reduce the probability of leakage of the quantum dot light-emitting device and improve the light-emitting efficiency.

Description

Technical Field

[0001] This invention relates to the field of display technology, and in particular to a quantum dot light-emitting device and display apparatus. Background Technology

[0002] QLED (Quantum Dot Light Emitting Diode) is an active-matrix display technology based on the electroluminescence principle of quantum dots. It features ultra-thinness, high color gamut, flexibility, and high contrast, delivering an unparalleled picture quality experience. Undoubtedly, it is the most eye-catching technology in the current quantum dot field and is often referred to as the next generation of display technology. The working principle of QLED is that, driven by an applied voltage, holes are injected from the anode and electrons from the cathode, and the two recombine to emit light in the quantum dot layer.

[0003] The luminous efficiency and stability of existing QLEDs still need to be improved. Summary of the Invention

[0004] The main technical problem solved by this invention is to provide a quantum dot light-emitting device and display device that reduces the probability of leakage and improves luminous efficiency.

[0005] To solve the above-mentioned technical problems, one technical solution adopted by the present invention is to provide a quantum dot light-emitting device, including a cathode, an anode, and a light-emitting layer disposed between the cathode and the anode; the light-emitting layer includes multiple quantum dot layers stacked together, the multiple quantum dot layers including a first quantum dot layer and a second quantum dot layer disposed adjacent to each other, wherein the diameter of the quantum dots in the first quantum dot layer is different from the diameter of the quantum dots in the second quantum dot layer.

[0006] To solve the above-mentioned technical problems, another technical solution adopted by the present invention is to provide a display device, including the quantum dot light-emitting device in any embodiment.

[0007] The beneficial effects of this invention are as follows: Unlike the prior art, the light-emitting layer of the quantum dot light-emitting device of this invention includes adjacent first quantum dot layers and second quantum dot layers. Since the quantum dots in the first and second quantum dot layers have different diameters and are arranged adjacent to each other, there is a larger gap between the larger diameter quantum dots, allowing the smaller diameter quantum dots to fill the gap. The quantum dots in the adjacent quantum dot layers achieve self-filling, forming a relatively dense light-emitting layer. This reduces the probability that holes on the anode side of the light-emitting layer will directly transfer to the other side of the light-emitting layer through the gap, thereby reducing the leakage current problem of the quantum dot light-emitting device and improving the stability of the light-emitting device. On the other hand, it reduces the probability that the material on the cathode side of the light-emitting layer will fill the light-emitting layer, avoiding the quantum dots being blocked from emission, thereby improving the luminous efficiency. Attached Figure Description

[0008] Figure 1 This is a schematic diagram of one embodiment of the quantum dot light-emitting device of the present invention;

[0009] Figure 2 This is a top view of one embodiment of the light-emitting layer of the present invention;

[0010] Figure 3 This is a schematic diagram of another embodiment of the quantum dot light-emitting device of the present invention;

[0011] Figure 4 This is a schematic diagram of another embodiment of the quantum dot light-emitting device of the present invention. Detailed Implementation

[0012] To make the objectives, technical solutions, and effects of this invention clearer and more explicit, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. Obviously, the described embodiments are only a part of the embodiments of this invention, and not all of them. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this invention.

[0013] Existing quantum dot light-emitting devices typically include a cathode, an anode, and a quantum dot light-emitting layer disposed between the cathode and the anode. The quantum dot light-emitting layer comprises quantum dot (QD) material, which emits light of relatively pure colors when excited. The inventors discovered that due to the particle nature of quantum dots, it is difficult to form a dense quantum dot light-emitting layer. Therefore, material on the cathode side of the light-emitting layer tends to fill the gaps between the quantum dots. This suppresses quantum dot emission, reducing luminous efficiency. Furthermore, holes on the anode side of the light-emitting layer can directly transfer through the gaps, leading to leakage current.

[0014] In view of this, the present invention provides a quantum dot light-emitting device to overcome the above-mentioned defects. See also... Figure 1 , Figure 1 This is a schematic diagram of one embodiment of the quantum dot light-emitting device of the present invention. The quantum dot light-emitting device 10 includes a cathode 11, an anode 16, and a light-emitting layer 13 disposed between the cathode 11 and the anode 16; the light-emitting layer 13 includes multiple quantum dot layers stacked together, the multiple quantum dot layers including a first quantum dot layer 131 and a second quantum dot layer 132 disposed adjacently, wherein the diameter of the quantum dots in the first quantum dot layer 131 is different from the diameter of the quantum dots in the second quantum dot layer 132.

[0015] The light-emitting layer 13 of the quantum dot light-emitting device 10 of the present invention includes an adjacent first quantum dot layer 131 and a second quantum dot layer 132. Since the first quantum dot layer 131 and the second quantum dot layer 132 are arranged adjacently and the quantum dots in them have different diameters, there is a larger gap between the quantum dots with larger diameters, which allows the quantum dots with smaller diameters to fill the gaps. The quantum dots in the adjacent quantum dot layers achieve self-filling, forming a relatively dense light-emitting layer 13. This reduces the probability that holes will pass through the gaps in the light-emitting layer 13 from the side of the light-emitting layer 13 facing the anode 16 and directly transfer to the side of the light-emitting layer 13 facing the cathode 11. This reduces the leakage current problem of the quantum dot light-emitting device 10 and improves the stability of the light-emitting device. On the other hand, it reduces the probability that the material on the side of the light-emitting layer 13 near the cathode 11 will fill the light-emitting layer 13, avoiding the quantum dots being blocked from emission, thereby ensuring the luminous efficiency.

[0016] The number of quantum dot layers in the light-emitting layer 13 is at least two. In some embodiments, the number of quantum dot layers is two, namely a first quantum dot layer 131 and a second quantum dot layer 132 stacked together.

[0017] Optionally, in such Figure 1 In the embodiment shown, in the direction from cathode 11 to anode 16 ( Figure 1 In the Z-direction, the first quantum dot layer 131 and the second quantum dot layer 132 are stacked sequentially, and the diameter of the quantum dots in the first quantum dot layer 131 is smaller than the diameter of the quantum dots in the second quantum dot layer 132.

[0018] See Figure 2 , Figure 2 This is a top view of one embodiment of the light-emitting layer of the present invention. The figure schematically shows the internal structure of the first quantum dot layer 131 and the second quantum dot layer 132. The quantum dots in the first quantum dot layer 131 are defined as first quantum dots 1311, and the quantum dots in the second quantum dot layer 132 are defined as second quantum dots 1321. As can be seen from the figure, the diameter of the first quantum dot 1311 is smaller than the diameter of the second quantum dot 1321. Because the diameter of the second quantum dot 1321 is larger, there are larger gaps between the multiple second quantum dots 1321. However, because the diameter of the first quantum dot 1311 is smaller, the first quantum dots 1311 can fill the gaps between the second quantum dots 1321, thereby reducing the gaps in the light-emitting layer and improving the density of the light-emitting layer. The material on the cathode side has difficulty passing through the gaps, thereby reducing the probability of the first quantum dots 1311 and the second quantum dots 1321 being blocked from emission, improving the luminous efficiency, and reducing the leakage current caused by the contact between the anode-side holes and the cathode-side material.

[0019] It should be noted that the quantum dot light-emitting device 10 in this embodiment can be upright or inverted. When the quantum dot light-emitting device 10 is upright, the anode 16 is disposed on the side close to the substrate (not shown). Specifically, the cathode 11 is located at the top, and an electron transport layer (ETL) 12 is disposed between the cathode 11 and the first quantum dot layer 131. Specifically, the electron transport layer 12 is usually made of materials such as zinc oxide magnesium MgZnO or zinc oxide ZnO. A hole transport layer (HTL) 14 and a hole injection layer (HIL) 15 are disposed between the second quantum dot layer 132 and the anode 16. The hole transport layer 14 is disposed on the side of the hole injection layer 15 away from the anode 16. Because the quantum dot light-emitting device 10 has an upright structure, with the smaller-diameter first quantum dot 1311 positioned above the second quantum dot 1321, the first quantum dot 1311 can more easily fill the gap between the second quantum dot 1321 under the influence of gravity. Furthermore, since the first quantum dot 1311 has a smaller diameter, the first quantum dot layer 131 is more compact than the second quantum dot layer 132. This means the denser first quantum dot layer 131 is closer to the electron transport layer 12. This prevents smaller-diameter zinc oxide (MgZnO) or zinc oxide (ZnO) particles from passing through the first and second quantum dot layers 131 and 132, thus avoiding direct contact between the electron transport layer 12 material and holes and reducing the probability of leakage current. It also reduces the probability of the electron transport layer 12 material filling the gap between the first and second quantum dot layers 131 and 132, ensuring the normal emission of both the first and second quantum dots 1311 and 1321, thereby guaranteeing luminous efficiency. In other embodiments, the diameter of the first quantum dot 1311 may also be larger than the diameter of the second quantum dot 1321.

[0020] See Figure 3 , Figure 3 This is a schematic diagram of another embodiment of the quantum dot light-emitting device of the present invention. Figure 2Similar to the illustrated embodiment, the diameter of the first quantum dot 1311 is smaller than the diameter of the second quantum dot 1321. In this embodiment, the quantum dot light-emitting device 10 has an inverted structure, with the cathode 11 disposed on the side near the substrate (not shown). Specifically, the anode 16 is located at the top, an electron transport layer 12 is provided between the cathode 11 and the second quantum dot layer 132, and a hole transport layer 14 and a hole injection layer 15 are provided between the first quantum dot layer 131 and the anode 16. The hole transport layer 14 is disposed on the side of the hole injection layer 15 facing away from the anode 16. Because the smaller-diameter first quantum dot 1311 is located above the second quantum dot 1321, under the influence of gravity, the first quantum dot 1311 is more likely to automatically fill the gaps between the second quantum dots 1321, thereby improving the density of the light-emitting layer 13. In other embodiments, the diameter of the first quantum dot 1311 can be larger than the diameter of the second quantum dot 1321, thereby making the second quantum dot layer 132 near the electron transport layer 12 more dense.

[0021] Optionally, the emission peak position of the first quantum dot 1311 is the same as that of the second quantum dot 1321. This arrangement ensures that the emitted light from the first quantum dot layer 131 and the second quantum dot layer 132 is of the same color, resulting in higher color purity for the quantum dot light-emitting device 10. For example, the emitted light from the first quantum dot layer 131 and the second quantum dot layer 132 can be red, green, or blue, etc.

[0022] Optionally, the first quantum dot 1311 includes a first core and a first shell covering the first core, and the second quantum dot 1321 includes a second core and a second shell covering the second core; wherein the diameter of the first core is equal to the diameter of the second core, and the thickness of the first shell is less than the thickness of the second shell.

[0023] Spherical quantum dots often employ a core-shell structure. When excited by an electric field, the core emits colored light, the color of which is influenced by the core size. When the core is small (e.g., 5-6 nm in diameter), the quantum dot absorbs long wavelengths and emits blue light; when the core is large (e.g., 9-10 nm), it absorbs short wavelengths and emits red light. Cores of the same diameter emit light of the same color, ensuring the purity of the light color emitted by the same quantum dot light-emitting device 10. Due to the high electronic activity of the core, a shell covering the core surface is used for passivation, suppressing electron movement within the quantum dot and preventing them from detaching randomly. This core-shell structure enhances the quantum dot's resistance to photo-oxidation and improves its chemical and thermodynamic stability. Since the first and second cores have the same diameter, different diameters for the first quantum dot 1311 and the second quantum dot 1321 can be achieved by changing the thickness of either the first quantum dot 1311 or the second quantum dot 1321. For example, the diameters of the first and second cores are both 5 nm, while the diameter of the first quantum dot 1311 is 6.5 nm and the diameter of the second quantum dot 1321 is 20 nm. Therefore, the thickness of the first shell is 0.75 nm and the thickness of the second shell is 7.5 nm.

[0024] Specifically, the materials of the first and second cores include at least one selected from cadmium selenide (CdSe), zinc cadmium selenide (CdZnSe), zinc cadmium sulfide (CdZnS), zinc selenide (ZnSe), and indium phosphide (InP). The materials of the first and second cores can be the same or different, both emitting light of the same color. The materials of the first and second shells can be cadmium sulfide (CdS), zinc sulfide (ZnS), etc. The materials of the first and second cores can be the same or different; this invention does not impose limitations. The first and second shells can contain only one material or can include multiple materials. For example, the first shell can be made of cadmium sulfide (CdS), and the second shell can have an inner layer of cadmium sulfide (CdS) and an outer layer of zinc sulfide (ZnS).

[0025] The inventors discovered that, because the second shell thickness of the second quantum dot 1321 in this embodiment is thicker than that of the first quantum dot 1311, the second quantum dot 1321 has higher stability. At the same time, the minimum distance between the two quantum dots is the sum of the shell thicknesses of the two quantum dots. Furthermore, due to the thicker second shell, the distance between the two second quantum dots 1321 and between the first quantum dot 1311 and the second quantum dot 1321 is increased, thereby reducing the probability of Foster resonance energy transfer (FRET) between quantum dots, thus ensuring the stability of the quantum dots and improving the lifetime of the quantum dot device.

[0026] Optionally, the thickness of the first quantum dot layer 1311 is less than the thickness of the second quantum dot layer 1321. Since the number of quantum dots contained in the thinner quantum dot layer is correspondingly smaller, the proportion of the first quantum dot 131 in all quantum dots is reduced, further reducing the probability of Foster energy transfer between quantum dots, thereby further ensuring the stability and lifetime of the device.

[0027] In other embodiments, to further improve the density of the light-emitting layer 13, the number of quantum dot layers can be set to three or more.

[0028] Optionally, see Figure 4 , Figure 4 This is a schematic diagram of another embodiment of the quantum dot light-emitting device of the present invention. There are three quantum dot layers. In the direction from the cathode 11 to the anode 16 (Z direction in the figure), the light-emitting layer 13 includes a first quantum dot layer 131, a second quantum dot layer 132, and a third quantum dot layer 133 stacked sequentially. The diameter of the quantum dots in the multiple quantum dot layers increases along the Z direction; that is, the diameter of the quantum dots in the first quantum dot layer 131 is smaller than the diameter of the quantum dots in the second quantum dot layer 132, and the diameter of the quantum dots in the second quantum dot layer 132 is smaller than the diameter of the quantum dots in the third quantum dot layer 133. The quantum dots in the first quantum dot layer 131 are defined as the first quantum dot (…). Figure 4 (Not shown), the quantum dots in the second quantum dot layer 132 are defined as second quantum dots ( Figure 4 (Not shown), the quantum dots in the third quantum dot layer 133 are defined as third quantum dots ( Figure 4 (Not shown). Optionally, the diameter of the first quantum dot is smaller than the diameter of the second quantum dot, and the diameter of the second quantum dot is smaller than the diameter of the third quantum dot.

[0029] Because the third quantum dot has the largest diameter, there are large gaps between multiple third quantum dots. Since the diameter of the second quantum dot is smaller than that of the third quantum dot, the second quantum dot can fill the gaps between the third quantum dots. Since the diameter of the first quantum dot is smaller than that of the second quantum dot, the first quantum dot can fill the gaps between the second quantum dots. The quantum dot layers with large gaps in the light-emitting layer 13 are all filled by the quantum dots of the adjacent quantum dot layers, thereby further improving the compactness of the light-emitting layer 13. The material on the cathode side has difficulty passing through the gaps in the light-emitting layer 13, thus reducing the probability of quantum dots being blocked from emission and improving the luminous efficiency. On the other hand, it also reduces the leakage current caused by the contact between the hole on the anode side and the material on the cathode side.

[0030] In another embodiment, the diameter of the second quantum dot can be set to be the smallest, while the diameters of the first and third quantum dots are larger, and their diameters can be the same or different. This arrangement allows the second quantum dot to fill the gaps formed between multiple first and third quantum dots, thereby improving the density of the light-emitting layer. In other embodiments, the diameters of the quantum dots in any two adjacent quantum dot layers can be set to be different to achieve self-filling of the quantum dots in the light-emitting layer 13.

[0031] The number of quantum dot layers can be increased, for example, to four or five layers. Optionally, the number of quantum dot layers can be less than or equal to five to avoid the quantum dot light-emitting device 10 being difficult to microcavity tune due to an excessively thick light-emitting layer. Optionally, to ensure the purity of the emitted rays, the emission peak positions of the quantum dots in the multi-layer quantum dot layer are all the same. Specifically, the quantum dots in the multi-layer quantum dot layer can all be configured as core-shell structures, and the core diameter of all quantum dots can be the same to ensure that the emission peak positions of the quantum dots are all the same.

[0032] The present invention also provides a display device, including the quantum dot light-emitting device in any of the above embodiments. This display device can be a mobile phone, tablet computer, wearable smart device, etc.

[0033] The above are merely embodiments of the present invention and do not limit the patent scope of the present invention. Any equivalent structural or procedural transformations made based on the content of the present invention's specification and drawings, or direct or indirect applications in other related technical fields, are similarly included within the patent protection scope of the present invention.

Claims

1. A quantum dot light-emitting device, characterized in that, It includes a cathode, an anode, and a light-emitting layer disposed between the cathode and the anode; The light-emitting layer includes multiple quantum dot layers stacked together, each quantum dot layer including a first quantum dot layer and a second quantum dot layer arranged adjacent to each other, wherein the diameter of the quantum dots in the first quantum dot layer is different from the diameter of the quantum dots in the second quantum dot layer; In the direction from the cathode to the anode, the first quantum dot layer and the second quantum dot layer are stacked sequentially, and the diameter of the quantum dots in the first quantum dot layer is smaller than the diameter of the quantum dots in the second quantum dot layer, with the quantum dots in the first quantum dot layer filling the gaps between the quantum dots in the second quantum dot layer; In this design, the quantum dots in the first quantum dot layer are defined as first quantum dots, and the quantum dots in the second quantum dot layer are defined as second quantum dots. The first quantum dot includes a first core and a first shell covering the first core, and the second quantum dot includes a second core and a second shell covering the second core. The diameter of the first core is equal to the diameter of the second core, and the thickness of the first shell is less than the thickness of the second shell.

2. The quantum dot light-emitting device according to claim 1, characterized in that, The number of quantum dot layers is greater than or equal to three, and the diameter of the quantum dots in the plurality of quantum dot layers increases in the direction from the cathode to the anode.

3. The quantum dot light-emitting device according to claim 2, characterized in that, The number of quantum dot layers is less than or equal to five.

4. The quantum dot light-emitting device according to claim 1, characterized in that, The emission peak position of the quantum dots in the first quantum dot layer is the same as that of the quantum dots in the second quantum dot layer.

5. The quantum dot light-emitting device according to claim 4, characterized in that, The emission peak positions of the quantum dots in the multi-layer quantum dot layer are all the same.

6. The quantum dot light-emitting device according to claim 1, characterized in that, The material of the first core / second core includes at least one of cadmium selenide (CdSe), zinc cadmium selenide (CdZnSe), zinc cadmium sulfur (CdZnS), zinc selenide (ZnSe), and indium phosphide (InP).

7. The quantum dot light-emitting device according to claim 6, characterized in that, The first kernel and the second kernel are made of the same material.

8. The quantum dot light-emitting device according to claim 6, characterized in that, The first shell layer and the second shell layer are made of the same material.

9. The quantum dot light-emitting device according to claim 1, characterized in that, The thickness of the first quantum dot layer is less than the thickness of the second quantum dot layer.

10. The quantum dot light-emitting device according to claim 1, characterized in that, An electron transport layer is provided between the cathode and the light-emitting layer, and a hole transport layer and a hole injection layer are provided between the light-emitting layer and the anode. The hole transport layer is disposed on the side of the hole injection layer opposite to the anode.

11. The quantum dot light-emitting device according to claim 1, characterized in that, Multiple first quantum dots form a virtual polygon, wherein the orthographic projection of the first quantum dot at the vertex of the virtual polygon onto the anode at least partially coincides with the orthographic projection of the gap between two adjacent second quantum dots onto the anode, and the orthographic projection of the first quantum dot at the center of the virtual polygon onto the anode lies within the orthographic projection of the second quantum dot onto the anode.

12. A display device, characterized in that, Including the quantum dot light-emitting device as described in any one of claims 1-11.

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