Quantum dot light-emitting device and display device

Abstract

The invention 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 multiple quantum dot layers which are arranged in a stacked mode, the multiple quantum dot layers comprise a first quantum dot layer and a second quantum dot layer which are arranged adjacently, and the diameter of quantum dots in the first quantum dot layer is different from that of quantum dots in the second quantum dot layer. Through the scheme, the probability of electric leakage of the quantum dot light-emitting device can be reduced, and the light-emitting efficiency is improved.

Description

Technical Field

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

[0002] QLED (Quantum Dot Light Emitting Diode) is an active light-emitting display technology based on the principle of quantum dot electroluminescence. It has the characteristics of ultra-thinness, high color gamut, flexibility, high contrast, etc., which can bring unparalleled picture quality experience. It is undoubtedly the most eye-catching technical direction in the current quantum dot camp, and is also known as the next generation of display technology. The working principle of QLED is that under the drive of an external voltage, holes are injected from the anode and electrons are injected from the cathode, and the two form excitons in the quantum dot layer to recombine and emit light.

[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 the present invention is to provide a quantum dot light-emitting device and a display device, which reduce the probability of leakage and improve the light-emitting efficiency.

[0005] In order to solve the above technical problems, a 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 arranged between the cathode and the anode; the light-emitting layer includes a plurality of quantum dot layers stacked together, and the plurality of quantum dot layers include a first quantum dot layer and a second quantum dot layer 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] In order to solve the above technical problem, 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 the present invention are as follows: different from the prior art, the light-emitting layer in the quantum dot light-emitting device of the present invention includes an adjacent first quantum dot layer and a second quantum dot layer. Since the diameters of the quantum dots in the first quantum dot layer and the second quantum dot layer are different and the two are arranged adjacent to each other, there is a larger gap between the quantum dots with a larger diameter, so that the quantum dots with a smaller diameter can be filled into the above gap, and the quantum dots in the adjacent quantum dot layers achieve self-filling to form a relatively dense light-emitting layer, thereby reducing the probability of holes on the side of the light-emitting layer facing the anode passing through the gap in the light-emitting layer and directly transferring to the other side of the light-emitting layer, thereby reducing the problem of leakage current of the quantum dot light-emitting device and improving the stability of the light-emitting device; on the other hand, it reduces the probability of materials on the side of the light-emitting layer close to the cathode being filled into the light-emitting layer, avoiding the quantum dots from being blocked from emitting, thereby improving the light-emitting efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

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

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

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

[0011] Figure 4 It is a schematic structural diagram of another embodiment of the quantum dot light-emitting device of the present invention. DETAILED DESCRIPTION

[0012] In order to make the purpose, technical scheme and effect of the present invention clearer and more specific, the present invention is further described in detail with reference to the accompanying drawings and examples. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0013] Existing quantum dot light-emitting devices usually include a cathode, an anode, and a quantum dot light-emitting layer disposed between the cathode and the anode, wherein the quantum dot light-emitting layer includes quantum dot (QD) materials, and the quantum dots can emit light of relatively pure colors after being excited. The inventors found that due to the particle nature of quantum dots, it is difficult to form a dense quantum dot light-emitting layer, so the material located on the side of the light-emitting layer close to the cathode is easy to fill in the gaps between the quantum dots, which will inhibit the emission of quantum dots and reduce the luminous efficiency on the one hand, and on the other hand, the holes located on the side of the light-emitting layer close to the anode can be directly transferred through the gap, thereby causing leakage current.

[0014] In view of this, the present invention provides a quantum dot light emitting device to overcome the above-mentioned defects. Figure 1 , Figure 1 1 is a schematic diagram of the structure of an embodiment of a quantum dot light-emitting device of the present invention. The quantum dot light-emitting device 10 comprises 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 comprises a plurality of stacked quantum dot layers, the plurality of quantum dot layers comprises 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 in 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 adjacently arranged and the diameters of the quantum dots therein are different, there is a larger gap between the quantum dots with a larger diameter, so that the quantum dots with a smaller diameter can be filled into the above gap, and the quantum dots in the adjacent quantum dot layers achieve self-filling to form a relatively dense light-emitting layer 13, thereby reducing the probability of holes directly transferring from the side of the light-emitting layer 13 facing the anode 16 through the gap of the light-emitting layer 13 to the side of the light-emitting layer 13 facing the cathode 11, thereby reducing the problem of leakage current of the quantum dot light-emitting device 10 and improving the stability of the light-emitting device; on the other hand, it reduces the probability of the material on the side of the light-emitting layer 13 close to the cathode 11 being filled into the light-emitting layer 13, thereby avoiding the quantum dots from being blocked from emitting, thereby ensuring the light-emitting 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 which are stacked.

[0017] Optionally, in 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 in sequence, 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 also Figure 2 , Figure 2 It is a top view of an 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. It can be seen from the figure that the diameter of the first quantum dot 1311 is smaller than the diameter of the second quantum dot 1321. Due to the large diameter of the second quantum dot 1321, there is a large gap between the plurality of second quantum dots 1321, and due to the small diameter of the first quantum dot 1311, the first quantum dot 1311 can be filled into the gap between the second quantum dots 1321, thereby reducing the gap in the light-emitting layer and improving the compactness of the light-emitting layer. It is difficult for the material on the cathode side to pass through the gap, thereby reducing the probability of the first quantum dot 1311 and the second quantum dot 1321 being blocked from emitting, improving the luminous efficiency, and reducing the leakage current caused by the contact between the anode side holes and the cathode side materials on the other hand.

[0019] It should be noted that the quantum dot light-emitting device 10 of this embodiment can be upright or inverted. When the quantum dot light-emitting device 10 is an upright structure, the anode 16 is arranged on a side close to the substrate (not shown), specifically, the cathode 11 is located at the top, and an electron transport layer (ETL) 12 is arranged 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, and a hole transport layer (HTL) 14 and a hole injection layer (HIL) 15 are arranged between the second quantum dot layer 132 and the anode 16, and the hole transport layer 14 is arranged on the side of the hole injection layer 15 away from the anode 16. Since the quantum dot light-emitting device 10 is an upright structure, that is, the first quantum dot 1311 with a smaller diameter is located above the second quantum dot 1321, so that under the action of gravity, the first quantum dot 1311 is more likely to automatically fill into the gap between the second quantum dot 1321; and since the diameter of the first quantum dot 1311 is smaller, that is, the first quantum dot layer 131 is denser than the second quantum dot layer 132, that is, the denser first quantum dot layer 131 is closer to the electron transport layer 12, so that on the one hand, the zinc oxide magnesium MgZnO or zinc oxide ZnO particles with smaller diameters are avoided from passing through the first quantum dot layer 131 and the second quantum dot layer 132, thereby avoiding the direct contact between the electron transport layer 12 material and the holes, reducing the probability of leakage current; on the other hand, the probability of the electron transport layer 12 material filling into the gap between the first quantum dot layer 131 or the second quantum dot layer 132 is reduced, thereby ensuring the normal emission of the first quantum dot 1311 and the second quantum dot 1321, thereby ensuring the luminous efficiency. In other embodiments, the diameter of the first quantum dot 1311 may also be greater than the diameter of the second quantum dot 1321 .

[0020] See also Figure 3 , Figure 3 Schematic diagram of another embodiment of the quantum dot light emitting device of the present invention. Figure 2The same as the embodiment shown is that 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 is an inverted structure, the cathode 11 is arranged on the side close to 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, a hole transport layer 14 and a hole injection layer 15 are provided between the first quantum dot layer 131 and the anode 16, and the hole transport layer 14 is provided on the side of the hole injection layer 15 away from the anode 16. Since the first quantum dot 1311 with a smaller diameter is located above the second quantum dot 1321, under the action of gravity, the first quantum dot 1311 is more likely to automatically fill the gap between the second quantum dot 1321, thereby improving the compactness of the light-emitting layer 13. In other embodiments, the diameter of the first quantum dot 1311 can be greater than the diameter of the second quantum dot 1321, so that the second quantum dot layer 132 close to the electron transport layer 12 is more compact.

[0021] Optionally, the luminescence peak position of the first quantum dot 1311 is the same as the luminescence peak position of the second quantum dot 1321. This arrangement makes the light emitted by the first quantum dot layer 131 and the second quantum dot layer 132 have the same color, so that the color purity of the quantum dot light-emitting device 10 is higher. For example, the color of the light emitted by the first quantum dot layer 131 and the second quantum dot layer 132 can be red, green, 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 mostly adopt a core-shell structure, in which, when excited by an electric field, the core will emit colored light, and the color of the light is affected by the size of the core. When the size of the core is small (for example, a diameter of 5-6nm), the quantum dot will absorb long waves and emit blue light. When the size of the core is large (for example, 9-10nm), the quantum dot will absorb short waves and emit red light. The cores with the same diameter emit the same color of light, thereby ensuring the purity of the color of the light emitted by the same quantum dot light-emitting device 10. Due to the high electronic activity of the core, the shell layer coated on the surface of the core is used for passivation, thereby inhibiting the movement of electrons in the quantum dot and preventing them from arbitrarily leaving the quantum dot. The core-shell structure formed can enhance the anti-photooxidation ability of the quantum dot and improve the chemical and thermodynamic stability. Since the diameters of the first core and the second core are the same, if you want to achieve different diameters of the first quantum dot 1311 and the second quantum dot 1321, you can achieve this by changing the thickness of the first quantum dot 1311 or the second quantum dot 1321. For example, the diameters of the first core and the second core 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. It can be concluded that 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 core and the second core include at least one of cadmium selenide CdSe, cadmium zinc selenide CdZnSe, cadmium zinc sulfide CdZnS, zinc selenide ZnSe, and indium phosphide InP. The materials of the first core and the second core can be the same or different, and both can emit light of the same color. The materials of the first shell and the second shell can be materials such as cadmium sulfide CdS and zinc sulfide ZnS. The materials of the first core and the second core can be the same or different, and the present invention does not limit this. The first shell and the second shell can have only one material or include multiple materials. For example, the material of the first shell can be cadmium sulfide CdS, and the material of the second shell can be an inner layer of cadmium sulfide CdS and an outer layer of zinc sulfide ZnS.

[0025] The inventors found that since 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, and since the second shell is thicker, 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 Forster resonance energy transfer (FRET) between quantum dots, thereby ensuring the stability of the quantum dots and improving the life 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 quantum dot layer with a smaller thickness contains fewer quantum dots, the proportion of the first quantum dot 131 in all quantum dots is reduced, further reducing the probability of Förster energy transfer between quantum dots, thereby further ensuring the stability and life of the device.

[0027] In other embodiments, in order to further improve the compactness of the light-emitting layer 13, the number of quantum dot layers can be set to be greater than or equal to three layers.

[0028] Optionally, see Figure 4 , Figure 4 It is a schematic diagram of the structure of another embodiment of the quantum dot light-emitting device of the present invention. The number of quantum dot layers is three. 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 in sequence, and 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 dots ( 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] Since the diameter of the third quantum dot is the largest, there are larger gaps between the multiple third quantum dots, and since the diameter of the second quantum dot is smaller than that of the third quantum dot, the second quantum dot can be filled into the gaps between the third quantum dots, and since the diameter of the first quantum dot is smaller than that of the second quantum dot, the first quantum dot can be filled into the gaps between the second quantum dots. The quantum dot layers with larger gaps in the light-emitting layer 13 are all filled with quantum dots of the adjacent quantum dot layers, thereby further improving the density of the light-emitting layer 13, and it is difficult for the material on the cathode side to pass through the gaps in the light-emitting layer 13, thereby reducing the probability of the quantum dots being blocked from emitting and improving the luminescence efficiency on the one hand, and reducing the leakage current caused by the contact between the holes on the anode side and the materials on the cathode side on the other hand.

[0030] In another embodiment, the diameter of the second quantum dot can also be set to be the smallest, and the diameters of the first quantum dot and the third quantum dot can be larger, and the diameters of the two can be the same or different. The above setting allows the second quantum dot to be filled into the gaps formed between the plurality of first quantum dots and the plurality of third quantum dots, thereby improving the density of the light-emitting layer. In other embodiments, the diameters of the quantum dots of any two adjacent quantum dot layers can also 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 more, for example, four or five layers. Optionally, the number of quantum dot layers is less than or equal to five layers to avoid the light-emitting layer being too thick, which makes it difficult for the quantum dot light-emitting device 10 to perform microcavity adjustment. Optionally, in order to ensure the purity of the light emitted by the light-emitting layer, the luminescence peak positions of the quantum dots in the multi-layer quantum dot layers are the same. Specifically, the quantum dots in the multi-layer quantum dot layers can be set to a core-shell structure, and the core diameters of all quantum dots are the same to ensure that the luminescence peak positions of the quantum dots are the same.

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

[0033] The above are only implementation modes of the present invention, and are not intended to limit the patent scope of the present invention. Any equivalent structure or equivalent process transformation made using the contents of the present invention specification and drawings, or directly or indirectly applied in other related technical fields, are also included in the patent protection scope of the present invention.

Claims

1. A quantum dot light-emitting device, characterized in that: comprising a cathode, an anode and a light-emitting layer disposed between the cathode and the anode; The light-emitting layer includes a plurality of quantum dot layers stacked together, wherein the plurality of quantum dot layers include a first quantum dot layer and a second quantum dot layer adjacent to each other, wherein a diameter of quantum dots in the first quantum dot layer is different from a diameter of quantum dots in the second quantum dot layer.

2. The quantum dot light emitting device according to claim 1, characterized in that In the direction from the cathode to the anode, the first quantum dot layer and the second quantum dot layer are stacked in sequence, 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.

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

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

5. The quantum dot light emitting device according to claim 1, characterized in that: The luminescence peak position of the quantum dots in the first quantum dot layer is the same as the luminescence peak position of the quantum dots in the second quantum dot layer; Preferably, the luminescence peak positions of the quantum dots in the multiple quantum dot layers are all the same.

6. The quantum dot light emitting device according to claim 5, characterized in that: 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 layer covering the first core, and the second quantum dot includes a second core and a second shell layer covering the second core; The diameter of the first inner core is equal to the diameter of the second inner core, and the thickness of the first shell layer is less than the thickness of the second shell layer.

7. The quantum dot light emitting device according to claim 6, characterized in that: The material of the first core / the second core includes at least one of cadmium selenide CdSe, cadmium zinc selenide CdZnSe, cadmium zinc sulfur CdZnS, zinc selenide ZnSe, and indium phosphide InP; Preferably, the material of the first core and the material of the second core are the same; Preferably, the material of the first shell layer and the material of the second shell layer are the same.

8. The quantum dot light emitting device according to claim 6, characterized in that: The thickness of the first quantum dot layer is smaller than the thickness of the second quantum dot layer.

9. 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, a hole transport layer and a hole injection layer are provided between the light-emitting layer and the anode, and the hole transport layer is provided on a side of the hole injection layer away from the anode.

10. A display device, characterized in that: A quantum dot light-emitting device comprising the device described in any one of claims 1 to 9.

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