Quantum dot light emitting diode, display substrate and display device

Abstract

The utility model discloses a quantum dot light emitting diode, a display substrate and a display device. The quantum dot light-emitting diode comprises a first electrode, a second electrode, and a quantum dot light-emitting layer, a first electron transport layer and a second electron transport layer which are arranged between the first electrode and the second electrode, wherein the first electron transport layer and the second electron transport layer are sequentially arranged on one side, close to the second electrode, of the quantum dot light-emitting layer; wherein the first electron transport layer and the second electron transport layer are made of inorganic nanoparticles, the conduction band bottom energy level of the first electron transport layer is matched with the conduction band bottom energy level of the quantum dot light-emitting layer, and the conduction band bottom energy level of the second electron transport layer is larger than the work function of the second electrode and smaller than the conduction band bottom energy level of the first electron transport layer; the carrier mobility of the second electron transport layer is greater than that of the first electron transport layer, and the second electron transport layer is configured to adjust the length of the optical microcavity between the first electrode and the second electrode.

Description

Technical Field

[0001] The utility model relates to display technology, and more specifically, to a quantum dot light emitting diode, a display substrate and a display device. Background Art

[0002] Light-emitting diode (LED) displays have attracted widespread attention in the industry due to their advantages, including self-luminescence, high brightness, low operating voltage, low power consumption, long life, impact resistance, and stable performance. Furthermore, because LED displays do not require a separate backlight module, they are lightweight, facilitating thinner and lighter displays, and therefore have promising market prospects.

[0003] Quantum dots (QDs) are a new type of luminescent material with advantages such as high light color purity, high quantum efficiency, tunable light color, and long lifespan. They have become a research hotspot for new LED luminescent materials. Quantum dot light emitting diodes (QLEDs), which use quantum dot materials as the light-emitting layer, have become a major research focus for new display devices. Utility Model Content

[0004] The embodiments of the present invention provide a quantum dot light emitting diode, a display substrate and a display device.

[0005] In a first aspect, an embodiment of the present invention provides a quantum dot light-emitting diode, comprising: a first electrode, a second electrode, and a quantum dot light-emitting layer, a first electron transport layer, and a second electron transport layer arranged between the first electrode and the second electrode, wherein the first electron transport layer and the second electron transport layer are sequentially arranged on the side of the quantum dot light-emitting layer close to the second electrode; wherein the materials of the first electron transport layer and the second electron transport layer include inorganic nanoparticles, the conduction band bottom energy level of the first electron transport layer matches the conduction band bottom energy level of the quantum dot light-emitting layer, the conduction band bottom energy level of the second electron transport layer is greater than the work function of the second electrode and less than the conduction band bottom energy level of the first electron transport layer; the carrier mobility of the second electron transport layer is greater than the carrier mobility of the first electron transport layer, and the second electron transport layer is configured to adjust the length of the optical microcavity between the first electrode and the second electrode.

[0006] In an exemplary embodiment, the material of the second electron transport layer includes N-type doped zinc oxide nanoparticles.

[0007] In an exemplary embodiment, a ratio of an amount of a substance of the doping element to an amount of a substance of zinc in the second electron transport layer is greater than or equal to 0.1% and less than or equal to 15%.

[0008] In an exemplary embodiment, the doping element in the second electron transport layer includes at least one of a trivalent element and a tetravalent element.

[0009] In an exemplary embodiment, the doping element includes one or more of the following: boron, aluminum, gallium, indium, and silicon.

[0010] In an exemplary embodiment, the conduction band bottom energy level of the first electron transport layer matches the conduction band bottom energy level of the quantum dot light-emitting layer, including: the difference between the conduction band bottom energy level of the first electron transport layer and the conduction band bottom energy level of the quantum dot light-emitting layer is less than or equal to 0.5 eV.

[0011] In an exemplary embodiment, the sum of the thicknesses of the first electron transport layer and the second electron transport layer is greater than or equal to 70 nm and less than or equal to 190 nm; the thickness of the first electron transport layer is the distance between the opposite side surfaces of the first electron transport layer close to the first electrode and away from the first electrode, and the thickness of the second electron transport layer is the distance between the opposite side surfaces of the second electron transport layer close to the first electrode and away from the first electrode.

[0012] In example embodiments, the second electron transport layer has a thickness greater than or equal to 30 nm and less than or equal to 120 nm.

[0013] In an exemplary embodiment, an insertion layer is further included between the first electron transport layer and the second electron transport layer, wherein the conduction band bottom energy level of the insertion layer is greater than the conduction band bottom energy level of the first electron transport layer, and the carrier mobility of the insertion layer is less than the carrier mobility of the second electron transport layer.

[0014] In an exemplary embodiment, the material of the insertion layer includes any one of poly[(9,9-dioctylfluorene-2,7-diyl)-co-(4,4′-(N-(4-sec-butylphenyl)diphenylamine)], polyvinylcarbazole, and poly[bis(4-phenyl)(4-butylphenyl)amine].

[0015] In an exemplary embodiment, a capping layer is further included and is disposed on a side of the second electrode away from the quantum dot light emitting layer.

[0016] In an exemplary embodiment, one of the first electrode and the second electrode is a transmissive electrode, and the other is a reflective electrode.

[0017] In a second aspect, an embodiment of the present invention provides a display substrate comprising a plurality of light-emitting devices, at least one of which comprises the quantum dot light-emitting diode as described above.

[0018] In an exemplary embodiment, the plurality of light-emitting devices includes a red light-emitting device, and the sum of the thicknesses of the first electron transport layer and the second electron transport layer of the red light-emitting device is greater than or equal to 100 nm and less than or equal to 190 nm.

[0019] In an exemplary embodiment, the thickness of the second electron transport layer of the red light emitting device is greater than or equal to 60 nm and less than or equal to 150 nm.

[0020] In an exemplary embodiment, the plurality of light-emitting devices includes a green light-emitting device, and the sum of the thicknesses of the first electron transport layer and the second electron transport layer of the green light-emitting device is greater than or equal to 80 nm and less than or equal to 180 nm.

[0021] In an exemplary embodiment, the thickness of the second electron transport layer of the green light-emitting device is greater than or equal to 40 nm and less than or equal to 140 nm.

[0022] In an exemplary embodiment, the plurality of light-emitting devices includes a blue light-emitting device, and the sum of the thicknesses of the first electron transport layer and the second electron transport layer of the blue light-emitting device is greater than or equal to 70 nm and less than or equal to 170 nm.

[0023] In an exemplary embodiment, the thickness of the second electron transport layer of the blue light-emitting device is greater than or equal to 30 nm and less than or equal to 130 nm.

[0024] In a third aspect, an embodiment of the present invention provides a display device, comprising the display substrate as described above.

[0025] The quantum dot light-emitting diode provided by the present invention adds a second electron transport layer with stronger conductivity to the side of the quantum dot light-emitting layer near the second electrode. The thickness of the second electron transport layer can be used to control the length of the optical microcavity between the first and second electrodes, thereby ensuring that the optical microcavity length of the QLED is within a range that enhances the wavelength of emitted light, thereby improving the light output of the QLED. When the quantum dot light-emitting diode provided by the present invention is applied to a display substrate, it helps to improve the light output from the front of the display substrate.

[0026] Other features and advantages of the present invention will be described in the following description, and in part will become apparent from the description, or understood by practicing the present invention. The purpose and other advantages of the present invention can be achieved and obtained through the structures particularly pointed out in the description and the drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] The accompanying drawings are used to provide a further understanding of the technical solution of the present invention and constitute a part of the specification. Together with the embodiments of the present application, they are used to explain the technical solution of the present invention and do not constitute a limitation on the technical solution of the present invention.

[0028] Figure 1 is a structural schematic diagram of a display device;

[0029] Figure 2 A schematic diagram of the planar structure of a display substrate;

[0030] Figure 3 is an equivalent circuit diagram of a pixel driving circuit;

[0031] Figure 4 A schematic diagram of the cross-sectional structure of a display substrate;

[0032] Figure 5 A schematic diagram of the structure of a QLED provided by at least one embodiment of the present invention;

[0033] Figure 6 Schematic diagram of the energy level relationship of QLED in Example 1;

[0034] Figure 7 Graph showing the relationship between light distribution and viewing angle for a top-emitting display substrate using the QLED in Example 1 as a light-emitting device;

[0035] Figure 8 Graph showing the relationship between light distribution and viewing angle of a top-emitting display substrate using QLED as a light-emitting device in a comparative example of Example 1. DETAILED DESCRIPTION

[0036] The following is a detailed description of the embodiments of the present invention in conjunction with the accompanying drawings. The embodiments can be implemented in a variety of different forms. A person skilled in the art can easily understand that the method and content can be transformed into other forms without departing from the purpose and scope of the present invention. Therefore, the present invention should not be interpreted as being limited to the contents described in the following embodiments. In the absence of conflict, the embodiments of the present invention and the features in the embodiments can be combined with each other in any way.

[0037] In the accompanying drawings, the size of one or more components, the thickness of a layer, or the area is sometimes exaggerated for the sake of clarity. Therefore, one embodiment of the present invention is not necessarily limited to this size, and the shape and size of one or more components in the accompanying drawings do not reflect the true proportions. In addition, the accompanying drawings schematically illustrate ideal examples, and one embodiment of the present invention is not limited to the shapes or values ​​shown in the accompanying drawings. The proportions of the drawings in the present invention can be used as a reference in actual processes, but are not limited to this. For example: the width-to-length ratio of the channel, the thickness and spacing of the film layers, and the width and spacing of the signal lines can be adjusted according to actual needs.

[0038] The ordinal numbers such as "first", "second", and "third" in this specification are provided to avoid confusion among constituent elements, and are not intended to limit the quantity. The "plurality" in this utility model means two or more.

[0039] In this specification, for convenience, words and phrases indicating orientation or positional relationships, such as "middle," "upper," "lower," "front," "back," "vertical," "horizontal," "top," "bottom," "inside," and "outside," are used to illustrate the positional relationships of components with reference to the accompanying drawings. This is solely for the purpose of facilitating the description of this specification and simplifying the description. They are not intended to indicate or imply that the device or component referred to must have a specific orientation, be constructed, or operate in a specific orientation. Therefore, they should not be construed as limitations on the present invention. The positional relationships of the components may be appropriately modified depending on the orientation of the components being described. Therefore, the present invention is not limited to the words and phrases described in the specification and may be appropriately modified depending on the circumstances.

[0040] In this specification, unless otherwise clearly specified and limited, the terms "installed", "connected" and "connected" should be understood in a broad sense. For example, it can be a fixed connection, or a detachable connection, or an integral connection; it can be a mechanical connection, or an electrical connection; it can be a direct connection, or an indirect connection through an intermediate piece, or a connection between the two elements. For those of ordinary skill in the art, the meaning of the above terms in this utility model can be understood according to the circumstances. Among them, "electrical connection" includes the situation where constituent elements are connected together through an element with some electrical function. There is no special restriction on "elements with some electrical function" as long as they can transmit electrical signals between connected constituent elements. Examples of "elements with some electrical function" include not only electrodes and wiring, but also switching elements such as transistors, resistors, inductors, capacitors, and other elements with one or more functions.

[0041] In this specification, a transistor refers to a device that includes at least three terminals: a gate electrode, a drain electrode, and a source electrode. A transistor has a channel region between a drain electrode (drain electrode terminal, drain region, or drain) and a source electrode (source electrode terminal, source region, or source), and current can flow through the drain electrode, the channel region, and the source electrode. In this specification, the channel region refers to the region through which current primarily flows.

[0042] In this specification, in order to distinguish the two poles of a transistor other than the gate, one of the electrodes is referred to as the first electrode and the other electrode is referred to as the second electrode. For example, the first electrode can be a drain electrode and the second electrode can be a source electrode, or the first electrode can be a source electrode and the second electrode can be a drain electrode. In cases where transistors with opposite polarities are used or where the direction of current changes during circuit operation, the functions of the "source electrode" and the "drain electrode" are sometimes interchangeable. Therefore, in this specification, the "source electrode" and the "drain electrode" can be interchangeable, and the "source terminal" and the "drain terminal" can be interchangeable.

[0043] In this specification, "parallel" refers to a state where the angle formed by two straight lines is greater than -10° and less than 10°, and thus also includes a state where the angle is greater than -5° and less than 5°. Furthermore, "perpendicular" refers to a state where the angle formed by two straight lines is greater than 80° and less than 100°, and thus also includes a state where the angle is greater than 85° and less than 95°.

[0044] In this specification, triangles, rectangles, trapezoids, pentagons or hexagons are not in the strict sense, but may be approximate triangles, rectangles, trapezoids, pentagons or hexagons, etc. There may be some small deformations caused by tolerances, and there may be chamfers, arc edges and deformations.

[0045] The term "about" in this specification refers to a numerical value that is not strictly limited and allows for process and measurement errors.

[0046] In this specification, "A extends along direction B" means that A can include a main portion and a secondary portion connected to the main portion, the main portion being a line, line segment, or strip, extending along direction B, and the length of the main portion extending along direction B being greater than the length of the secondary portion extending along other directions. In the following description, "A extends along direction B" means "the main portion of A extends along direction B."

[0047] In this specification, “A and B are provided in the same layer” means that A and B are formed simultaneously through the same patterning process when preparing the display substrate.

[0048] In addition, when describing representative embodiments, the specification may have presented the method and / or process as a specific sequence of steps. However, to the extent that the method or process does not rely on the specific order of the steps described herein, the method or process should not be limited to the steps in the specific order described. As will be understood by those skilled in the art, other orders of steps are also possible. Therefore, the specific order of the steps set forth in the specification should not be interpreted as a limitation on the claims. In addition, the claims to the method and / or process should not be limited to performing their steps in the order written, and those skilled in the art can readily understand that these orders can be changed and still remain within the spirit and scope of the embodiments of the present invention.

[0049] QLEDs consist of an anode, a cathode, and a light-emitting layer positioned between them. Their light-emitting principle is that holes and electrons are injected into the light-emitting layer from the anode and cathode, respectively. When the electrons and holes meet in the light-emitting layer, they recombine to produce excitons. These excitons emit light as they transition from an excited state to a ground state. QLEDs are widely used in display panels and lighting applications.

[0050] Figure 1 FIG. 1 is a schematic diagram of the structure of a display device. Figure 1As shown, the display device may include: a scan signal driver, a data signal driver, a light emitting signal driver, a display substrate, a first power supply unit, a second power supply unit and an initial power supply unit. In some exemplary embodiments, the display substrate includes at least a plurality of scan signal lines (S(1) to S(N)), a plurality of data signal lines (D(1) to D(M)) and a plurality of light emitting signal lines (EM(1) to EM(N)). The scan signal driver is configured to sequentially provide scan signals to the plurality of scan signal lines (S(1) to S(N)), the data signal driver is configured to provide data signals to the plurality of data signal lines (D(1) to D(M)), and the light emitting signal driver is configured to sequentially provide light emitting control signals to the plurality of light emitting signal lines (EM(1) to EM(N)). In some exemplary embodiments, the plurality of scan signal lines and the plurality of light emitting signal lines extend in a horizontal direction, and the plurality of data signal lines extend in a vertical direction. The display substrate includes a plurality of sub-pixels, and one sub-pixel includes a pixel driving circuit and a light emitting device. The pixel driving circuit is connected to the scan signal lines, the light-emission control lines, and the data signal lines. Under the control of the scan signal lines and the light-emission signal lines, the pixel driving circuit is configured to receive a data voltage transmitted by the data signal lines and output a corresponding current to the light-emitting device. The light-emitting device is connected to the pixel driving circuit and is configured to emit light of a corresponding brightness in response to the current output by the pixel driving circuit. The first power supply unit, the second power supply unit, and the initial power supply unit are respectively configured to provide a first power supply voltage, a second power supply voltage, and an initial power supply voltage to the pixel driving circuit via the first power line, the second power line, and the initial signal line.

[0051] Figure 2 FIG. 1 is a schematic diagram of a planar structure of a display substrate. Figure 2 As shown, the display area of ​​the display substrate may include a plurality of pixel units P arranged in a matrix. At least one of the plurality of pixel units P includes a first sub-pixel P1 that emits a first color light, a second sub-pixel P2 that emits a second color light, and a third sub-pixel P3 that emits a third color light. The first sub-pixel P1, the second sub-pixel P2, and the third sub-pixel P3 each include a pixel driving circuit and a light-emitting device. In some exemplary embodiments, the pixel unit P may include a red (R) sub-pixel, a green (G) sub-pixel, and a blue (B) sub-pixel, or may include a red sub-pixel, a green sub-pixel, a blue sub-pixel, and a white (W) sub-pixel, but this is not limited in the present invention. In some exemplary embodiments, the shape of the sub-pixels in the pixel unit may be rectangular, diamond-shaped, pentagonal, or hexagonal. When the pixel unit includes three sub-pixels, the three sub-pixels may be arranged horizontally, vertically, or in a triangular pattern. When the pixel unit includes four sub-pixels, the four sub-pixels may be arranged horizontally, vertically, or in a square pattern. However, this is not limited in the present invention.

[0052] In some example embodiments, the pixel driving circuit may be a 3T1C, 4T1C, 5T1C, 5T2C, 6T1C, or 7T1C structure. Figure 3 is an equivalent circuit diagram of a pixel driving circuit. Figure 3 As shown, the pixel driving circuit may include 7 switching transistors (first transistor T1 to seventh transistor T7), 1 storage capacitor C, and 8 signal lines (data signal line DATA, first scan signal line S1, second scan signal line S2, first initial signal line INIT1, second initial signal line INIT2, first power line VSS, second power line VDD, and light-emitting signal line EM). The first initial signal line INIT1 and the second initial signal line INIT2 may be the same signal line.

[0053] In some exemplary embodiments, a control electrode of the first transistor T1 is connected to the second scan signal line S2, a first electrode of the first transistor T1 is connected to the first initial signal line INIT1, and a second electrode of the first transistor T1 is connected to the second node N2. A control electrode of the second transistor T2 is connected to the first scan signal line S1, a first electrode of the second transistor T2 is connected to the second node N2, and a second electrode of the second transistor T2 is connected to the third node N3. A control electrode of the third transistor T3 is connected to the second node N2, a first electrode of the third transistor T3 is connected to the first node N1, and a second electrode of the third transistor T3 is connected to the third node N3. A control electrode of the fourth transistor T4 is connected to the first scan signal line S1, a first electrode of the fourth transistor T4 is connected to the data signal line DATA, and a second electrode of the fourth transistor T4 is connected to the first node N1. A control electrode of the fifth transistor T5 is connected to the emission signal line EM, a first electrode of the fifth transistor T5 is connected to the second power supply line VDD, and a second electrode of the fifth transistor T5 is connected to the first node N1. A control electrode of the sixth transistor T6 is connected to the light emitting signal line EM, a first electrode of the sixth transistor T6 is connected to the third node N3, and a second electrode of the sixth transistor T6 is connected to the first electrode of the light emitting device. A control electrode of the seventh transistor T7 is connected to the first scan signal line S1, a first electrode of the seventh transistor T7 is connected to the second initial signal line INIT2, and a second electrode of the seventh transistor T7 is connected to the first electrode of the light emitting device. A first end of the storage capacitor C is connected to the second power supply line VDD, and a second end of the storage capacitor C is connected to the second node N2.

[0054] In some exemplary embodiments, the first transistor T1 to the seventh transistor T7 may be a P-type transistor or an N-type transistor. Using the same type of transistors in the pixel driving circuit can simplify the process flow, reduce the manufacturing difficulty of the display panel, and improve the product yield. In some possible implementations, the first transistor T1 to the seventh transistor T7 may include P-type transistors and N-type transistors.

[0055] In some exemplary embodiments, the second electrode of the light-emitting device is connected to a first power line VSS. The signal of the first power line VSS is a low-level signal, and the signal of the second power line VDD is a continuously high-level signal. The first scan signal line S1 is a scan signal line in the pixel drive circuit of the current display row, and the second scan signal line S2 is a scan signal line in the pixel drive circuit of the previous display row. That is, for the nth display row, the first scan signal line S1 is S(n), and the second scan signal line S2 is S(n-1). The second scan signal line S2 of the current display row is the same as the first scan signal line S1 in the pixel drive circuit of the previous display row, which can reduce the number of signal lines in the display panel and achieve a narrow bezel of the display panel.

[0056] Figure 4 FIG. 1 is a schematic diagram of a cross-sectional structure of a display substrate, illustrating the structure of three sub-pixels of the display substrate. Figure 4 As shown, on a plane perpendicular to the display substrate, the display substrate may include a driving circuit layer 102 disposed on a substrate 101, a light-emitting device 103 disposed on a side of the driving circuit layer 102 away from the substrate 101, and an encapsulation layer 104 disposed on a side of the light-emitting device 103 away from the substrate 101. In some possible implementations, the display substrate may include other film layers, such as spacers, etc., which are not limited in this invention.

[0057] In some exemplary embodiments, the substrate 101 may be a flexible substrate or a rigid substrate. The flexible substrate may include a first flexible material layer, a first inorganic material layer, a semiconductor layer, a second flexible material layer, and a second inorganic material layer stacked together. The first flexible material layer and the second flexible material layer may be made of polyimide (PI), polyethylene terephthalate (PET), or a surface-treated polymer soft film. The first inorganic material layer and the second inorganic material layer may be made of silicon nitride (SiNx) or silicon oxide (SiOx) to improve the substrate's resistance to water and oxygen. The semiconductor layer may be made of amorphous silicon (a-Si).

[0058] In some exemplary embodiments, the driving circuit layer 102 of each sub-pixel may include a plurality of transistors and storage capacitors constituting a pixel driving circuit. Figure 4In the example, each sub-pixel includes a driving transistor and a storage capacitor. In some possible implementations, the driving circuit layer 102 of each sub-pixel may include: a first insulating layer 201 disposed on a substrate; an active layer disposed on the first insulating layer; a second insulating layer 202 covering the active layer; a gate electrode and a first capacitor electrode disposed on the second insulating layer 202; a third insulating layer 203 covering the gate electrode and the first capacitor electrode; a second capacitor electrode disposed on the third insulating layer 203; a fourth insulating layer 204 covering the second capacitor electrode, with vias provided in the second insulating layer 202, the third insulating layer 203, and the fourth insulating layer 204 exposing the active layer; a source electrode and a drain electrode disposed on the fourth insulating layer 204, with the source electrode and the drain electrode respectively connected to the active layer through the vias; and a planar layer 205 covering the aforementioned structure, with a via provided in the planar layer 205 exposing the drain electrode. The active layer, gate electrode, source electrode, and drain electrode constitute the driving transistor 210, and the first capacitor electrode and the second capacitor electrode constitute the storage capacitor 211.

[0059] In some exemplary embodiments, the light-emitting device 103 may include an anode 301, a pixel definition layer 302, a light-emitting functional layer 303, and a cathode 304. The anode 301 is disposed on the planar layer 205 and is connected to the drain electrode of the driving transistor 210 through a via hole provided in the planar layer 205. The pixel definition layer 302 is disposed on the anode 301 and the planar layer 205, and a pixel opening is provided on the pixel definition layer 302, exposing the anode 301. The light-emitting functional layer 303 is at least partially disposed within the pixel opening and is connected to the anode 301. The cathode 304 is disposed on the light-emitting functional layer 303 and is connected to the light-emitting functional layer 303. The light-emitting functional layer 303 emits light of a corresponding color when driven by the anode 301 and the cathode 304.

[0060] In some exemplary embodiments, the encapsulation layer 104 may include a stacked first encapsulation layer 401, a second encapsulation layer 402, and a third encapsulation layer 403. The first encapsulation layer 401 and the third encapsulation layer 403 may be made of inorganic materials, and the second encapsulation layer 402 may be made of organic materials. The second encapsulation layer 402 is disposed between the first encapsulation layer 401 and the third encapsulation layer 403 to prevent external moisture from entering the light-emitting device 103.

[0061] In some exemplary embodiments, the light-emitting functional layer of the light-emitting device may include a light-emitting layer (EML), and one or more film layers selected from the group consisting of a hole injection layer (HIL), a hole transport layer (HTL), a hole blocking layer (HBL), an electron blocking layer (EBL), an electron injection layer (EIL), and an electron transport layer (ETL). Driven by the voltage of the anode and cathode, the light-emitting properties of the quantum dot material are utilized to emit light according to the required grayscale.

[0062] In some exemplary embodiments, the light-emitting layers of QLED light-emitting devices of different colors are different. For example, a red light-emitting device includes a red light-emitting layer, a green light-emitting device includes a green light-emitting layer, and a blue light-emitting device includes a blue light-emitting layer. In order to reduce the difficulty of the process and improve the yield, the hole injection layer and the hole transport layer on one side of the light-emitting layer can use a common layer, and the electron injection layer and the electron transport layer on the other side of the light-emitting layer can use a common layer. In some exemplary embodiments, any one or more layers of the hole injection layer, the hole transport layer, the electron injection layer and the electron transport layer can be made by a single process (a single evaporation process or a single inkjet printing process), but isolation is achieved by means of a surface step difference of the formed film layer or by surface treatment. For example, any one or more layers of the hole injection layer, the hole transport layer, the electron injection layer and the electron transport layer corresponding to adjacent sub-pixels can be isolated. In some exemplary embodiments, the light-emitting functional layer can be formed by evaporation using a fine metal mask (FMM) or an open mask (Open Mask), or by scraping, spin coating and inkjet processes.

[0063] Combine Figure 4 As shown, a display substrate in which the light emitted by the light-emitting device 103 is emitted from the side of the substrate 101 is called a bottom-emitting display substrate. Since the circuits and transistors are distributed on the side of the light-emitting device 103 close to the substrate 101, the aperture ratio of the sub-pixels is low, and the brightness of the display substrate is low. On the other hand, a display substrate in which the light emitted by the light-emitting device 103 is emitted from the side of the encapsulation layer 104 is called a top-emitting display substrate. The emitted light is not affected by the circuits and transistors, the aperture ratio of the sub-pixels is large, and the brightness of the display substrate is high. In addition, for a top-emitting display substrate, the microcavity effect between the anode 301 and the cathode 304 of the light-emitting device 103 can be used to control the angle of the emitted light, enhance the light emission of the display substrate, and achieve a better display effect.

[0064] An embodiment of the present utility model provides a quantum dot light-emitting diode, comprising: a first electrode, a second electrode, and a quantum dot light-emitting layer, a first electron transport layer, and a second electron transport layer arranged between the first electrode and the second electrode, wherein the first electron transport layer and the second electron transport layer are sequentially arranged on a side of the quantum dot light-emitting layer close to the second electrode; wherein the materials of the first electron transport layer and the second electron transport layer include inorganic nanoparticles, the conduction band bottom energy level of the first electron transport layer matches the conduction band bottom energy level of the quantum dot light-emitting layer, the conduction band bottom energy level of the second electron transport layer is greater than the work function of the second electrode and less than the conduction band bottom energy level of the first electron transport layer; the carrier mobility of the second electron transport layer is greater than the carrier mobility of the first electron transport layer, and the second electron transport layer is configured to adjust the length of the optical microcavity between the first electrode and the second electrode.

[0065] The quantum dot light-emitting diode provided by the present invention adds a second electron transport layer with higher conductivity to the side of the quantum dot light-emitting layer near the second electrode. The thickness of the second electron transport layer can be used to control the length of the optical microcavity between the first and second electrodes, thereby ensuring that the optical microcavity length of the QLED is within a range that enhances the wavelength of emitted light, thereby improving the light output of the QLED. When the quantum dot light-emitting diode provided by the present invention is applied to a display substrate, it helps to improve the light output from the front of the display substrate.

[0066] In an exemplary embodiment, the conduction band bottom energy level of the first electron transport layer matches the conduction band bottom energy level of the quantum dot light-emitting layer, including: the difference between the conduction band bottom energy level of the first electron transport layer and the conduction band bottom energy level of the quantum dot light-emitting layer is less than or equal to 0.5 eV.

[0067] Figure 5 This is a schematic diagram of the structure of a QLED provided by at least one embodiment of the present invention. Figure 5As shown, the QLED provided in this embodiment includes: a first electrode 10, a second electrode 12, and a quantum dot light-emitting layer 40, a first electron transport layer 51, and a second electron transport layer 52 disposed between the first electrode 10 and the second electrode 12. The first electron transport layer 51 and the second electron transport layer 52 are sequentially disposed on the side of the quantum dot light-emitting layer 40 near the second electrode 12. The materials of the first electron transport layer 51 and the second electron transport layer 52 include inorganic nanoparticles. The conduction band bottom energy level (LUMO energy level) of the first electron transport layer 51 matches the conduction band bottom energy level of the quantum dot light-emitting layer 40. The conduction band bottom energy level of the second electron transport layer 52 is greater than the work function of the second electrode 12 and less than the conduction band bottom energy level of the first electron transport layer 51. The second electron transport layer 52 is configured to adjust the length of the optical microcavity between the first electrode and the second electrode. In an exemplary embodiment, the quantum dot light-emitting layer 40 is configured to cause electrons and holes to recombine and emit light. The first electrode 10 may be an anode, the second electrode 12 may be a cathode, the anode of the QLED may be a transmissive anode, the cathode of the QLED may be a reflective cathode, and the light emitted by the QLED may be emitted through the anode, or the anode of the QLED may be a reflective anode, the cathode of the QLED may be a transmissive cathode, and the light emitted by the QLED may be emitted through the cathode, or both the anode and cathode of the QLED may be transmissive electrodes, and the light emitted by the QLED may be emitted from the anode and the cathode.

[0068] In an exemplary embodiment, the energy level of the material of the first electron transport layer 51 can match the energy level of the quantum dot light-emitting layer 40, and the second electron transport layer 52 can be made of a highly conductive material. The length of the optical microcavity between the first electrode 10 and the second electrode 12 can be adjusted by controlling the thickness of the second electron transport layer 52, so that the length of the optical microcavity of the QLED is in a length range that enhances the wavelength of the emitted light, and the thickness of each functional layer can be matched under optimal electrical performance, effectively coordinating the optical performance and electrical performance of the QLED, which helps to improve the light emission and working performance of the QLED. In the embodiment of the present invention, by controlling the thickness of the second electron transport layer 52, the length of the optical microcavity can meet the cavity length of the first-order microcavity, and can even reach the length of the second-order microcavity. In the embodiment of the present invention, the thickness of the film layer "A" can be the distance between the surface of the side of the film layer "A" close to the first electrode 10 and the surface of the side away from the first electrode 10, such as Figure 5 As shown, the thickness of the second electron transport layer 52 may be a distance D52 between a surface of the second electron transport layer 52 on one side close to the first electrode 10 and a surface of the second electron transport layer 52 on the other side away from the first electrode 10 .

[0069] In example embodiments, the conduction band bottom energy level of the first electron transport layer 51 may be greater than or equal to −4.5 electron volts (eV) and less than or equal to −3 eV.

[0070] In exemplary embodiments, the first electron transport layer 51 may have a carrier mobility greater than or equal to 1*10 −4 square centimeters per volt-second (cm 2 / V*s) and less than or equal to 1*10 −2 cm 2 / V*s.

[0071] In an exemplary embodiment, the material of the first electron transport layer 51 includes magnesium (Mg)-doped zinc oxide (ZnO) nanoparticles.

[0072] In example embodiments, the molar ratio of Mg in the first electron transport layer 51 may be greater than or equal to 5% and less than or equal to 15%. The molar ratio of Mg in the first electron transport layer 51 may be a ratio of the amount of Mg to the amount of Zn in the first electron transport layer 51.

[0073] In example embodiments, the sum of the thicknesses of the first electron transport layer and the second electron transport layer is greater than or equal to 70 nm and less than or equal to 190 nm.

[0074] In example embodiments, the thickness of the first electron transport layer 51 may be greater than or equal to 40 nm and less than or equal to 70 nm.

[0075] In example embodiments, the conduction band bottom energy level of the second electron transport layer 52 may be greater than or equal to −4.5 eV and less than or equal to −3.1 eV.

[0076] In an exemplary embodiment, the carrier mobility of the second electron transport layer 52 may be greater than or equal to 1*10-4 cm2 / V*s and less than or equal to 1*10-2 cm2 / V*s. The greater carrier mobility and greater conductivity of the second electron transport layer 52 facilitate flexible adjustment of the thickness of the second electron transport layer 52.

[0077] In an exemplary embodiment, the material of the second electron transport layer 52 includes N-type doped ZnO nanoparticles. In this embodiment, particles of the doping element are embedded in the lattice of the ZnO nanoparticles to form a new material, which helps improve the conductivity of the ZnO nanoparticles themselves.

[0078] In an exemplary embodiment, the doping elements of the second electron transport layer 52 may include trivalent elements, such as boron (B), aluminum (Al), gallium (Ga), indium (In), etc., and may also include tetravalent elements, such as silicon (Si), etc., which is not limited in the present invention.

[0079] In an exemplary embodiment, the molar ratio of the doping element in the second electron transport layer 52 may be greater than or equal to 0.1% and less than or equal to 15%. In this embodiment, the molar ratio of the doping element in the second electron transport layer 52 may be a ratio of the amount of the doping element to the amount of Zn in the second electron transport layer 52.

[0080] In example embodiments, the second electron transport layer 52 may have a thickness greater than or equal to 30 nm and less than or equal to 120 nm.

[0081] In an exemplary embodiment, Figure 5 As shown, the QLED further includes an insertion layer 60 disposed between the first electron transport layer 51 and the second electron transport layer 52. The conduction band bottom energy level of the insertion layer 60 is greater than the conduction band bottom energy level of the first electron transport layer 51, and the carrier mobility of the insertion layer 60 is less than the carrier mobility of the second electron transport layer 52. The provision of the insertion layer 60 prevents the second electron transport layer 52 from dissolving into the first electron transport layer 51 during the preparation process, thereby protecting the first electron transport layer 51.

[0082] In an exemplary embodiment, the carrier mobility of the insertion layer 60 may be less than 1*10-2 cm2 / V*s. The insertion layer 60 may serve as an electron tunneling layer, controlling the magnitude of the injected electron current and promoting lateral expansion of the current.

[0083] In exemplary embodiments, the thickness of the insertion layer 60 may be greater than or equal to 0.1 nm and less than or equal to 5 nm.

[0084] In an exemplary embodiment, the insertion layer 60 may be made of an organic material. For example, the insertion layer 60 may be a thin film formed of an organic high molecular polymer. The insertion layer 60 of such a material may be prepared by a solution method, which is simple and applicable to devices of different structures.

[0085] In an exemplary embodiment, the material of the insertion layer 60 may include any one of poly[(9,9-dioctylfluorene-2,7-diyl)-co-(4,4′-(N-(4-sec-butylphenyl)diphenylamine)], polyvinylcarbazole, and poly[bis(4-phenyl)(4-butylphenyl)amine].

[0086] In an exemplary embodiment, Figure 5 As shown, the QLED further includes a capping layer (CPL) 13 disposed on a side of the second electrode 12 away from the quantum dot light-emitting layer 40. The capping layer 13 helps reduce light loss and improve the light efficiency, power efficiency and product life of the QLED.

[0087] In an exemplary embodiment, Figure 5As shown, the QLED further includes a hole injection layer 20 and a hole transport layer 30 arranged on a side of the quantum dot light-emitting layer 40 close to the first electrode 10 . The hole injection layer 20 is located on a side of the hole transport layer 30 close to the first electrode 10 .

[0088] In an exemplary embodiment, Figure 5 The QLED shown is used in Figure 4 In the case of the display substrate shown, the anode of the QLED can face the substrate 101, and the cathode of the QLED is located on the side away from the substrate 101. This structure can be called an upright structure. In other embodiments, the cathode of the QLED can face the substrate 101, and the anode of the QLED is located on the side away from the substrate 101. This structure can be called an inverted structure. The QLED provided by the embodiment of the present invention can be used in both an upright structure and an inverted structure. For example, the insertion layer 60 of the organic material can be successfully formed by a solution method in both the upright structure and the inverted structure, and the present invention does not impose any restrictions on this.

[0089] The QLED provided by the present invention is introduced below with reference to several specific embodiments.

[0090] Example 1

[0091] In an exemplary embodiment, the anode of the QLED may be indium tin oxide (ITO), the thickness of the hole injection layer 20 may be approximately 30 nm, the thickness of the hole transport layer 30 may be approximately 25 nm, the quantum dot light-emitting layer 40 may emit green light, the thickness of the quantum dot light-emitting layer 40 may be approximately 20 nm, the material of the first electron transport layer 51 may be Mg-doped ZnO, the molar ratio of Mg is approximately 10%, the thickness of the first electron transport layer 51 is approximately 60 nm, the material of the insertion layer 60 may be poly[(9,9-dioctylfluorene-2,7-diyl)-co-(4,4′-(N-(4-sec-butylphenyl)diphenylamine)](TFB), the thickness of the insertion layer 60 is approximately 1 nm, the material of the second electron transport layer 52 may be Al-doped ZnO, the molar ratio of Al is approximately 5%, the thickness of the second electron transport layer 52 is approximately 60 nm, the material of the second electrode 12 may be metal, the thickness of the second electrode 12 is approximately 10 nm, and the thickness of the covering layer 13 is approximately 60 nm.

[0092] In an exemplary embodiment, the hole injection layer 20, the hole transport layer 30, the quantum dot light-emitting layer 40, the first electron transport layer 51, the insertion layer 60 and the second electron transport layer 52 in this embodiment can all be prepared by spin coating, scraping, inkjet printing and other methods, and the present invention does not impose any restrictions on this.

[0093] Figure 6Schematic diagram of the energy level relationship of the QLED in Example 1, illustrating the positional relationship between the Fermi level EF10 of the first electrode 10, the Fermi level EF12 of the second electrode 12, and the conduction band bottom energy level and the valence band top energy level (HOMO energy level) of other film layers located between the first electrode 10 and the second electrode 12. Figure 6 As shown, the conduction band bottom energy level LUMO51 of the first electron transport layer 51 matches the conduction band bottom energy level LUMO40 of the quantum dot light-emitting layer 40, and the conduction band bottom energy level LUMO52 of the second electron transport layer 52 is greater than or equal to the conduction band bottom energy level LUMO51 of the first electron transport layer 51, and less than or equal to the Fermi level EF12 of the second electrode 12. The conduction band bottom energy level LUMO60 of the insertion layer 60 is greater than the conduction band bottom energy level LUMO51 of the first electron transport layer 51.

[0094] Figure 7 : This is a diagram showing the relationship between light distribution and viewing angle of a top-emitting display substrate using the QLED in Example 1 as a light-emitting device. Figure 7 As shown, the ordinate I represents light intensity, the abscissa represents the light-emitting surface of the display substrate, and the radially distributed lines represent different viewing angles facing the light-emitting surface of the display substrate. Points located on different viewing angle lines represent the light intensity I at that viewing angle. The solid lines connecting the points on the different viewing angle lines represent the light distribution facing the display substrate. In a top-emitting display substrate using the QLEDs described in Example 1 as light-emitting devices, the light emitted by the display substrate is concentrated in the direction directly facing the screen. The light intensity in this direction is higher, which is convenient for users to watch and helps save power consumption of the display substrate.

[0095] Comparative Example of Example 1

[0096] In an exemplary embodiment, the difference between this comparative example and Example 1 is that the insertion layer 60 and the second electron transport layer 52 are not provided, and the remaining structures and parameter settings are the same as those of Example 1 and are not repeated here.

[0097] Figure 8 : is a diagram showing the relationship between light distribution and viewing angle of a top-emitting display substrate using QLED as a light-emitting device in a comparative example of Example 1. Figure 8 Display substrate and Figure 7 The difference in display substrates is only the QLED used. Figure 8 As shown, without the insertion layer 60 and the second electron transport layer 52, the lateral light emission of the display substrate is significantly enhanced, which is not conducive to the power consumption of the display substrate and the user experience is not good. Figure 7 and Figure 8 It can be seen that by providing the insertion layer 60 and the second electron transport layer 52 , the length of the optical microcavity can be adjusted, thereby adjusting the light output angle and enhancing the light output, thereby improving the display effect of the display substrate.

[0098] Example 2

[0099] In the exemplary embodiment, the difference between the second embodiment and the first embodiment is that the material of the insertion layer 60 is different, and the materials and parameters of the remaining structures are the same as those of the first embodiment, which will not be repeated here.

[0100] In an exemplary embodiment, the material of the insertion layer 60 in this embodiment may be polyvinyl carbazole (PVK), and the thickness of the insertion layer 60 may be set as needed, which is not limited in the present invention.

[0101] Example 3

[0102] In the exemplary embodiment, the difference between the third embodiment and the first embodiment is that the material of the insertion layer 60 is different, and the materials and parameters of the remaining structures are the same as those of the first embodiment, which will not be repeated here.

[0103] In an exemplary embodiment, the material of the insertion layer 60 in this embodiment can be poly-bis(4-phenyl)(4-butylphenyl)amine] (Poly-TPD), and the thickness of the insertion layer 60 can be set as needed, which is not limited by the present invention.

[0104] Example 4

[0105] In the exemplary embodiment, the difference between the fourth embodiment and the first embodiment lies in the different materials of the second electron transport layer 52 , and the materials and parameters of the remaining structures are the same as those of the first embodiment, which will not be described again.

[0106] In an exemplary embodiment, the material of the second electron transport layer 52 in this embodiment may be Ga-doped ZnO, and the thickness of the second electron transport layer 52 may be set as needed, which is not limited in the present invention.

[0107] Example 5

[0108] In an exemplary embodiment, the difference between the fifth embodiment and the fourth embodiment is that the quantum dot light-emitting layer 40 emits red light, and the materials and parameters of the remaining structures are the same as those of the fourth embodiment, which will not be repeated here.

[0109] Example 6

[0110] In an exemplary embodiment, the difference between Example 6 and Example 4 is that the quantum dot light-emitting layer 40 emits blue light, and the materials and parameters of the remaining structures are the same as those of Example 4 and are not described again here.

[0111] An embodiment of the present invention provides a display substrate comprising a plurality of light-emitting devices, at least one of which comprises the quantum dot light-emitting diode as described above.

[0112] In an exemplary embodiment, the plurality of light-emitting devices includes a red light-emitting device, and the sum of the thicknesses of the first electron transport layer and the second electron transport layer of the red light-emitting device is greater than or equal to 100 nm and less than or equal to 190 nm.

[0113] In an exemplary embodiment, the thickness of the second electron transport layer of the red light-emitting device is greater than or equal to 60 nm and less than or equal to 150 nm. By adjusting the sum of the thicknesses of the first and second electron transport layers of the red light-emitting device, as well as the thickness of the second electron transport layer of the red light-emitting device, the optical microcavity of the red light-emitting device can produce a strong resonance with red light, thereby improving the light output intensity of the red light-emitting device.

[0114] In an exemplary embodiment, the plurality of light-emitting devices includes a green light-emitting device, and the sum of the thicknesses of the first electron transport layer and the second electron transport layer of the green light-emitting device is greater than or equal to 80 nm and less than or equal to 180 nm.

[0115] In an exemplary embodiment, the thickness of the second electron transport layer of the green light-emitting device is greater than or equal to 40 nm and less than or equal to 140 nm. By adjusting the sum of the thicknesses of the first and second electron transport layers of the green light-emitting device, as well as the thickness of the second electron transport layer of the green light-emitting device, the optical microcavity of the green light-emitting device can produce a strong resonance with the green light, thereby improving the light output intensity of the green light-emitting device.

[0116] In an exemplary embodiment, the plurality of light-emitting devices includes a blue light-emitting device, and the sum of the thicknesses of the first electron transport layer and the second electron transport layer of the blue light-emitting device is greater than or equal to 70 nm and less than or equal to 170 nm.

[0117] In an exemplary embodiment, the thickness of the second electron transport layer of the blue light-emitting device is greater than or equal to 30 nm and less than or equal to 130 nm. By adjusting the sum of the thicknesses of the first and second electron transport layers of the blue light-emitting device, as well as the thickness of the second electron transport layer of the blue light-emitting device, the optical microcavity of the blue light-emitting device can produce a strong resonance with the blue light, thereby improving the light output intensity of the blue light-emitting device.

[0118] An embodiment of the present invention provides a display device, including the display substrate as described above.

[0119] The display device provided in the embodiment of the present invention can be: a QLED display, a mobile phone, a tablet computer, a television, a monitor, a laptop computer, a digital photo frame, a navigator, or any other product or component with a display function, but the embodiment of the present invention is not limited thereto.

[0120] Although the embodiments of the present invention have been shown and described above, it can be understood that the above embodiments are illustrative and cannot be understood as limitations on the present invention. Ordinary technicians in this field can change, modify, replace and modify the above embodiments within the scope of the present invention.

Claims

1. A quantum dot light-emitting diode, characterized in that: include: a first electrode, a second electrode, and a quantum dot light-emitting layer, a first electron transport layer, and a second electron transport layer disposed between the first electrode and the second electrode, wherein the first electron transport layer and the second electron transport layer are sequentially disposed on a side of the quantum dot light-emitting layer close to the second electrode; In which, the materials of the first electron transport layer and the second electron transport layer include inorganic nanoparticles, the conduction band bottom energy level of the first electron transport layer matches the conduction band bottom energy level of the quantum dot light-emitting layer, the conduction band bottom energy level of the second electron transport layer is greater than the work function of the second electrode and less than the conduction band bottom energy level of the first electron transport layer; the carrier mobility of the second electron transport layer is greater than the carrier mobility of the first electron transport layer, and the second electron transport layer is configured to adjust the length of the optical microcavity between the first electrode and the second electrode.

2. The quantum dot light-emitting diode according to claim 1, wherein The material of the second electron transport layer includes N-type doped zinc oxide nanoparticles.

3. The quantum dot light-emitting diode according to claim 1, wherein The conduction band bottom energy level of the first electron transport layer matches the conduction band bottom energy level of the quantum dot light-emitting layer, including: The difference between the conduction band bottom energy level of the first electron transport layer and the conduction band bottom energy level of the quantum dot light-emitting layer is less than or equal to 0.5 eV.

4. The quantum dot light-emitting diode according to claim 1, wherein The sum of the thicknesses of the first electron transport layer and the second electron transport layer is greater than or equal to 70 nm and less than or equal to 190 nm; the thickness of the first electron transport layer is the distance between the opposite side surfaces of the first electron transport layer close to the first electrode and away from the first electrode, and the thickness of the second electron transport layer is the distance between the opposite side surfaces of the second electron transport layer close to the first electrode and away from the first electrode.

5. The quantum dot light-emitting diode according to claim 4, wherein: The thickness of the second electron transport layer is greater than or equal to 30 nm and less than or equal to 120 nm.

6. The quantum dot light-emitting diode according to claim 1, wherein It also includes an insertion layer arranged between the first electron transport layer and the second electron transport layer, the conduction band bottom energy level of the insertion layer is greater than the conduction band bottom energy level of the first electron transport layer, and the carrier mobility of the insertion layer is less than the carrier mobility of the second electron transport layer.

7. The quantum dot light-emitting diode according to claim 1, wherein: It also includes a covering layer arranged on a side of the second electrode away from the quantum dot light-emitting layer.

8. The quantum dot light-emitting diode according to claim 1, wherein: One of the first electrode and the second electrode is a transmissive electrode, and the other is a reflective electrode.

9. A display substrate, characterized in that: The device comprises a plurality of light-emitting devices, at least one of which comprises a quantum dot light-emitting diode according to any one of claims 1 to 8.

10. The display substrate according to claim 9, wherein: The plurality of light-emitting devices include a red light-emitting device, and a sum of thicknesses of a first electron transport layer and a second electron transport layer of the red light-emitting device is greater than or equal to 100 nm and less than or equal to 190 nm.

11. The display substrate according to claim 10, wherein: The thickness of the second electron transport layer of the red light-emitting device is greater than or equal to 60 nm and less than or equal to 150 nm.

12. The display substrate according to claim 9, wherein: The plurality of light-emitting devices include a green light-emitting device, and the sum of the thicknesses of the first electron transport layer and the second electron transport layer of the green light-emitting device is greater than or equal to 80 nm and less than or equal to 180 nm.

13. The display substrate according to claim 12, wherein: The thickness of the second electron transport layer of the green light-emitting device is greater than or equal to 40 nm and less than or equal to 140 nm.

14. The display substrate according to claim 9, wherein: The plurality of light-emitting devices include a blue light-emitting device, and the sum of the thicknesses of the first electron transport layer and the second electron transport layer of the blue light-emitting device is greater than or equal to 70 nm and less than or equal to 170 nm.

15. The display substrate according to claim 14, wherein: The thickness of the second electron transport layer of the blue light-emitting device is greater than or equal to 30 nm and less than or equal to 130 nm.

16. A display device, characterized in that: The display substrate comprises the display substrate as claimed in any one of claims 9 to 15.

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