Display panel, preparation method thereof and display device

Abstract

Embodiments of the present application provide a display panel, a preparation method thereof and a display device. The display panel comprises a substrate and a first color quantum dot light-emitting device on the substrate. The first color quantum dot light-emitting device is an inverted light-emitting device. The first color quantum dot light-emitting device comprises a first cathode, a first quantum dot light-emitting layer, at least two hole transport layers and a first anode which are stacked. The first cathode is located on the side of the first anode close to the substrate. In the thickness direction of the display panel, the ith hole transport layer in the first color quantum dot light-emitting device is located between the (i+1)th hole transport layer and the first quantum dot light-emitting layer. The valence band of the material of the first quantum dot light-emitting layer is lower than the HOMO energy level of the material of the ith hole transport layer, and the HOMO energy level of the material of the ith hole transport layer is lower than the HOMO energy level of the material of the (i+1)th hole transport layer. i is a positive integer. Embodiments of the present application can improve the light-emitting efficiency and working life of the quantum dot light-emitting device.

Description

Technical Field

[0001] This application belongs to the field of display technology, and in particular relates to a display panel, its manufacturing method, and a display device. Background Technology

[0002] Due to the characteristics of quantum dots (QDs) such as adjustable size of light emission, narrow half-peak width, high photoluminescence efficiency and thermal stability, quantum dot light-emitting diodes (QLEDs) with quantum dots as the light-emitting center have become a very promising next-generation light-emitting device.

[0003] However, the inventors of this application have found that the number of positive and negative charge carriers in the light-emitting layer of current QLED devices varies greatly, resulting in low luminous efficiency and low operating life of QLED devices. Summary of the Invention

[0004] This application provides a display panel and its manufacturing method, as well as a display device, which can solve the technical problems of low luminous efficiency and low lifespan of QLED devices.

[0005] In a first aspect, embodiments of this application provide a display panel, the display panel including a substrate and a first color quantum dot light-emitting device located on the substrate, the first color quantum dot light-emitting device being an inverted light-emitting device; the first color quantum dot light-emitting device including a first cathode, a first quantum dot light-emitting layer, at least two hole transport layers and a first anode stacked thereon, the first cathode being located on the side of the first anode closer to the substrate; along the thickness direction of the display panel, the i-th hole transport layer in the first color quantum dot light-emitting device is located between the (i+1)-th hole transport layer and the first quantum dot light-emitting layer, the valence band of the material of the first quantum dot light-emitting layer is lower than the highest occupied molecular orbital (HOMO) energy level of the material of the i-th hole transport layer, the HOMO energy level of the material of the i-th hole transport layer is lower than the HOMO energy level of the material of the (i+1)-th hole transport layer, where i is a positive integer.

[0006] According to an embodiment of the first aspect of this application, the display panel further includes a second color quantum dot light-emitting device located on a substrate. The second color quantum dot light-emitting device is a positively positioned light-emitting device. The second color quantum dot light-emitting device includes a second anode, a first hole transport layer, a second quantum dot light-emitting layer, and a second cathode stacked together. The second anode is located on the side of the second cathode closer to the substrate.

[0007] According to any of the foregoing embodiments of the first aspect of this application, the valence band of the material of the first quantum dot light-emitting layer is smaller than the valence band of the material of the second quantum dot light-emitting layer.

[0008] In this way, for second-color quantum dot light-emitting devices with a large valence band in the second quantum dot light-emitting layer, an upright light-emitting device can be used, with only one hole transport layer (i.e., the first hole transport layer) set up. This avoids the number of holes in the second quantum dot light-emitting layer from significantly exceeding the number of electrons, thus better ensuring the balance between the number of holes and electrons in the second quantum dot light-emitting layer, thereby improving the luminous efficiency and working life of the second-color quantum dot light-emitting device.

[0009] According to any of the foregoing embodiments of the first aspect of this application, the display panel further includes a third color quantum dot light-emitting device located on the substrate, the third color quantum dot light-emitting device being an inverted light-emitting device; the third color quantum dot light-emitting device includes a third cathode, a third quantum dot light-emitting layer, at least two hole transport layers and a third anode stacked together, the third cathode being located on the side of the third anode closer to the substrate; along the thickness direction of the display panel, the j-th hole transport layer in the third color quantum dot light-emitting device is located between the (j+1)-th hole transport layer and the third quantum dot light-emitting layer, the valence band of the material of the third quantum dot light-emitting layer is smaller than the HOMO energy level of the material of the j-th hole transport layer, the HOMO energy level of the material of the j-th hole transport layer is smaller than the HOMO energy level of the material of the (j+1)-th hole transport layer, where j is a positive integer.

[0010] According to any of the foregoing embodiments of the first aspect of this application, the valence band of the material of the third quantum dot light-emitting layer is smaller than the valence band of the material of the second quantum dot light-emitting layer.

[0011] In this way, for third-color quantum dot light-emitting devices with a smaller valence band in the third quantum dot light-emitting layer, at least two hole transport layers can still be set up, and the HOMO energy level of the material of the (j+1)th hole transport layer is greater than the HOMO energy level of the material of the jth hole transport layer, which is greater than the valence band of the material of the third quantum dot light-emitting layer. By matching the energy levels, holes from at least two hole transport layers can be injected into the third quantum dot light-emitting layer in a stepped manner, thereby increasing the number of holes injected into the third quantum dot light-emitting layer, reducing the difference between the number of holes and the number of electrons in the third quantum dot light-emitting layer, and thus improving the luminous efficiency and working life of the third-color quantum dot light-emitting device.

[0012] According to any of the foregoing embodiments of the first aspect of this application, the lowest unoccupied molecular orbital (LUMO) energy level of the material of the i-th hole transport layer in the first color quantum dot light-emitting device is greater than the conduction band of the material of the first quantum dot light-emitting layer; and / or, the LUMO energy level of the material of the j-th hole transport layer in the third color quantum dot light-emitting device is greater than the conduction band of the material of the third quantum dot light-emitting layer.

[0013] In this way, because the LUMO energy level of the material in the i-th hole transport layer of the first-color quantum dot light-emitting device is greater than the conduction band of the first quantum dot light-emitting layer, electrons in the first quantum dot light-emitting layer can be effectively blocked from entering the i-th hole transport layer. This effectively prevents the material of the i-th hole transport layer from deteriorating due to excessive electrons entering the i-th hole transport layer, thus improving the lifetime of the i-th hole transport layer material. Similarly, because the LUMO energy level of the material in the j-th hole transport layer of the third-color quantum dot light-emitting device is greater than the conduction band of the third quantum dot light-emitting layer, electrons in the third quantum dot light-emitting layer can be effectively blocked from entering the j-th hole transport layer. This effectively prevents the material of the j-th hole transport layer from deteriorating due to excessive electrons entering the j-th hole transport layer, thus improving the lifetime of the j-th hole transport layer material.

[0014] According to any of the foregoing embodiments of the first aspect of this application, the LUMO energy level of the material of the (i+1)th hole transport layer in the first color quantum dot light-emitting device is greater than the LUMO energy level of the material of the ith hole transport layer in the first color quantum dot light-emitting device, and / or, the LUMO energy level of the material of the (j+1)th hole transport layer in the third color quantum dot light-emitting device is greater than the LUMO energy level of the material of the jth hole transport layer in the third color quantum dot light-emitting device.

[0015] In this way, since the LUMO energy level of the (i+1)th hole transport layer material in the first-color quantum dot light-emitting device is greater than that of the LUMO energy level of the ith hole transport layer material, it can further effectively block electrons from entering the (i+1)th hole transport layer, effectively preventing electrons from degrading the material of the (i+1)th hole transport layer and improving its lifetime. Similarly, since the LUMO energy level of the (j+1)th hole transport layer material in the third-color quantum dot light-emitting device is greater than that of the jth hole transport layer material, it can further effectively block electrons from entering the (j+1)th hole transport layer, effectively preventing electrons from degrading the material of the (j+1)th hole transport layer and improving its lifetime.

[0016] According to any of the foregoing embodiments of the first aspect of this application, the display panel includes a first pixel circuit, a second pixel circuit, and a third pixel circuit. The first pixel circuit is electrically connected to a first color quantum dot light-emitting device and is used to drive the first color quantum dot light-emitting device to emit light. The second pixel circuit is electrically connected to a second color quantum dot light-emitting device and is used to drive the second color quantum dot light-emitting device to emit light. The third pixel circuit is electrically connected to a third color quantum dot light-emitting device and is used to drive the third color quantum dot light-emitting device to emit light. The first pixel circuit includes a first N-type transistor, the gate of which is electrically connected to a first target node, and the source of which is connected to a ground terminal or a negative terminal. The voltage signal terminal is electrically connected, the drain of the first N-type transistor is electrically connected to the first cathode, and the first anode is electrically connected to the positive voltage signal terminal; the second pixel circuit includes a second N-type transistor, the gate of the second N-type transistor is electrically connected to the second target node, the source of the second N-type transistor is electrically connected to the ground terminal or the negative voltage signal terminal, the drain of the second N-type transistor is electrically connected to the second cathode, and the second anode is electrically connected to the positive voltage signal terminal; the third pixel circuit includes a third N-type transistor, the gate of the third N-type transistor is electrically connected to the third target node, the source of the third N-type transistor is electrically connected to the ground terminal or the negative voltage signal terminal, the drain of the third N-type transistor is electrically connected to the third cathode, and the second anode is electrically connected to the positive voltage signal terminal.

[0017] In this way, the first cathode of the first color quantum dot light-emitting device is electrically connected to the drain of the first N-type transistor, the second cathode of the second color quantum dot light-emitting device is electrically connected to the drain of the second N-type transistor, and the third cathode of the third color quantum dot light-emitting device is electrically connected to the drain of the third N-type transistor. This makes the gate-source voltage Vgs of the first N-type transistor no longer affected by the voltage across the first color quantum dot light-emitting device, the gate-source voltage Vgs of the second N-type transistor no longer affected by the voltage across the second color quantum dot light-emitting device, and the gate-source voltage Vgs of the third N-type transistor no longer affected by the voltage across the third color quantum dot light-emitting device. This effectively reduces the impact of the voltage across the QLED device on the stability and uniformity of the display panel brightness, thereby improving the stability and uniformity of the display panel brightness.

[0018] According to any of the foregoing embodiments of the first aspect of this application, the display panel further includes a driving device layer. Along the thickness direction of the display panel, the driving device layer is located between the substrate and the quantum dot light-emitting device. The quantum dot light-emitting device includes a first color quantum dot light-emitting device, a second color quantum dot light-emitting device, and a third color quantum dot light-emitting device. The second quantum dot light-emitting layer is located in the pixel opening. The second cathode includes a first body portion that overlaps with the pixel opening along the thickness direction of the display panel and an extension portion that does not overlap with the pixel opening along the thickness direction of the display panel. Along the thickness direction of the display panel, the orthographic projection of the extension portion on the substrate overlaps with the orthographic projection of the second N-type transistor on the substrate. The extension portion is electrically connected to the drain of the second N-type transistor through a first via formed in the driving device layer.

[0019] In this way, by making the area of ​​the second cathode larger than the area of ​​the pixel opening, that is, the second cathode includes a first body portion that overlaps with the pixel opening along the thickness direction of the display panel and an extension portion that does not overlap with the pixel opening along the thickness direction of the display panel, the second cathode is electrically connected to the drain of the second N-type transistor through the extension portion. This makes the gate-source voltage Vgs of the second N-type transistor no longer affected by the cross voltage of the second color quantum dot light-emitting device, effectively reducing the impact of the cross voltage of the QLED device on the stability and uniformity of the display panel brightness, and improving the stability and uniformity of the display panel brightness.

[0020] According to any of the foregoing embodiments of the first aspect of this application, along the thickness direction of the display panel, the orthographic projection of the first cathode on the substrate overlaps with the orthographic projection of the first N-type transistor on the substrate, and the first cathode is electrically connected to the drain of the first N-type transistor through a second via formed on the driving device layer.

[0021] According to any of the foregoing embodiments of the first aspect of this application, along the thickness direction of the display panel, the orthographic projection of the third cathode on the substrate overlaps with the orthographic projection of the third N-type transistor on the substrate, and the third cathode is electrically connected to the drain of the third N-type transistor through a third via formed on the driving device layer.

[0022] According to any of the foregoing embodiments of the first aspect of this application, the first anode and the third anode are electrically connected, and are electrically connected to the second anode through the first overlap portion.

[0023] In this way, the first anode, the second anode, and the third anode are electrically connected, which makes the anode voltage of the first color quantum dot light-emitting device, the second color quantum dot light-emitting device, and the third color quantum dot light-emitting device consistent, making it easier to control the brightness of each color quantum dot light-emitting device in the display panel.

[0024] According to any of the foregoing embodiments of the first aspect of this application, the thickness of the second anode is greater than or equal to 30 nm and less than or equal to 500 nm.

[0025] In this way, by increasing the thickness of the second anode to over 30 nm, i.e., increasing the cross-sectional area of ​​the second anode, the IR-drop of the second anode can be reduced. When the second anode is electrically connected to the first and third anodes, the overall IR-drop of the first, second, and third anodes can be reduced.

[0026] According to any of the foregoing embodiments of the first aspect of this application, the thickness of each hole transport layer is greater than or equal to 50 angstroms and less than or equal to 2000 angstroms.

[0027] Since the hole injection capability of the hole transport layer is related to the thickness of the hole transport layer, increasing the thickness of the hole transport layer to more than 50 angstroms can increase the hole injection capability of the hole transport layer, that is, increase the number of holes injected into the first quantum dot light-emitting layer, thereby further reducing the difference between the number of holes and the number of electrons in the first quantum dot light-emitting layer, and thus improving the luminous efficiency and working life of the first color quantum dot light-emitting device and the display panel.

[0028] According to any of the foregoing embodiments of the first aspect of this application, the first anode and the third anode are both located in the same anode layer, and the first anode and the third anode are electrically connected to form a planar electrode, and a hollow portion is provided in the planar electrode; along the thickness direction of the display panel, the hollow portion overlaps with the second color quantum dot light-emitting device.

[0029] In this way, on the one hand, since the first anode and the third anode are electrically connected as planar electrodes, the IR-drop of the first anode and the third anode can be reduced; on the other hand, by setting a hollow part in the area overlapping with the second color quantum dot light-emitting device, crosstalk between the first anode and the third anode and the second color quantum dot light-emitting device can be effectively avoided, ensuring the normal light emission of the second color quantum dot light-emitting device.

[0030] According to any of the foregoing embodiments of the first aspect of this application, both the first color quantum dot light-emitting device and the third color quantum dot light-emitting device include a second hole transport layer and a third hole transport layer. Along the thickness direction of the display panel, the second hole transport layer is located between the third hole transport layer and the first and third quantum dot light-emitting layers. The valence bands of the materials of the first and third quantum dot light-emitting layers are both smaller than the HOMO energy level of the material of the second hole transport layer, and the HOMO energy level of the material of the second hole transport layer is smaller than the HOMO energy level of the material of the third hole transport layer.

[0031] In this way, since both the first-color quantum dot light-emitting device and the third-color quantum dot light-emitting device include a second hole transport layer and a third hole transport layer, and the HOMO energy level of the material of the third hole transport layer is greater than the HOMO energy level of the material of the second hole transport layer, which is greater than the valence band of the materials of the first and third quantum dot light-emitting layers, the holes in the third and second hole transport layers can be injected into the first and third quantum dot light-emitting layers in a stepped manner through energy level matching. This increases the number of holes injected into the first and third quantum dot light-emitting layers, reduces the difference between the number of holes and the number of electrons in the first and third quantum dot light-emitting layers, and thus improves the luminous efficiency and working life of the first-color quantum dot light-emitting device and the third-color quantum dot light-emitting device.

[0032] According to any of the foregoing embodiments of the first aspect of this application, the first cathode, the second cathode, and the third cathode are disposed in the same layer.

[0033] In this way, since the first cathode, the second cathode, and the third cathode are set in the same layer, that is, the first cathode, the second cathode, and the third cathode are prepared by the same process, the number of film layers in the display panel can be reduced, which is conducive to simplifying the production process and reducing production costs.

[0034] Secondly, embodiments of this application provide a method for fabricating a display panel. The method includes: providing a substrate; sequentially forming a first cathode, a first quantum dot light-emitting layer, at least two hole transport layers, and a first anode in a plurality of first regions on a first side of the substrate to obtain a first color quantum dot light-emitting device; along the thickness direction of the display panel, the i-th hole transport layer in the first color quantum dot light-emitting device is located between the (i+1)-th hole transport layer and the first quantum dot light-emitting layer, wherein the valence band of the material of the first quantum dot light-emitting layer is smaller than the HOMO energy level of the material of the i-th hole transport layer, and the HOMO energy level of the material of the i-th hole transport layer is smaller than the HOMO energy level of the material of the (i+1)-th hole transport layer, where i is a positive integer.

[0035] Thirdly, embodiments of this application provide a display device, which includes a display panel as provided in the first aspect.

[0036] The display panel and its fabrication method and display device of the present application embodiment include a substrate and a first color quantum dot light-emitting device located on the substrate. The first color quantum dot light-emitting device is an inverted light-emitting device. The first color quantum dot light-emitting device includes a first cathode, a first quantum dot light-emitting layer, at least two hole transport layers and a first anode stacked together. The first cathode is located on the side of the first anode close to the substrate. Along the thickness direction of the display panel, the i-th hole transport layer in the first color quantum dot light-emitting device is located between the (i+1)-th hole transport layer and the first quantum dot light-emitting layer. The valence band of the material of the first quantum dot light-emitting layer is lower than the highest occupied molecular orbital (HOMO) energy level of the material of the i-th hole transport layer. The HOMO energy level of the material of the i-th hole transport layer is lower than the HOMO energy level of the material of the (i+1)-th hole transport layer. i is a positive integer. Since the first color quantum dot light-emitting device includes at least two hole transport layers, and the HOMO energy level of the material of the (i+1)th hole transport layer is greater than the HOMO energy level of the material of the ith hole transport layer, which is greater than the valence band of the material of the first quantum dot light-emitting layer, the holes in the at least two hole transport layers can be injected into the first quantum dot light-emitting layer in a stepped manner through energy level matching. This increases the number of holes injected into the first quantum dot light-emitting layer, reduces the difference between the number of holes and the number of electrons in the first quantum dot light-emitting layer, and thus improves the luminous efficiency and working life of the first color quantum dot light-emitting device and the display panel. Attached Figure Description

[0037] To more clearly illustrate the technical solutions of the embodiments of this application, the accompanying drawings used in the embodiments of this application will be briefly introduced below. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0038] Figure 1 This is a schematic diagram of the energy levels of a quantum dot light-emitting diode.

[0039] Figure 2 This is a cross-sectional schematic diagram of a display panel provided in an embodiment of this application;

[0040] Figure 3 This is a schematic diagram of the energy levels of the i-th hole transport layer and the (i+1)-th hole transport layer;

[0041] Figure 4 Another cross-sectional view of the display panel provided in an embodiment of this application;

[0042] Figure 5 A schematic diagram of the energy levels of quantum dot materials of various colors;

[0043] Figure 6 Another cross-sectional view of the display panel provided in an embodiment of this application;

[0044] Figure 7 Another cross-sectional schematic diagram of the display panel provided in the embodiments of this application;

[0045] Figure 8 A circuit diagram of a quantum dot light-emitting diode;

[0046] Figure 9 Another circuit diagram of the display panel provided in the embodiments of this application;

[0047] Figure 10 Another cross-sectional schematic diagram of the display panel provided in the embodiments of this application;

[0048] Figure 11 Another cross-sectional schematic diagram of the display panel provided in the embodiments of this application;

[0049] Figure 12 A top view schematic diagram of a display panel provided in an embodiment of this application;

[0050] Figure 13 Another cross-sectional schematic diagram of the display panel provided in the embodiments of this application;

[0051] Figure 14 A schematic diagram of the chemical structure of a material for the second hole transport layer in a display panel provided in an embodiment of this application;

[0052] Figure 15 A schematic diagram of the chemical structure of a material for the third hole transport layer in a display panel provided in an embodiment of this application;

[0053] Figure 16 A schematic flowchart illustrating a method for manufacturing a display panel according to an embodiment of this application;

[0054] Figure 17 This is another schematic flowchart illustrating a method for manufacturing a display panel according to an embodiment of this application.

[0055] Figure 18 This is another schematic flowchart illustrating a method for manufacturing a display panel according to an embodiment of this application.

[0056] Figure 19 This is a schematic diagram of a display device provided in an embodiment of this application. Detailed Implementation

[0057] The features and exemplary embodiments of various aspects of this application will be described in detail below. To make the objectives, technical solutions, and advantages of this application clearer, the application will be further described in detail below with reference to the accompanying drawings and specific embodiments. It should be understood that the specific embodiments described herein are only intended to explain this application and not to limit it. For those skilled in the art, this application can be implemented without some of these specific details. The following description of the embodiments is merely to provide a better understanding of this application by illustrating examples.

[0058] It should be noted that, in this document, relational terms such as "first" and "second" are used merely to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitations, an element defined by the phrase "comprising..." does not exclude the presence of additional identical elements in the process, method, article, or apparatus that includes said element.

[0059] It should be understood that the term "and / or" used in this article is merely a description of the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent: A existing alone, A and B existing simultaneously, and B existing alone. Additionally, the character " / " in this article generally indicates that the preceding and following related objects have an "or" relationship.

[0060] It should be noted that the transistors in this embodiment are described using an N-type transistor as an example, but are not limited to N-type transistors; they can also be replaced with P-type transistors. For an N-type transistor, the on-state is high and the off-state is low. That is, when the gate of an N-type transistor is high, its first and second terminals are connected; when the gate of an N-type transistor is low, its first and second terminals are off. For a P-type transistor, the on-state is low and the off-state is high. That is, when the control terminal of a P-type transistor is low, its first and second terminals are connected; when the control terminal of a P-type transistor is high, its first and second terminals are off. In specific implementation, the gate of each transistor is used as its control electrode. Furthermore, depending on the signal and type of the gate of each transistor, its first electrode can be used as the source and its second electrode as the drain, or its first electrode can be used as the drain and its second electrode as the source. No distinction is made here. In addition, the on-level and off-level in the embodiments of the present invention are general terms. The on-level refers to any level that can turn on the transistor, and the off-level refers to any level that can turn off / turn off the transistor.

[0061] In the embodiments of this application, the term "electrical connection" can refer to a direct electrical connection between two components, or it can refer to an electrical connection between two components via one or more other components.

[0062] In the embodiments of this application, the first target node, the second target node, and the third target node are defined only for the convenience of describing the circuit structure, and the first target node, the second target node, and the third target node are not actual circuit units.

[0063] Various modifications and variations can be made to this application without departing from its spirit or scope, which will be apparent to those skilled in the art. Therefore, this application is intended to cover modifications and variations falling within the scope of the corresponding claims (the claimed technical solutions) and their equivalents. It should be noted that the embodiments provided in this application can be combined with each other without contradiction.

[0064] Before describing the technical solutions provided in the embodiments of this application, in order to facilitate understanding of the embodiments of this application, this application first specifically explains the problems existing in the prior art:

[0065] Quantum dot light-emitting diodes (QLEDs) possess advantages such as high color gamut, long potential lifetime, good viewing angle, and low cost, making them highly promising next-generation light-emitting devices. However, the inventors of this application have discovered that the number of positive and negative charge carriers in the light-emitting layer of current QLED devices differs significantly, leading to lower luminous efficiency and operating lifetime.

[0066] Figure 1This is a schematic diagram of the energy levels of a quantum dot light-emitting diode. Specifically, as shown... Figure 1 As shown, a quantum dot light-emitting diode (LED) may include a hole transport layer 11, a quantum dot light-emitting layer 12, and an electron transport layer 13. The hole transport layer 11 can be electrically connected to the anode of the quantum dot LED, and the electron transport layer 13 can be electrically connected to the cathode of the quantum dot LED. Under the influence of energy level matching and an applied electric field, electrons e in the cathode and electron transport layer 13 can migrate to the quantum dot light-emitting layer 12, and holes h in the anode and hole transport layer 11 can migrate to the quantum dot light-emitting layer 12. When electrons e and holes h meet in the quantum dot light-emitting layer 12, excitons are generated. The energy of the excitons decays in the form of light, i.e., light is emitted.

[0067] The hole transport layer 11 can be made of organic materials, such as poly[(N,N'-(4-n-butylphenyl)-N,N'-diphenyl-1,4-phenylenediamine)-ALT-(9,9-di-n-octylfluorenyl-2,7-diyl)], abbreviated as TFB. The quantum dot emitting layer 12 can be made of quantum dot materials. The electron transport layer 13 can be made of inorganic materials, such as zinc oxide (ZnO). The inventors of this application have discovered that because inorganic materials such as ZnO have a deeper conduction band (i.e., the difference between the conduction band of inorganic materials such as ZnO and the conduction band of quantum dot materials is small), it is conducive to the injection of electrons (e). However, the valence band of quantum dot materials is deeper (i.e., the difference between the valence band of quantum dot materials and the HOMO energy level of the hole transport layer 11 is large). Therefore, it is difficult for holes (h) from the hole transport layer 11 to be injected into the quantum dot light-emitting layer 12. As a result, there are more electrons and fewer holes in the quantum dot light-emitting layer 12. The number of electrons and holes in the quantum dot light-emitting layer 12 is unbalanced, which in turn leads to a lower luminous efficiency and working life of the quantum dot light-emitting diode.

[0068] In view of the inventors’ above-mentioned research findings, the embodiments of this application provide a display panel and its preparation method and display device, which can solve the technical problems of low luminous efficiency and low working life of quantum dot light-emitting diodes in related technologies.

[0069] The technical concept of this application embodiment lies in: setting the first color quantum dot light-emitting device in the display panel as an inverted light-emitting device, so that the first color quantum dot light-emitting device can have at least two hole transport layers. By matching the energy levels of the at least two hole transport layers, holes in the at least two hole transport layers can be injected into the first quantum dot light-emitting layer of the first color quantum dot light-emitting device in a stepped manner, thereby increasing the number of holes injected into the first quantum dot light-emitting layer, reducing the difference between the number of holes and the number of electrons in the first quantum dot light-emitting layer, and thus improving the luminous efficiency and working life of the first color quantum dot light-emitting device and the display panel.

[0070] The display panel provided in the embodiments of this application will be described first below.

[0071] Figure 2 This is a cross-sectional schematic diagram of a display panel provided in an embodiment of this application. Figure 2 As shown, the display panel includes a substrate 01 and a first-color quantum dot light-emitting device 20 located on the substrate 01. Exemplarily, the substrate 01 may include a commonly used rigid substrate such as glass or metal foil, or a flexible substrate such as polyimide (PI), polycarbonate (PC), polystyrene (PS), polyethylene (PE), polyvinyl chloride (PV), polyvinylpyrrolidone (PVP), polyethylene terephthalate (PET), or similar materials, primarily serving a supporting function. Exemplarily, the first-color quantum dot light-emitting device 20 may include a blue quantum dot light-emitting device or a green quantum dot light-emitting device. Of course, in some examples, the first-color quantum dot light-emitting device 20 may also be a red quantum dot light-emitting device; this embodiment of the application does not limit this.

[0072] In this embodiment, the first color quantum dot light-emitting device 20 can be an inverted light-emitting device. For an inverted light-emitting device, its cathode is closer to the substrate 01 than its anode. Specifically, the first color quantum dot light-emitting device 20 may include a first cathode 201, a first quantum dot light-emitting layer 202, at least two hole transport layers 203, and a first anode 204 stacked together, with the first cathode 201 located on the side of the first anode 204 closer to the substrate 01.

[0073] The reason why the first color quantum dot light-emitting device 20 is set as an inverted light-emitting device in this embodiment is mainly because:

[0074] The inventors of this application have discovered that, for upright light-emitting devices, the hole transport layer 203 is located below the first quantum dot light-emitting layer 202 (i.e., on the side closer to the substrate 01). Therefore, when fabricating the first color quantum dot light-emitting device 20, the hole transport layer 203 is fabricated first, followed by the first quantum dot light-emitting layer 202. If the hole transport layer 203 is fabricated using a vapor deposition process, the small organic molecules formed by the vapor deposition process are relatively small, making it easy for the hole transport layer 203 to be eroded during the subsequent fabrication of the first quantum dot light-emitting layer 202. Therefore, for upright light-emitting devices, the hole transport layer 203 can generally only be formed using an ink printing process. However, the ink printing process cannot effectively form multiple stacked hole transport layers 203. Therefore, for upright light-emitting devices, typically only one hole transport layer 203 can be provided.

[0075] However, for inverted light-emitting devices, the hole transport layer 203 is located above the first quantum dot light-emitting layer 202 (i.e., on the side away from the substrate 01). Therefore, when fabricating the first color quantum dot light-emitting device 20, the first quantum dot light-emitting layer 202 is fabricated first, followed by the hole transport layer 203. Since the first quantum dot light-emitting layer 202 is already formed when the hole transport layer 203 is fabricated, the hole transport layer 203 can be fabricated using a vapor deposition process. This vapor deposition process can effectively form multiple stacked hole transport layers 203. Therefore, for inverted light-emitting devices, multiple hole transport layers 203 can be formed.

[0076] See also Figure 2 Along the thickness direction Z of the display panel, the i-th hole transport layer 203 in the first color quantum dot light-emitting device 20 is located between the (i+1)-th hole transport layer 203 and the first quantum dot light-emitting layer 202. That is, compared to the i-th hole transport layer 203, the (i+1)-th hole transport layer 203 is further away from the first quantum dot light-emitting layer 202.

[0077] Figure 3 This is a schematic diagram of the energy levels of the i-th hole transport layer and the (i+1)-th hole transport layer. (Combined with...) Figure 2 and Figure 3 As shown, the valence band of the material of the first quantum dot light-emitting layer 202 is smaller than the highest occupied molecular orbital (HOMO) energy level of the material of the i-th hole transport layer 203, and the HOMO energy level of the material of the i-th hole transport layer 203 is smaller than the HOMO energy level of the material of the (i+1)-th hole transport layer 203, where i is a positive integer.

[0078] It should be noted that organic materials possess both the Highest Occupied Molecular Orbital (HOMO) and Lowest Unoccupied Molecular Orbital (LUMO) energy levels. The HOMO energy levels of organic materials are similar to the valence band of inorganic materials, while the LUMO energy levels are similar to the conduction band of inorganic materials. For quantum dot materials, the valence band can also be referred to as the HOMO energy level, and the conduction band can also be referred to as the LUMO energy level.

[0079] Since the HOMO energy level of the material of the i-th hole transport layer 203 is lower than that of the material of the (i+1)-th hole transport layer 203, holes in the (i+1)-th hole transport layer 203 can migrate to the i-th hole transport layer 203. Since the valence band of the material of the first quantum dot emitting layer 202 is lower than that of the material of the i-th hole transport layer 203, both the original holes in the i-th hole transport layer 203 and the holes migrated from the (i+1)-th hole transport layer 203 to the i-th hole transport layer 203 can migrate to the first quantum dot emitting layer 202. That is, holes are injected into the first quantum dot emitting layer 202 in a stepwise manner, thereby increasing the number of holes injected into the first quantum dot emitting layer.

[0080] In the display panel of this application embodiment, since the first color quantum dot light-emitting device includes at least two hole transport layers, and the HOMO energy level of the material of the (i+1)th hole transport layer is greater than the HOMO energy level of the material of the ith hole transport layer and the valence band of the material of the first quantum dot light-emitting layer, the holes in the at least two hole transport layers can be injected into the first quantum dot light-emitting layer in a stepped manner through energy level matching, thereby increasing the number of holes injected into the first quantum dot light-emitting layer, reducing the difference between the number of holes and the number of electrons in the first quantum dot light-emitting layer, and thus improving the luminous efficiency and working life of the first color quantum dot light-emitting device and the display panel.

[0081] Figure 4 This is another cross-sectional view of the display panel provided in an embodiment of this application. (See diagram below.) Figure 4 As shown, according to some embodiments of this application, optionally, the first color quantum dot light-emitting device 20 may further include a first hole injection layer 205 and a first electron transport layer 206. Along the thickness direction Z of the display panel, the first hole injection layer 205 is located between the hole transport layer 203 and the first anode 204, and the first electron transport layer 206 is located between the first cathode 201 and the first quantum dot light-emitting layer 202.

[0082] In some embodiments, the material of the hole transport layer 203 includes, but is not limited to, at least one of poly(9,9-dioctylfluorene-CO-N-(4-butylphenyl)diphenylamine), polyvinylcarbazole, poly(N,N'-bis(4-butylphenyl)-N,N'-bis(phenyl)benzidine), poly(9,9-dioctylfluorene-co-bis-N,N-phenyl-1,4-phenylenediamine), 4,4',4”-tris(carbazole-9-yl)triphenylamine, 4,4'-bis(9-carbazole)biphenyl, N,N'-diphenyl-N,N'-di(3-methylphenyl)-1,1'-biphenyl-4,4'-diamine, 15N,N'-diphenyl-N,N'-(1-naphthyl)-1,1'-biphenyl-4,4'-diamine, graphene, and C60.

[0083] In some embodiments, the material of the first hole injection layer 205 includes, but is not limited to, at least one of poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS), polythiophene, polyaniline, polypyrrole, and copper phthalocyanine.

[0084] In some embodiments, the material of the first electron transport layer 206 includes, but is not limited to, at least one of ZnO, TiO2, SnO2, Ta2O3, ZrO2, NiO, TiLiO, ZnAlO, ZnMgO, ZnSnO, ZnLiO, and InSnO.

[0085] In some embodiments, the first color quantum dot light-emitting device 20 may further include a first electron injection layer (not shown in the figure), which may be located between the first electron transport layer 206 and the first cathode 201 along the thickness direction Z of the display panel. Exemplarily, the material of the first electron injection layer includes, but is not limited to, at least one of lithium fluoride, sodium fluoride, potassium fluoride, rubidium fluoride, cesium fluoride, lithium oxide, and lithium metaborate.

[0086] Figure 5 This is a schematic diagram of the energy levels of quantum dot materials in various colors. (Example:) Figure 5 As shown, compared to red quantum dot materials, blue and green quantum dot materials have deeper valence bands, meaning the difference between their valence bands and the HOMO energy levels of the hole transport layer is greater. Therefore, it is more difficult for holes in the hole transport layer to be injected into the quantum dot light-emitting layer formed by blue or green quantum dot materials. Consequently, compared to red quantum dot LEDs, blue and green quantum dot LEDs exhibit a greater imbalance in the number of electrons and holes, resulting in more severe issues with lower luminous efficiency and lifespan. In contrast, red quantum dot LEDs suffer from relatively milder problems with lower luminous efficiency and lifespan.

[0087] Therefore, in view of the above research findings, this application considers, for example, for red quantum dot light-emitting diodes, the use of a positive-type light-emitting device, that is, only one hole transport layer, to avoid the number of holes in the quantum dot light-emitting layer of the red quantum dot light-emitting diode significantly exceeding the number of electrons, thereby affecting the luminous efficiency and working life of the red quantum dot light-emitting device.

[0088] Figure 6 This is another cross-sectional view of the display panel provided in an embodiment of this application. (See diagram below.) Figure 6As shown, according to some embodiments of this application, optionally, the display panel may further include a second color quantum dot light-emitting device 30 located on the substrate 01. The second color quantum dot light-emitting device 30 may be a positively positioned light-emitting device. For a positively positioned light-emitting device, its anode is closer to the substrate 01 than its cathode. Specifically, the second color quantum dot light-emitting device 30 may include a second anode 301, a first hole transport layer 302, a second quantum dot light-emitting layer 303, and a second cathode 304 stacked together, with the second anode 301 located on the side of the second cathode 304 closer to the substrate 01. In some examples, the valence band of the material of the first quantum dot light-emitting layer 202 may be smaller than the valence band of the material of the second quantum dot light-emitting layer 303. For example, the first color quantum dot light-emitting device 20 may be a blue quantum dot light-emitting diode or a green quantum dot light-emitting diode, and the second color quantum dot light-emitting device 30 may be a red quantum dot light-emitting diode.

[0089] In this way, for second-color quantum dot light-emitting devices with a large valence band in the second quantum dot light-emitting layer, an upright light-emitting device can be used, with only one hole transport layer (i.e., the first hole transport layer) set up. This avoids the number of holes in the second quantum dot light-emitting layer from significantly exceeding the number of electrons, thus better ensuring the balance between the number of holes and electrons in the second quantum dot light-emitting layer, thereby improving the luminous efficiency and working life of the second-color quantum dot light-emitting device.

[0090] Figure 7 This is yet another cross-sectional view of the display panel provided in an embodiment of this application. For example... Figure 7 As shown, according to some embodiments of this application, optionally, the display panel may further include a third-color quantum dot light-emitting device 40 located on the substrate 01. The third-color quantum dot light-emitting device 40 may be an inverted light-emitting device. For an inverted light-emitting device, its cathode is closer to the substrate 01 than its anode. Specifically, the third-color quantum dot light-emitting device 40 may include a third cathode 401, a third quantum dot light-emitting layer 402, at least two hole transport layers 403, and a third anode 404 stacked together, with the third cathode 401 located on the side of the third anode 404 closer to the substrate 01. Along the thickness direction Z of the display panel, the j-th hole transport layer 403 in the third-color quantum dot light-emitting device 40 may be located between the (j+1)-th hole transport layer 403 and the third quantum dot light-emitting layer 402, where j is a positive integer. That is, the (j+1)-th hole transport layer 403 is further away from the third quantum dot light-emitting layer 402 than the j-th hole transport layer 403.

[0091] Similarly, the valence band of the material of the third quantum dot emitting layer 402 can be lower than the HOMO level of the material of the j-th hole transport layer 403, and the HOMO level of the material of the j-th hole transport layer 403 is lower than the HOMO level of the material of the (j+1)-th hole transport layer 403. Since the HOMO level of the material of the j-th hole transport layer 403 is lower than the HOMO level of the material of the (j+1)-th hole transport layer 403, holes from the (j+1)-th hole transport layer 403 can migrate to the j-th hole transport layer 403. Since the valence band of the material of the third quantum dot emitting layer 402 is smaller than the HOMO energy level of the material of the j-th hole transport layer 403, the original holes in the j-th hole transport layer 403 and the holes that migrated from the (j+1)-th hole transport layer 403 to the j-th hole transport layer 403 can both migrate to the third quantum dot emitting layer 402. That is, the holes are injected into the third quantum dot emitting layer 402 in a stepwise manner, thereby increasing the number of holes injected into the third quantum dot emitting layer.

[0092] In some examples, the valence band of the material of the third quantum dot light-emitting layer 402 can be smaller than that of the material of the second quantum dot light-emitting layer 303. For example, the first color quantum dot light-emitting device 20 can be a blue quantum dot light-emitting diode, the second color quantum dot light-emitting device 30 can be a red quantum dot light-emitting diode, and the third color quantum dot light-emitting device 40 can be a green quantum dot light-emitting diode. As another example, the first color quantum dot light-emitting device 20 can be a green quantum dot light-emitting diode, the second color quantum dot light-emitting device 30 can be a red quantum dot light-emitting diode, and the third color quantum dot light-emitting device 40 can be a blue quantum dot light-emitting diode.

[0093] In this way, for third-color quantum dot light-emitting devices with a smaller valence band in the third quantum dot light-emitting layer, at least two hole transport layers can still be set up, and the HOMO energy level of the material of the (j+1)th hole transport layer is greater than the HOMO energy level of the material of the jth hole transport layer, which is greater than the valence band of the material of the third quantum dot light-emitting layer. By matching the energy levels, holes from at least two hole transport layers can be injected into the third quantum dot light-emitting layer in a stepped manner, thereby increasing the number of holes injected into the third quantum dot light-emitting layer, reducing the difference between the number of holes and the number of electrons in the third quantum dot light-emitting layer, and thus improving the luminous efficiency and working life of the third-color quantum dot light-emitting device.

[0094] Continue to combine Figure 2 and Figure 3 As shown, according to some embodiments of this application, optionally, the LUMO energy level of the material of the i-th hole transport layer 203 in the first color quantum dot light-emitting device 20 can be greater than the conduction band of the material of the first quantum dot light-emitting layer 202.

[0095] In this way, since the LUMO energy level of the material of the i-th hole transport layer in the first color quantum dot light-emitting device is greater than the conduction band of the material of the first quantum dot light-emitting layer, it can effectively block electrons in the first quantum dot light-emitting layer from entering the i-th hole transport layer, effectively avoiding the deterioration of the material of the i-th hole transport layer due to too many electrons entering the i-th hole transport layer, and improving the lifetime of the material of the i-th hole transport layer.

[0096] Similarly, according to some embodiments of this application, optionally, the LUMO energy level of the material of the j-th hole transport layer in the third color quantum dot light-emitting device can be greater than the conduction band of the material of the third quantum dot light-emitting layer.

[0097] In this way, since the LUMO energy level of the material of the j-th hole transport layer in the third color quantum dot light-emitting device is greater than the conduction band of the material of the third quantum dot light-emitting layer, it can effectively block electrons in the third quantum dot light-emitting layer from entering the j-th hole transport layer. This effectively avoids the deterioration of the material of the j-th hole transport layer due to too many electrons entering the j-th hole transport layer, and improves the lifetime of the material of the j-th hole transport layer.

[0098] Continue to combine Figure 2 and Figure 3 As shown, according to some embodiments of this application, optionally, the LUMO energy level of the material of the (i+1)th hole transport layer 203 in the first color quantum dot light-emitting device 20 can be greater than the LUMO energy level of the material of the i-th hole transport layer 203 in the first color quantum dot light-emitting device 20.

[0099] In this way, since the LUMO energy level of the material of the (i+1)th hole transport layer in the first color quantum dot light-emitting device is greater than the LUMO energy level of the material of the ith hole transport layer in the first color quantum dot light-emitting device, it can further effectively block electrons in the ith hole transport layer from entering the (i+1)th hole transport layer, effectively avoiding the degradation of the material of the (i+1)th hole transport layer by electrons and improving the lifetime of the material of the (i+1)th hole transport layer.

[0100] Similarly, according to some embodiments of this application, optionally, the LUMO energy level of the material of the (j+1)th hole transport layer in the third color quantum dot light-emitting device can be greater than the LUMO energy level of the material of the jth hole transport layer in the third color quantum dot light-emitting device.

[0101] In this way, since the LUMO energy level of the material of the (j+1)th hole transport layer in the third-color quantum dot light-emitting device is greater than that of the material of the jth hole transport layer in the third-color quantum dot light-emitting device, it can further effectively block electrons in the LUMO energy level of the material of the jth hole transport layer in the third-color quantum dot light-emitting device from entering the (j+1)th hole transport layer, effectively avoiding the degradation of the material of the (j+1)th hole transport layer by electrons and improving the lifetime of the material of the (j+1)th hole transport layer.

[0102] Figure 8 This is a circuit diagram of a quantum dot light-emitting diode. Figure 8 As shown, the N-type transistor 801 can be electrically connected to the quantum dot light-emitting diode 802, and the N-type transistor 801 can be used to drive the quantum dot light-emitting diode 802 to emit light. Further research by the inventors of this application has revealed that, for example, when the quantum dot light-emitting diode 802 is a positive-position light-emitting device, typically the cathode 8021 of the quantum dot light-emitting diode 802 can be electrically connected to the ground terminal GND, and the anode 8022 of the quantum dot light-emitting diode 802 can be electrically connected to the source of the N-type transistor 801. The gate of the N-type transistor 801 is electrically connected to the first node N1, and the drain of the N-type transistor 801 is electrically connected to the positive voltage signal terminal VDD. When the first node N1 is at a high level, the N-type transistor 801 is turned on, and the quantum dot light-emitting diode 802 emits light. For the N-type transistor 801, the source voltage Vs of the N-type transistor 801 is related to the voltage V at the ground terminal GND. GND The difference between them is V QLED V QLED The voltage across the quantum dot LED 802 is Vs, therefore, Vs = V GND +V QLED Therefore, the gate-source voltage Vgs of the N-type transistor 801 is Vg - (V GND +V QLED Where Vg represents the gate voltage of N-type transistor 801, and Vgs represents the difference between the gate voltage and the source voltage of N-type transistor 801.

[0103] It's easy to understand that the gate-source voltage Vgs affects the current flowing through the N-type transistor 801, thus affecting the brightness of the quantum dot LED 802. However, as the quantum dot LED 802 ages, i.e., as its operating time increases, Vgs... QLED This will change. Therefore, compared to when the quantum dot LED 802 is initially operating, after the quantum dot LED 802 has been operating for a period of time, V... QLEDThis will change, thus altering the gate-source voltage Vgs of the N-type transistor 801. The display panel includes multiple quantum dot light-emitting diodes 802 arranged in an array. As the display panel is used, the operating times of the quantum dot light-emitting diodes 802 in different areas of the display panel are no longer the same, therefore the Vgs of the quantum dot light-emitting diodes 802 in different areas will change. QLED The brightness of the quantum dot LEDs 802 in different areas is no longer the same, which leads to differences in brightness and reduces the stability and uniformity of the display panel.

[0104] In view of the above research findings, this application considers that the cathodes of the first color quantum dot light-emitting device, the second color quantum dot light-emitting device, and the third color quantum dot light-emitting device are all electrically connected to the drain of the N-type transistor, so that the gate-source voltage Vgs of the N-type transistor is no longer affected by the cross voltage of the quantum dot light-emitting device, thereby improving the stability and uniformity of the brightness of the display panel.

[0105] Figure 9 Another circuit diagram of the display panel provided in an embodiment of this application. For example... Figure 9 As shown, according to some embodiments of this application, optionally, the display panel may include a first pixel circuit 91, a second pixel circuit 92, and a third pixel circuit 93. The first pixel circuit 91 may be electrically connected to a first-color quantum dot light-emitting device 20, and the first pixel circuit 91 may be used to drive the first-color quantum dot light-emitting device 20 to emit light. The second pixel circuit 92 may be electrically connected to a second-color quantum dot light-emitting device 30, and the second pixel circuit 92 may be used to drive the second-color quantum dot light-emitting device 30 to emit light. The third pixel circuit 93 is electrically connected to a third-color quantum dot light-emitting device 40, and the third pixel circuit 93 may be used to drive the third-color quantum dot light-emitting device 40 to emit light.

[0106] Specifically, the first pixel circuit 91 may include a first N-type transistor 910. The gate of the first N-type transistor 910 is electrically connected to the first target node N1', the source of the first N-type transistor 910 is electrically connected to the ground terminal GND or the negative voltage signal terminal VSS, the drain of the first N-type transistor 910 is electrically connected to the first cathode 201, and the first anode 204 is electrically connected to the positive voltage signal terminal VDD. When the first target node N1' is at a high potential, the gate-source voltage Vgs of the first N-type transistor 910 is greater than the threshold voltage Vth of the first N-type transistor 910, the first N-type transistor 910 is turned on, and the first color quantum dot light-emitting device 20 emits light. Since the source of the first N-type transistor 910 is electrically connected to the ground terminal GND or the negative voltage signal terminal VSS, taking the connection of the source of the first N-type transistor 910 to the ground terminal GND as an example, the source voltage Vs of the first N-type transistor 910 is V... GND V GNDThis represents the voltage at the ground terminal GND. Therefore, the gate-source voltage Vgs of the first N-type transistor 910 is Vg - V GND That is, the gate-source voltage Vgs of the first N-type transistor is no longer affected by the trans-voltage V of the first color quantum dot light-emitting device. QLED Influence.

[0107] The second pixel circuit 92 may include a second N-type transistor 920. The gate of the second N-type transistor 920 is electrically connected to the second target node N2', the source of the second N-type transistor 920 is electrically connected to the ground terminal GND or the negative voltage signal terminal VSS, the drain of the second N-type transistor 920 is electrically connected to the second cathode 304, and the second anode 301 is electrically connected to the positive voltage signal terminal VDD. When the second target node N2' is at a high potential, the gate-source voltage Vgs of the second N-type transistor 920 is greater than the threshold voltage Vth of the second N-type transistor 920, the second N-type transistor 920 is turned on, and the second color quantum dot light-emitting device 30 emits light. Since the source of the second N-type transistor 920 is electrically connected to the ground terminal GND or the negative voltage signal terminal VSS, taking the source of the second N-type transistor 920 being electrically connected to the ground terminal GND as an example, the source voltage Vs of the second N-type transistor 920 is V... GND V GND This represents the voltage at the ground terminal GND. Therefore, the gate-source voltage Vgs of the second N-type transistor 920 is Vg - V GND That is, the gate-source voltage Vgs of the second N-type transistor is no longer affected by the trans-voltage V of the second color quantum dot light-emitting device. QLED Influence.

[0108] The third pixel circuit 93 may include a third N-type transistor 930. The gate of the third N-type transistor 930 is electrically connected to the third target node N3', the source of the third N-type transistor 930 is electrically connected to the ground terminal GND or the negative voltage signal terminal VSS, the drain of the third N-type transistor 930 is electrically connected to the third cathode 401, and the second anode 404 is electrically connected to the positive voltage signal terminal VDD. When the third target node N3' is at a high potential, the gate-source voltage Vgs of the third N-type transistor 930 is greater than the threshold voltage Vth of the third N-type transistor 930, the third N-type transistor 930 is turned on, and the third color quantum dot light-emitting device 40 emits light. Since the source of the third N-type transistor 930 is electrically connected to the ground terminal GND or the negative voltage signal terminal VSS, taking the connection of the source of the third N-type transistor 930 to the ground terminal GND as an example, the source voltage Vs of the third N-type transistor 930 is V... GND V GND This represents the voltage at the ground terminal GND. Therefore, the gate-source voltage Vgs of the third N-type transistor 930 is Vg - V GND That is, the gate-source voltage Vgs of the third N-type transistor is no longer affected by the trans-voltage V of the third color quantum dot light-emitting device.QLED Influence.

[0109] In this way, the first cathode of the first color quantum dot light-emitting device is electrically connected to the drain of the first N-type transistor, the second cathode of the second color quantum dot light-emitting device is electrically connected to the drain of the second N-type transistor, and the third cathode of the third color quantum dot light-emitting device is electrically connected to the drain of the third N-type transistor. This makes the gate-source voltage Vgs of the first N-type transistor no longer affected by the voltage across the first color quantum dot light-emitting device, the gate-source voltage Vgs of the second N-type transistor no longer affected by the voltage across the second color quantum dot light-emitting device, and the gate-source voltage Vgs of the third N-type transistor no longer affected by the voltage across the third color quantum dot light-emitting device. This effectively reduces the impact of the voltage across the QLED device on the stability and uniformity of the display panel brightness, thereby improving the stability and uniformity of the display panel brightness.

[0110] It should be noted that, functionally, the first N-type transistor 910, the second N-type transistor 920, and the third N-type transistor 930 can be understood as driving transistors, used to provide driving current for quantum dot light-emitting devices.

[0111] Figure 10 This is yet another cross-sectional view of the display panel provided in an embodiment of this application. For example... Figure 10 As shown, according to some embodiments of this application, the display panel may optionally include a driving device layer 02. Along the thickness direction Z of the display panel, the driving device layer 02 may be located between the substrate 01 and the quantum dot light-emitting device 03. The quantum dot light-emitting device 03 may include a first-color quantum dot light-emitting device 20, a second-color quantum dot light-emitting device 30, and a third-color quantum dot light-emitting device 40. A first N-type transistor 910, a second N-type transistor 920, and a third N-type transistor 930 may be located within the driving device layer 02.

[0112] For the second color quantum dot light-emitting device 30, the second quantum dot light-emitting layer 303 can be located within the pixel opening k1. Specifically, the display panel may further include a first pixel definition layer PDL, which is disposed on the same layer as the second quantum dot light-emitting layer 303. The first pixel definition layer PDL has a pixel opening k1, and the second quantum dot light-emitting layer 303 is located within the pixel opening k1. The second cathode 304 may include a first body portion 304a that overlaps with the pixel opening k1 along the thickness direction of the display panel and an extension portion 304b that does not overlap with the pixel opening k1 along the thickness direction of the display panel, that is, the area of ​​the second cathode 304 is larger than the area of ​​the pixel opening k1. Along the thickness direction Z of the display panel, the orthographic projection of the extension portion 304b on the substrate 01 can overlap with the orthographic projection of the second N-type transistor 920 on the substrate 01. The extension portion 304b can be electrically connected to the drain of the second N-type transistor 920 through a first via h1 opened on the driving device layer 02.

[0113] In this way, by making the area of ​​the second cathode larger than the area of ​​the pixel opening, that is, the second cathode includes a first body portion that overlaps with the pixel opening along the thickness direction of the display panel and an extension portion that does not overlap with the pixel opening along the thickness direction of the display panel, the second cathode is electrically connected to the drain of the second N-type transistor through the extension portion. This makes the gate-source voltage Vgs of the second N-type transistor no longer affected by the cross voltage of the second color quantum dot light-emitting device, effectively reducing the impact of the cross voltage of the QLED device on the stability and uniformity of the display panel brightness, and improving the stability and uniformity of the display panel brightness.

[0114] See also Figure 10 According to some embodiments of this application, optionally, for the first color quantum dot light-emitting device 20, along the thickness direction of the display panel, the orthographic projection of the first cathode 201 on the substrate 01 overlaps with the orthographic projection of the first N-type transistor 910 on the substrate 01. The first cathode 201 can be electrically connected to the drain of the first N-type transistor 910 through a second via h2 opened on the driving device layer 02. That is, the first cathode 301 of the first color quantum dot light-emitting device 20 can be directly electrically connected to the drain of the first N-type transistor 910.

[0115] For the third-color quantum dot light-emitting device 40, along the thickness direction of the display panel, the orthographic projection of the third cathode 401 on the substrate 01 overlaps with the orthographic projection of the third N-type transistor 930 on the substrate 01. The third cathode 401 can be electrically connected to the drain of the third N-type transistor 930 through the third via h3 opened on the driving device layer 02. That is, the third cathode 401 of the third-color quantum dot light-emitting device 40 can be directly electrically connected to the drain of the third N-type transistor 930.

[0116] Figure 11This is yet another cross-sectional view of the display panel provided in an embodiment of this application. For example... Figure 11 As shown, according to some embodiments of this application, optionally, the first anode 204 and the third anode 404 are electrically connected. Furthermore, the first anode 204 and the third anode 404 can be electrically connected to the second anode 301 via the first overlap portion 111.

[0117] In this way, the first anode, the second anode, and the third anode are electrically connected, which makes the anode voltage of the first color quantum dot light-emitting device, the second color quantum dot light-emitting device, and the third color quantum dot light-emitting device consistent, making it easier to control the brightness of each color quantum dot light-emitting device in the display panel.

[0118] For the second-color quantum dot light-emitting device 30, since the second anode 301 is located on the side of the second quantum dot light-emitting layer 303 closest to the substrate 01, i.e., on the backlight side of the second quantum dot light-emitting layer 303, the second anode 301 will not block the light emission of the second quantum dot light-emitting layer 303. Therefore, the thickness of the second anode 301 will not affect the transmittance. Thus, the second anode 301 can be set to be relatively thick, for example, its thickness can be greater than or equal to 30 nm and less than or equal to 500 nm. It should be noted that the thickness of the first anode 204 and the third anode 404 can be set to be relatively thin or made of transparent material to avoid affecting light emission.

[0119] In this way, by increasing the thickness of the second anode to over 30 nm, i.e., increasing the cross-sectional area of ​​the second anode, the IR-drop of the second anode can be reduced. When the second anode is electrically connected to the first and third anodes, the overall IR-drop of the first, second, and third anodes can be reduced.

[0120] Research has shown that the hole injection capability of the hole transport layer is related to its thickness. Therefore, increasing the thickness of the hole transport layer can increase its hole injection capability.

[0121] According to some embodiments of this application, optionally, the thickness of each hole transport layer 203 in the first color quantum dot light-emitting device 20 and each hole transport layer 403 in the third color quantum dot light-emitting device 40 can be greater than or equal to 50 angstroms and less than or equal to 2000 angstroms.

[0122] In this way, by increasing the thickness of the hole transport layer to more than 50 angstroms, the hole injection capability of the hole transport layer can be increased, that is, the number of holes injected into the first quantum dot light-emitting layer can be increased, thereby further reducing the difference between the number of holes and the number of electrons in the first quantum dot light-emitting layer, and thus improving the luminous efficiency and working life of the first color quantum dot light-emitting device and the display panel.

[0123] Figure 12 This is a top view schematic diagram of a display panel provided in an embodiment of this application. (In conjunction with...) Figure 11 and Figure 12 As shown, according to some embodiments of this application, optionally, the first anode 204 and the third anode 404 can both be located in the same anode layer 12a. The first anode 204 and the third anode 404 are electrically connected to form a planar electrode, and a hollow portion 120 is provided in the planar electrode. The hollow portion 120 does not contain anode material. Along the thickness direction Z of the display panel, the hollow portion 120 can overlap with the second color quantum dot light-emitting device 30. That is, along the thickness direction Z of the display panel, the anode layer 12a directly above the second color quantum dot light-emitting device 30 can be hollowed out.

[0124] In this way, on the one hand, since the first anode and the third anode are electrically connected as planar electrodes, the IR-drop of the first anode and the third anode can be reduced; on the other hand, by setting a hollow part in the area overlapping with the second color quantum dot light-emitting device, crosstalk between the first anode and the third anode and the second color quantum dot light-emitting device can be effectively avoided, ensuring the normal light emission of the second color quantum dot light-emitting device.

[0125] For ease of understanding, the following explanation will take the example of a first-color quantum dot light-emitting device and a third-color quantum dot light-emitting device, both of which include two hole transport layers.

[0126] Figure 13 This is yet another cross-sectional view of the display panel provided in an embodiment of this application. For example... Figure 13 As shown, in some specific embodiments, optionally, both the first color quantum dot light-emitting device 20 and the third color quantum dot light-emitting device 40 may include a second hole transport layer 131 and a third hole transport layer 132. Along the thickness direction Z of the display panel, the second hole transport layer 131 may be located between the third hole transport layer 132 and the first quantum dot light-emitting layer 202, and simultaneously, the second hole transport layer 131 may also be located between the third hole transport layer 132 and the third quantum dot light-emitting layer 402. The valence bands of the materials of the first quantum dot light-emitting layer 202 and the third quantum dot light-emitting layer 402 may be smaller than the HOMO energy level of the material of the second hole transport layer 131, and the HOMO energy level of the material of the second hole transport layer 131 is smaller than the HOMO energy level of the material of the third hole transport layer 132.

[0127] In this way, since both the first-color quantum dot light-emitting device and the third-color quantum dot light-emitting device include a second hole transport layer and a third hole transport layer, and the HOMO energy level of the material of the third hole transport layer is greater than the HOMO energy level of the material of the second hole transport layer, which is greater than the valence band of the materials of the first and third quantum dot light-emitting layers, the holes in the third and second hole transport layers can be injected into the first and third quantum dot light-emitting layers in a stepped manner through energy level matching. This increases the number of holes injected into the first and third quantum dot light-emitting layers, reduces the difference between the number of holes and the number of electrons in the first and third quantum dot light-emitting layers, and thus improves the luminous efficiency and working life of the first-color quantum dot light-emitting device and the third-color quantum dot light-emitting device.

[0128] In some specific examples, optionally, the HOMO level of the material of the second hole transport layer 131 may be between -6.1 eV and -5.5 eV.

[0129] In some embodiments, the LUMO energy level of the material of the second hole transport layer 131 can be greater than the conduction band of the material of the first quantum dot emitting layer 202, and the LUMO energy level of the material of the second hole transport layer 131 can be greater than the conduction band of the material of the third quantum dot emitting layer 402. For example, the LUMO energy level of the material of the second hole transport layer 131 can be greater than -3.5 eV.

[0130] In this way, since the LUMO energy level of the material of the second hole transport layer 131 is greater than the conduction band of the materials of the first quantum dot light-emitting layer 202 and the third quantum dot light-emitting layer 402, it can effectively block electrons in the first quantum dot light-emitting layer 202 and the third quantum dot light-emitting layer 402 from entering the second hole transport layer 131. This effectively avoids the degradation of the material of the second hole transport layer 131 due to too many electrons entering the second hole transport layer 131, and improves the lifetime of the material of the second hole transport layer 131.

[0131] In some embodiments, the LUMO energy level of the material of the third hole transport layer 132 may be greater than the LUMO energy level of the material of the second hole transport layer 131.

[0132] In this way, since the LUMO energy level of the material of the third hole transport layer 132 is greater than that of the material of the second hole transport layer 131, it can further effectively block electrons in the second hole transport layer 131 from entering the third hole transport layer 132, effectively avoid the degradation of the material of the third hole transport layer 132 by electrons, and improve the lifetime of the material of the third hole transport layer 132.

[0133] In some specific examples, the material of the second hole transport layer 131 can be 4,4',4”-tris(carbazole-9-yl)triphenylamine, with the following chemical structural formula: Figure 14 As shown. The material of the third hole transport layer 132 can be N,N'-di(1-naphthyl)-N,N'-diphenyl-1,1'-biphenyl-4-4'-diamine, and its chemical structural formula is as follows. Figure 15 As shown.

[0134] See also Figure 13 According to some embodiments of this application, optionally, the first cathode 201, the second cathode and the third cathode 401 can be arranged in the same layer.

[0135] In this way, since the first cathode, the second cathode, and the third cathode are set in the same layer, that is, the first cathode, the second cathode, and the third cathode are prepared by the same process, the number of film layers in the display panel can be reduced, which is conducive to simplifying the production process and reducing production costs.

[0136] like Figure 13 As shown, in some specific embodiments, the second color quantum dot light-emitting device 30 may optionally include a second hole injection layer 305 and a second electron transport layer 306. Along the thickness direction Z of the display panel, the second hole injection layer 305 may be located between the second anode 301 and the first hole transport layer 302, and the second electron transport layer 306 may be located between the second quantum dot light-emitting layer 303 and the second cathode 304. In some embodiments, the second color quantum dot light-emitting device 30 may further include a second electron injection layer (not shown in the figure), which may be located between the second electron transport layer 306 and the second cathode 304 along the thickness direction Z of the display panel.

[0137] The third-color quantum dot light-emitting device 40 may further include a third hole injection layer 405 and a third electron transport layer 406. Along the thickness direction Z of the display panel, the third hole injection layer 405 may be located between the third anode 404 and the hole transport layer 403, and the third electron transport layer 406 may be located between the third quantum dot light-emitting layer 402 and the third cathode 401. In some embodiments, the third-color quantum dot light-emitting device 40 may further include a third electron injection layer (not shown in the figure), which may be located between the third electron transport layer 406 and the third cathode 401 along the thickness direction Z of the display panel.

[0138] In some embodiments, the hole transport layer 403 is made of at least one of the following materials: poly(9,9-dioctylfluorene-CO-N-(4-butylphenyl)diphenylamine), polyvinylcarbazole, poly(N,N'-bis(4-butylphenyl)-N,N'-bis(phenyl)benzidine), poly(9,9-dioctylfluorene-co-bis-N,N-phenyl-1,4-phenylenediamine), 4,4',4”-tris(carbazole-9-yl)triphenylamine, 4,4'-bis(9-carbazole)biphenyl, N,N'-diphenyl-N,N'-di(3-methylphenyl)-1,1'-biphenyl-4,4'-diamine, 15N,N'-diphenyl-N,N'-(1-naphthyl)-1,1'-biphenyl-4,4'-diamine, graphene, and C60.

[0139] In some embodiments, the second hole injection layer 305 and the third hole injection layer 405 include, but are not limited to, at least one of poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS), polythiophene, polyaniline, polypyrrole, and copper phthalocyanine.

[0140] In some embodiments, the materials of the second electron transport layer 306 and the third electron transport layer 406 include, but are not limited to, at least one of ZnO, TiO2, SnO2, Ta2O3, ZrO2, NiO, TiLiO, ZnAlO, ZnMgO, ZnSnO, ZnLiO, and InSnO.

[0141] In some embodiments, the materials of the second electron injection layer and the third electron injection layer include, but are not limited to, at least one of lithium fluoride, sodium fluoride, potassium fluoride, rubidium fluoride, cesium fluoride, lithium oxide, and lithium metaborate.

[0142] In some specific examples, the various film layers in the first color quantum dot light-emitting device 20 can be co-layered with the corresponding film layers in the third color quantum dot light-emitting device 40. For example, the first anode 204 can be co-layered with the third anode 404, the first quantum dot light-emitting layer 202 can be co-layered with the third quantum dot light-emitting layer 402, the hole transport layer 203 can be co-layered with the hole transport layer 403, the first hole injection layer 205 can be co-layered with the third hole injection layer 405, the first electron transport layer 206 can be co-layered with the third electron transport layer 406, and the first cathode 201 can be co-layered with the third cathode 401.

[0143] Based on the display panel provided in the above embodiments, this application also provides specific implementations of the display panel fabrication method. Please refer to the following embodiments. The display panel fabrication method provided in this application can, for example, be used to fabricate the display panel of the above embodiments.

[0144] Figure 16This is a schematic flowchart illustrating a method for manufacturing a display panel according to an embodiment of this application. Figure 16 As shown, the method for manufacturing a display panel provided in this application embodiment may include the following steps S101 and S102.

[0145] S101, Provides a substrate. Combined Figure 2 As shown, substrate 01 may include commonly used rigid substrates such as glass or metal foil, or flexible substrates such as polyimide (PI), polycarbonate (PC), polystyrene (PS), polyethylene (PE), polyvinyl chloride (PV), polyvinylpyrrolidone (PVP), polyethylene terephthalate (PET), etc., which mainly serve a supporting function.

[0146] S102. In a plurality of first regions on the first side of the substrate, a first cathode, a first quantum dot light-emitting layer, at least two hole transport layers and a first anode are sequentially formed to obtain a first color quantum dot light-emitting device.

[0147] It is readily understood that various quantum dot light-emitting devices of different colors can be arranged in an array on the substrate 01. Accordingly, the substrate 01 may include regions corresponding to the various colored quantum dot light-emitting devices. In the region of the substrate 01 corresponding to the first colored quantum dot light-emitting device (i.e., the first region), the first colored quantum dot light-emitting device can be formed.

[0148] Along the thickness direction of the display panel, the i-th hole transport layer in the first color quantum dot light-emitting device is located between the (i+1)-th hole transport layer and the first quantum dot light-emitting layer. The valence band of the material of the first quantum dot light-emitting layer is smaller than the HOMO energy level of the material of the i-th hole transport layer, and the HOMO energy level of the material of the i-th hole transport layer is smaller than the HOMO energy level of the material of the (i+1)-th hole transport layer, where i is a positive integer.

[0149] The method for fabricating a display panel according to embodiments of this application includes a first color quantum dot light-emitting device comprising at least two hole transport layers, wherein the HOMO energy level of the material of the (i+1)th hole transport layer is greater than the HOMO energy level of the material of the ith hole transport layer, and the valence band of the material of the first quantum dot light-emitting layer is greater than that of the material of the first quantum dot light-emitting layer. Therefore, by matching the energy levels, holes in the at least two hole transport layers can be injected into the first quantum dot light-emitting layer in a stepped manner, thereby increasing the number of holes injected into the first quantum dot light-emitting layer, reducing the difference between the number of holes and the number of electrons in the first quantum dot light-emitting layer, and thus improving the luminous efficiency and working life of the first color quantum dot light-emitting device and the display panel.

[0150] Figure 17 This is another schematic flowchart illustrating a method for manufacturing a display panel according to an embodiment of this application. Figure 17As shown, according to some embodiments of this application, optionally, the method for manufacturing a display panel provided in the embodiments of this application may further include the following steps:

[0151] S103. In a plurality of second regions on the first side of the substrate, a second anode, a first hole transport layer, a second quantum dot light-emitting layer and a second cathode are sequentially formed to obtain a second color quantum dot light-emitting device.

[0152] In this way, for second-color quantum dot light-emitting devices with a large valence band in the second quantum dot light-emitting layer, an upright light-emitting device can be used, with only one hole transport layer (i.e., the first hole transport layer) set up. This avoids the number of holes in the second quantum dot light-emitting layer from significantly exceeding the number of electrons, thus better ensuring the balance between the number of holes and electrons in the second quantum dot light-emitting layer, thereby improving the luminous efficiency and working life of the second-color quantum dot light-emitting device.

[0153] Figure 18 This is another schematic flowchart illustrating a method for manufacturing a display panel according to an embodiment of this application. Figure 18 As shown, according to some embodiments of this application, optionally, the method for manufacturing a display panel provided in the embodiments of this application may further include the following steps:

[0154] S104. In a plurality of third regions on the first side of the substrate, a third cathode, a third quantum dot light-emitting layer, at least two hole transport layers and a third anode are sequentially formed to obtain a third color quantum dot light-emitting device.

[0155] In this way, for third-color quantum dot light-emitting devices with a smaller valence band in the third quantum dot light-emitting layer, at least two hole transport layers can still be set up, and the HOMO energy level of the material of the (j+1)th hole transport layer is greater than the HOMO energy level of the material of the jth hole transport layer, which is greater than the valence band of the material of the third quantum dot light-emitting layer. By matching the energy levels, holes from at least two hole transport layers can be injected into the third quantum dot light-emitting layer in a stepped manner, thereby increasing the number of holes injected into the third quantum dot light-emitting layer, reducing the difference between the number of holes and the number of electrons in the third quantum dot light-emitting layer, and thus improving the luminous efficiency and working life of the third-color quantum dot light-emitting device.

[0156] In some embodiments, optionally, at least two hole transport layers in the first-color quantum dot light-emitting device and at least two hole transport layers in the third-color quantum dot light-emitting device can be formed by a vapor deposition process. The first hole transport layer in the second-color quantum dot light-emitting device can be formed by an ink printing process.

[0157] The method for manufacturing a display panel provided in this application includes the same or corresponding technical features as the display panel in the above embodiments. Both can achieve the same or corresponding technical effects, and will not be repeated here for the sake of brevity.

[0158] Based on the display panel provided in the above embodiments, this application also provides a display device, including the display panel provided in this application. Please refer to... Figure 19 , Figure 19 This is a schematic diagram of a display device provided in an embodiment of this application. Figure 19 The provided display device 1000 includes the display panel 100 provided in any of the above embodiments of this application. Figure 19 The embodiments use a mobile phone as an example to describe the display device 1000. It is understood that the display device provided in the embodiments of this application can be other display devices with display functions, such as wearable products, computers, televisions, and in-vehicle display devices. This application does not impose specific limitations on these. The display device provided in the embodiments of this application has the beneficial effects of the display panel 100 provided in the embodiments of this application. For details, please refer to the specific descriptions of the display panel 100 in the above embodiments. These descriptions will not be repeated here.

[0159] In some embodiments, the display device 1000 may be a QLED display device.

[0160] It should be understood that the specific circuit structures and cross-sectional structures of the display panels provided in the accompanying drawings of the embodiments of this application are merely examples and are not intended to limit this application. Furthermore, the above embodiments provided in this application can be combined with each other unless there is contradiction.

[0161] The embodiments described above are not exhaustive, nor do they limit the application to the specific embodiments described herein. Clearly, many modifications and variations can be made based on the above description. These embodiments are selected and specifically described in this specification to better explain the principles and practical applications of this application, thereby enabling those skilled in the art to effectively utilize this application and its modifications. This application is limited only by the claims and their full scope and equivalents.

[0162] The above description is merely a specific implementation of this application. Those skilled in the art will clearly understand that, for the sake of convenience and brevity, the specific working processes of the systems, modules, and units described above can be referred to the corresponding processes in the foregoing method embodiments, and will not be repeated here. It should be understood that the protection scope of this application is not limited thereto. Any person skilled in the art can easily conceive of various equivalent modifications or substitutions within the technical scope disclosed in this application, and these modifications or substitutions should all be covered within the protection scope of this application.

Claims

1. A display panel, characterized in that, The display panel includes a substrate arranged sequentially along the thickness direction, a driving device layer including a first pixel circuit, a second pixel circuit and a third pixel circuit, and a first color quantum dot light-emitting device, a second color quantum dot light-emitting device and a third color quantum dot light-emitting device located on the driving device layer. The second color quantum dot light-emitting device is a positive light-emitting device, and the first color quantum dot light-emitting device and the third color quantum dot light-emitting device are inverted light-emitting devices. The first color quantum dot light-emitting device includes a first cathode, a first quantum dot light-emitting layer, at least two hole transport layers and a first anode stacked together, wherein the first cathode is located on the side of the first anode closer to the substrate; The second color quantum dot light-emitting device includes a second anode, a first hole transport layer, a second quantum dot light-emitting layer, and a second cathode stacked together. The second anode is located on the side of the second cathode closer to the substrate. The valence band of the material of the first quantum dot light-emitting layer is smaller than the valence band of the material of the second quantum dot light-emitting layer. The third color quantum dot light-emitting device includes a third cathode, a third quantum dot light-emitting layer, at least two hole transport layers, and a third anode stacked together. The third cathode is located on the side of the third anode closer to the substrate. The valence band of the material of the third quantum dot light-emitting layer is smaller than the valence band of the material of the second quantum dot light-emitting layer. Each film layer in the first color quantum dot light-emitting device is co-layered with the corresponding film layer in the third color quantum dot light-emitting device. Along the thickness direction of the display panel, the i-th hole transport layer in the first color quantum dot light-emitting device is located between the (i+1)-th hole transport layer and the first quantum dot light-emitting layer. The valence band of the material of the first quantum dot light-emitting layer is smaller than the highest occupied molecular orbital (HOMO) energy level of the material of the i-th hole transport layer, and the HOMO energy level of the material of the i-th hole transport layer is smaller than the HOMO energy level of the material of the (i+1)-th hole transport layer, where i is a positive integer. The second pixel circuit includes a second N-type transistor, the gate of which is electrically connected to the second target node, the source of which is electrically connected to a ground terminal or a negative voltage signal terminal, the drain of which is electrically connected to the second cathode, and the second anode is electrically connected to a positive voltage signal terminal. The second color quantum dot light-emitting device is located in the pixel opening, and the second cathode includes a first body portion that overlaps with the pixel opening along the thickness direction of the display panel and an extension portion that does not overlap with the pixel opening along the thickness direction of the display panel; Along the thickness direction of the display panel, at least a portion of the orthographic projection of the extension on the substrate overlaps with the orthographic projection of the second N-type transistor on the substrate, and the extension is electrically connected to the drain of the second N-type transistor through a first via formed on the driving device layer; The first anode and the third anode are electrically connected, and are electrically connected to the second anode through a first overlap portion. The thickness of the second anode is greater than or equal to 30 nm and less than or equal to 500 nm.

2. The display panel according to claim 1, characterized in that, Along the thickness direction of the display panel, the j-th hole transport layer in the third color quantum dot light-emitting device is located between the (j+1)-th hole transport layer and the third quantum dot light-emitting layer. The valence band of the material of the third quantum dot light-emitting layer is smaller than the HOMO level of the material of the j-th hole transport layer, and the HOMO level of the material of the j-th hole transport layer is smaller than the HOMO level of the material of the (j+1)-th hole transport layer, where j is a positive integer.

3. The display panel according to claim 1, characterized in that, In the first color quantum dot light-emitting device, the lowest unoccupied molecular orbital (LUMO) energy level of the material of the i-th hole transport layer is greater than the conduction band of the material of the first quantum dot light-emitting layer; and / or, The LUMO energy level of the material of the j-th hole transport layer in the third color quantum dot light-emitting device is greater than the conduction band of the material of the third quantum dot light-emitting layer.

4. The display panel according to claim 3, characterized in that, The LUMO energy level of the material of the (i+1)th hole transport layer in the first color quantum dot light-emitting device is greater than the LUMO energy level of the material of the ith hole transport layer in the first color quantum dot light-emitting device, and / or, the LUMO energy level of the material of the (j+1)th hole transport layer in the third color quantum dot light-emitting device is greater than the LUMO energy level of the material of the jth hole transport layer in the third color quantum dot light-emitting device.

5. The display panel according to claim 1, characterized in that, The first pixel circuit includes a first N-type transistor, the gate of the first N-type transistor is electrically connected to the first target node, the source of the first N-type transistor is electrically connected to a ground terminal or a negative voltage signal terminal, the drain of the first N-type transistor is electrically connected to the first cathode, and the first anode is electrically connected to the positive voltage signal terminal. The third pixel circuit includes a third N-type transistor, the gate of which is electrically connected to the third target node, the source of which is electrically connected to a ground terminal or a negative voltage signal terminal, the drain of which is electrically connected to the third cathode, and the second anode is electrically connected to the positive voltage signal terminal.

6. The display panel according to claim 5, characterized in that, Along the thickness direction of the display panel, the orthographic projection of the first cathode on the substrate overlaps with the orthographic projection of the first N-type transistor on the substrate, and the first cathode is electrically connected to the drain of the first N-type transistor through a second via formed in the driving device layer.

7. The display panel according to claim 5, characterized in that, Along the thickness direction of the display panel, the orthographic projection of the third cathode on the substrate overlaps with the orthographic projection of the third N-type transistor on the substrate, and the third cathode is electrically connected to the drain of the third N-type transistor through a third via formed in the driving device layer.

8. The display panel according to claim 1, characterized in that, The thickness of each hole transport layer is greater than or equal to 50 angstroms and less than or equal to 2000 angstroms.

9. The display panel according to claim 1, characterized in that, The first anode and the third anode are both located in the same anode layer. The first anode and the third anode are electrically connected to form a planar electrode. The planar electrode has a hollow portion. Along the thickness direction of the display panel, the hollow portion overlaps with the second color quantum dot light-emitting device.

10. The display panel according to claim 1, characterized in that, Both the first color quantum dot light-emitting device and the third color quantum dot light-emitting device include a second hole transport layer and a third hole transport layer. Along the thickness direction of the display panel, the second hole transport layer is located between the third hole transport layer and the first quantum dot light-emitting layer and the third quantum dot light-emitting layer. The valence bands of the materials of the first quantum dot emitting layer and the third quantum dot emitting layer are both smaller than the HOMO energy level of the material of the second hole transport layer, and the HOMO energy level of the material of the second hole transport layer is smaller than the HOMO energy level of the material of the third hole transport layer.

11. The display panel according to claim 1, characterized in that, The first cathode, the second cathode, and the third cathode are disposed in the same layer.

12. A method for manufacturing a display panel, characterized in that, A method for preparing a display panel according to any one of claims 1 to 11, the method comprising: Provide substrate; In a plurality of first regions on a first side of the substrate, a first cathode, a first quantum dot light-emitting layer, at least two hole transport layers and a first anode are sequentially formed to obtain the first color quantum dot light-emitting device; Along the thickness direction of the display panel, the i-th hole transport layer in the first color quantum dot light-emitting device is located between the (i+1)-th hole transport layer and the first quantum dot light-emitting layer. The valence band of the material of the first quantum dot light-emitting layer is smaller than the HOMO level of the material of the i-th hole transport layer, and the HOMO level of the material of the i-th hole transport layer is smaller than the HOMO level of the material of the (i+1)-th hole transport layer, where i is a positive integer.

13. A display device, characterized in that, Includes the display panel as described in any one of claims 1 to 11.

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