Light-emitting device and display panel

Abstract

The present disclosure belongs to the technical field of display. Provided are a light-emitting device and a display panel. The light-emitting device of the present disclosure comprises an anode, a cathode, a plurality of light-emitting units, which are provided between the anode and the cathode, and charge generation units, which each are provided between adjacent light-emitting units, wherein the plurality of light-emitting units comprise one first light-emitting unit and one second light-emitting unit, and the first light-emitting unit is closer to the anode than the second light-emitting unit; the first light-emitting unit comprises a first light-emitting layer, and a first hole transport subunit, which is provided on the side of the first light-emitting layer that is close to the anode; the second light-emitting unit comprises a second light-emitting layer, and a second hole transport subunit, which is provided on the side of the second light-emitting layer that is close to the anode; and the thickness of the first hole transport subunit of the first light-emitting unit is greater than that of the second hole transport subunit of the second light-emitting unit.

Description

Light-emitting device and display panel TECHNICAL FIELD

[0001] The present disclosure belongs to the technical field of display, and particularly relates to a light-emitting device and a display panel. BACKGROUND

[0002] Tandem OLEDs (Tandem Organic Light-Emitting Diodes) emerge in the development of OLEDs (Organic Light-Emitting Diodes). Tandem OLEDs have the advantages of high efficiency and high brightness. However, the Tandem OLEDs in the related art have the problem that the light-emitting efficiency and the lifespan of light-emitting devices of different colors are inconsistent. SUMMARY

[0003] The present disclosure aims to at least solve one of the technical problems existing in the prior art, and provides a light-emitting device and a display panel.

[0004] In a first aspect, a technical solution adopted to solve the technical problems of the present disclosure is a light-emitting device, comprising an anode, a cathode, a plurality of light-emitting units arranged between the anode and the cathode, and a charge generation unit arranged between adjacent light-emitting units; the plurality of light-emitting units comprises at least a first light-emitting unit and a second light-emitting unit, and the first light-emitting unit is closer to the anode than the second light-emitting unit; the first light-emitting unit comprises a first light-emitting layer and a first hole transport sub-unit arranged on a side of the first light-emitting layer close to the anode; the second light-emitting unit comprises a second light-emitting layer and a second hole transport sub-unit arranged on a side of the second light-emitting layer close to the anode; and the thickness of the first hole transport sub-unit of the first light-emitting unit is greater than the thickness of the second hole transport sub-unit of the second light-emitting unit.

[0005] In some embodiments, the charge generation unit comprises an N-type doped charge generation layer and a P-type doped charge generation layer arranged in sequence in a direction away from the anode; a surface of the N-type doped charge generation layer in contact with the P-type doped charge generation layer is a first surface; a surface of the first light-emitting layer close to the N-type doped charge generation layer is a second surface, and the distance from the first surface to the second surface is a first distance; and the ratio of the thickness of the first hole transport sub-unit to the first distance is between 4 and 10.

[0006] In some embodiments, the first distance is between 15 nm and 30 nm.

[0007] In some embodiments, the first light-emitting unit further comprises a first hole-blocking layer disposed on the first light-emitting layer close to the cathode; the thickness of the first hole-blocking layer is between 5 nm and 10 nm.

[0008] In some embodiments, the first hole-transporting sub-unit comprises at least a first hole-transporting layer; the second hole-transporting sub-unit comprises at least a second hole-transporting layer; the structural general formula (I) of the material of the first hole-transporting layer and the material of the second hole-transporting layer is as follows:

[0009] wherein, Ar1-Ar3 are each independently selected from any one of hydrogen, deuterium, nitrile group, nitro group, hydroxyl group, carbonyl group, ester group, imide group, amide group, alkyl group, cycloalkyl group, alkoxy group, aryloxy group, alkylthio group, arylthio group, alkylsulfonyl group, arylsulfonyl group, alkenyl group, silyl group, boron group, amine group, aryl phosphine group, phosphine oxide group, aryl group, heteroaryl group; or, any adjacent groups among Ar1-Ar3 combine to form a ring; N represents a nitrogen atom.

[0010] In some embodiments, the first hole-transporting sub-unit comprises at least a first hole-transporting layer; the second hole-transporting sub-unit comprises at least a second hole-transporting layer; the structural general formula (II) of the material of the first hole-transporting layer and the material of the second hole-transporting layer is as follows:

[0011] wherein, Ar4-Ar7 are each independently selected from any one of hydrogen, deuterium, nitrile group, nitro group, hydroxyl group, carbonyl group, ester group, imide group, amide group, alkyl group, cycloalkyl group, alkoxy group, aryloxy group, alkylthio group, arylthio group, alkylsulfonyl group, arylsulfonyl group, alkenyl group, silyl group, boron group, amine group, aryl phosphine group, phosphine oxide group, aryl group, heteroaryl group; or, any adjacent groups among Ar4-Ar7 combine to form a ring; L represents a substituted or unsubstituted arylene group or heteroarylene group.

[0012] In some embodiments, Ar1-Ar3 are selected from any one of the following structures:

[0013] wherein, * represents the position of connecting the structural general formula (I) or the position of connecting the structural general formula (II).

[0014] In some embodiments, Ar4-Ar7 are selected from any one of the following structures:

[0015] wherein, * represents the position of connecting the structural general formula (I) or the position of connecting the structural general formula (II).

[0016] In some embodiments, L is selected from any one of the following structures:

[0017] In some embodiments, the first hole transport sub-unit comprises, in sequence from the direction away from the anode, a first hole injection layer, a first hole transport layer, and a first electron blocking layer; and the second hole transport sub-unit comprises, in sequence from the direction away from the anode, a second hole transport layer and a second electron blocking layer.

[0018] In a second aspect, the present disclosure also provides a display panel comprising a plurality of light emitting devices of different colors, the plurality of light emitting devices of different colors comprising red light emitting devices, green light emitting devices, and blue light emitting devices; each light emitting device comprising an anode, a cathode, a plurality of light emitting units disposed between the anode and the cathode, and a charge generation unit disposed between adjacent light emitting units; at least one first light emitting unit and one second light emitting unit in the plurality of light emitting units, and the first light emitting unit being closer to the anode than the second light emitting unit; the first light emitting unit comprising a first light emitting layer and a first hole transport sub-unit disposed on a side of the first light emitting layer close to the anode; the second light emitting unit comprising a second light emitting layer and a second hole transport sub-unit disposed on a side of the second light emitting layer close to the anode; and a thickness of the first hole transport sub-unit of the first light emitting unit being greater than a thickness of the second hole transport sub-unit of the second light emitting unit.

[0019] In some embodiments, the charge generation unit comprises, in sequence from the direction away from the anode, an N-type doped charge generation layer and a P-type doped charge generation layer; a surface of the N-type doped charge generation layer in contact with the P-type doped charge generation layer is a first surface; a surface of the first light emitting layer close to the N-type doped charge generation layer is a second surface, and a distance from the first surface to the second surface is a first distance; for the red light emitting device, a ratio of the thickness of the first hole transport sub-unit to the first distance is between 6 and 10; for the green light emitting device, a ratio of the thickness of the first hole transport sub-unit to the first distance is between 5 and 8; and for the blue light emitting device, a ratio of the thickness of the first hole transport sub-unit to the first distance is between 4 and 6.

[0020] In some embodiments, the thickness of the first hole transport sub-unit of the red light emitting device is greater than the thickness of the first hole transport sub-unit of the green light emitting device; and the thickness of the first hole transport sub-unit of the green light emitting device is greater than the thickness of the first hole transport sub-unit of the blue light emitting device.

[0021] In some embodiments, the thickness of the first hole transport sub-unit is between 170 nm and 230 nm for the red light emitting device; the thickness of the first hole transport sub-unit is between 130 nm and 170 nm for the green light emitting device; and the thickness of the first hole transport sub-unit is between 90 nm and 130 nm for the blue light emitting device.

[0022] In some embodiments, the first distance is between 15 nm and 30 nm.

[0023] In some embodiments, the charge generation unit comprises an N-type doped charge generation layer and a P-type doped charge generation layer arranged in sequence in a direction away from the anode; a surface of the N-type doped charge generation layer in contact with the P-type doped charge generation layer is a first surface; a surface of the second light emitting layer close to the N-type doped charge generation layer is a third surface, and a distance from the third surface to the first surface is a second distance; a surface of the second light emitting layer close to the cathode side is a fourth surface, and a shortest distance from the fourth surface to the cathode is a third distance; for the red light emitting device, a ratio of the second distance to the third distance is between 2 and 3.2; for the green light emitting device, a ratio of the second distance to the third distance is between 1.8 and 2.8; and for the blue light emitting device, a ratio of the second distance to the third distance is between 1.6 and 2.6.

[0024] In some embodiments, the second distance is between 80 nm and 110 nm for the red light emitting device; the second distance is between 65 nm and 95 nm for the green light emitting device; and the second distance is between 55 nm and 85 nm for the blue light emitting device.

[0025] In some embodiments, the thickness of the second hole transport sub-unit is between 70 nm and 90 nm for the red light emitting device; the thickness of the second hole transport sub-unit is between 60 nm and 80 nm for the green light emitting device; and the thickness of the second hole transport sub-unit is between 50 nm and 70 nm for the blue light emitting device.

[0026] In some embodiments, the first hole transport sub-unit comprises a first hole injection layer, a first hole transport layer, and a first electron blocking layer arranged in sequence in a direction away from the anode; and the second hole transport sub-unit comprises a second hole transport layer and a second electron blocking layer arranged in sequence in a direction away from the anode.

[0027] In some embodiments, the first hole injection layer of the plurality of light emitting devices has a same thickness, and the first hole injection layer of the plurality of light emitting devices has an integrated structure; and the first hole transport layer of the plurality of light emitting devices has a same thickness, and the first hole transport layer of the plurality of light emitting devices has an integrated structure.

[0028] In some embodiments, the first electron blocking layer of the red light emitting device has a thickness greater than that of the first electron blocking layer of the green light emitting device; and the first electron blocking layer of the green light emitting device has a thickness greater than that of the first electron blocking layer of the blue light emitting device.

[0029] In some embodiments, the second electron blocking layer of the red light emitting device has a thickness greater than that of the second electron blocking layer of the green light emitting device; and the second electron blocking layer of the green light emitting device has a thickness greater than that of the second electron blocking layer of the blue light emitting device.

[0030] In some embodiments, the material of the first electron blocking layer corresponding to each of the red light emitting device, the green light emitting device and the blue light emitting device is different; the material of the second electron blocking layer corresponding to each of the red light emitting device, the green light emitting device and the blue light emitting device is different; and the material of the first light emitting layer corresponding to each of the red light emitting device, the green light emitting device and the blue light emitting device is different; the material of the second light emitting layer corresponding to each of the red light emitting device, the green light emitting device and the blue light emitting device is different. BRIEF DESCRIPTION OF DRAWINGS

[0031] FIG. 1 is a structural schematic diagram of a light emitting device according to an embodiment of the present disclosure;

[0032] FIG. 2 is a schematic diagram of a subunit of a light emitting unit according to an embodiment of the present disclosure;

[0033] FIG. 3 is a schematic diagram of a specific structure of a carrier transport subunit according to an embodiment of the present disclosure;

[0034] FIG. 4 is a schematic diagram of a spacing between film layers in a light emitting device according to an embodiment of the present disclosure;

[0035] FIG. 5 is a schematic diagram of a specific structure of another carrier transport subunit according to an embodiment of the present disclosure;

[0036] FIG. 6 is a schematic diagram of a display panel according to an embodiment of the present disclosure. DETAILED DESCRIPTION

[0037] In order to make the objects, technical solutions and advantages of the embodiments of the present disclosure clearer, the following will be combined with the accompanying drawings to make a clear and complete description of the technical solutions of the embodiments of the present disclosure. Obviously, the described embodiments are only a part of the embodiments of the present disclosure, rather than all the embodiments. The components of the embodiments of the present disclosure generally described and shown in the accompanying drawings can be arranged and designed in various different configurations. Therefore, the following detailed description of the embodiments of the present disclosure provided in the accompanying drawings is not intended to limit the scope of the claimed present disclosure, but only represents selected embodiments of the present disclosure. Based on the embodiments of the present disclosure, all other embodiments obtained by those skilled in the art without creative work fall within the scope of protection of the present disclosure.

[0038] Unless otherwise defined, technical or scientific terms used in the present disclosure should be understood as having the same meaning as commonly understood by one of ordinary skill in the art to which the present disclosure belongs. The terms "first", "second" and similar terms used in the present disclosure do not denote any order, quantity or importance, but are used to distinguish different components. Similarly, the terms "one", "a" or "the" and similar terms do not denote quantity limitation, but mean that there is at least one. The terms "include" or "contain" and similar terms mean that the elements or objects before the terms encompass the elements or objects listed after the terms and their equivalents, and do not exclude other elements or objects. The terms "connect" or "connected" and similar terms are not limited to physical or mechanical connections, but can include electrical connections, whether direct or indirect. The terms "up", "down", "left", "right" and the like are only used to represent relative positional relationships, and when the absolute positions of the described objects are changed, the relative positional relationships may also be changed accordingly.

[0039] In the present disclosure, "a plurality of or several" refers to two or more. The term "and / or" describes the association relationship of the associated objects, which means that there can be three relationships, for example, A and / or B, which can represent three cases: A exists alone, A and B exist together, and B exists alone. The character " / " generally represents that the associated objects before and after it are in an "or" relationship.

[0040] In the related art, the carrier transport path in the Tandem device includes: in the first light-emitting unit, holes are transported from the anode to the first light-emitting layer; and electrons are transported from the interface between the N-CGL layer (N-type doped charge generation layer) and the P-CGL layer (P-type doped charge generation layer) to the first light-emitting layer. In the second light-emitting unit, holes are transported from the interface between the N-CGL layer and the P-CGL layer to the second light-emitting layer; and electrons are transported from the cathode to the second light-emitting layer. However, a hole blocking layer is often arranged between the N-CGL layer and the first light-emitting layer, which is a combination of one or more organic layers, mainly used for transporting electrons and blocking holes; in addition, when the hole blocking layer is in direct contact with the N-CGL layer, it is also used to block the metal ions doped in the N-CGL layer to prevent the migration of metal ions, so there is a large energy level barrier between the hole blocking layer and the N-CGL layer, resulting in a low electron transport rate. At the same time, the hole transport material currently used has a faster hole transport speed and a higher hole injection efficiency, which causes an imbalance in the transport rates of holes and electrons, ultimately leading to the inability of holes and electrons to recombine in the first light-emitting layer or a small recombination area, thereby affecting the luminous efficiency and service life of the light-emitting device. That is, in the first light-emitting layer close to the N-CGL layer, it takes a longer time for electrons to transport to the first light-emitting layer, so in the case of a large hole transport rate, the thickness of the first hole transport sub-unit 311 close to the first light-emitting layer needs to be increased to slow down the arrival of holes in the first light-emitting layer.

[0041] In view of this, the embodiments of the present disclosure provide a light-emitting device which substantially eliminates one or more problems caused by the limitations and defects of the related art.

[0042] FIG. 1 is a structural schematic diagram of a light-emitting device provided by the embodiments of the present disclosure, as shown in FIG. 1, the light-emitting device includes an anode 1, a cathode 2, a plurality of light-emitting units arranged between the anode 1 and the cathode 2, and a charge generation unit 4 arranged between adjacent light-emitting units. Among them, the plurality of light-emitting units at least includes a first light-emitting unit 31 and a second light-emitting unit 32, and the first light-emitting unit 31 is closer to the anode 1 than the second light-emitting unit 32. That is, the light-emitting device of the present disclosure is a Tandem OLED device, which has the advantages of high efficiency and high brightness.

[0043] FIG. 2 is a schematic diagram of a subunit of a light-emitting unit according to an embodiment of the present disclosure. As shown in FIG. 1, the first light-emitting unit 31 includes a first light-emitting layer EML1 and a first hole transport subunit 311 disposed on a side of the first light-emitting layer EML1 close to the anode 1; and the second light-emitting unit 32 includes a second light-emitting layer EML2 and a second hole transport subunit 321 disposed on a side of the second light-emitting layer EML2 close to the anode 1. The first hole transport subunit 311 is mainly used for transporting holes generated by the anode 1 or the charge generation unit 4, thereby improving the hole transport efficiency. The second hole transport subunit 321 is mainly used for transporting holes generated by the charge generation unit 4, thereby improving the hole transport efficiency.

[0044] As shown in FIG. 2, the first light-emitting unit 31 further includes a first electron transport subunit 312 disposed on a side of the first light-emitting layer EML1 close to the cathode 2; and the second light-emitting unit 32 further includes a second electron transport subunit 322 disposed on a side of the second light-emitting layer EML2 close to the cathode 2. The first electron transport subunit 312 is mainly used for transporting electrons generated by the charge generation unit 4, thereby improving the electron transport efficiency; and the second electron transport subunit 322 is mainly used for transporting electrons generated by the cathode 2, thereby improving the electron transport efficiency.

[0045] For example, the plurality of light-emitting units includes one first light-emitting unit 31 and one second light-emitting unit 32. For another example, the plurality of light-emitting units includes a plurality of first light-emitting units 31 and one second light-emitting unit 32. In the case of including a plurality of first light-emitting units 31 and one second light-emitting unit 32, the thickness of the first hole transport subunit 311 of at least some of the first light-emitting units 31 is greater than the thickness of the second hole transport subunit 321 of the second light-emitting unit 32.

[0046] For example, the light-emitting device includes one first light-emitting unit 31, one charge generation unit 4 and one second light-emitting unit 32. Under the action of an electric field, the anode 1 in the light-emitting device generates holes, and the cathode 2 generates electrons; the charge generation unit 4 also generates holes and electrons, and separates them. The holes generated by the anode 1 are transported to the first light-emitting layer EML1 through the first hole transport subunit 311, and the electrons generated by the charge generation unit 4 can be transported to the first light-emitting layer EML1 through the first electron transport subunit 312; and the holes generated by the charge generation unit 4 are transported to the second light-emitting layer EML2 through the second hole transport subunit 321, and the electrons generated by the cathode 2 can be transported to the second light-emitting layer EML2 through the second electron transport subunit 322. The holes and the electrons migrate to the first light-emitting layer EML1 (or the second light-emitting layer EML2), and excitons are generated in the first light-emitting layer EML1 (or the second light-emitting layer EML2) by recombination, and the excitons radiate light by jumping transition.

[0047] FIG. 3 is a schematic diagram of a specific structure of a carrier transport subunit according to an embodiment of the present disclosure. As shown in FIG. 3, for example, the first hole transport subunit 311 includes at least a first hole transport layer HTL1, the second hole transport subunit 321 includes at least a second hole transport layer HTL2, the first electron transport subunit 312 includes at least a first hole blocking layer HBL1, and the second electron transport subunit 322 includes at least a second hole blocking layer HBL2. The first hole blocking layer HBL1 is a combination of one or more organic layers, and is mainly used for transporting electrons and blocking holes. In addition, when the first hole blocking layer HBL1 is in direct contact with the charge generation unit 4, the first hole blocking layer HBL1 is also used for blocking metal ions doped in the charge generation unit 4 to prevent migration of the metal ions. Therefore, there is a large energy level barrier between the first hole blocking layer HBL1 and the charge generation unit 4, resulting in a low electron transport rate.

[0048] In the embodiment of the present disclosure, the thickness of the first hole transport subunit 311 of the first light emitting unit 31 is greater than the thickness of the second hole transport subunit 321 of the second light emitting unit 32. Compared with the prior art, by adjusting the thickness of the first hole transport subunit 311 and / or the thickness of the second hole transport subunit 321 of each color light emitting device, for example, by increasing the thickness of the first hole transport subunit 311 of the first light emitting unit 31, the thickness of the first hole transport subunit 311 is greater than the thickness of the second hole transport subunit 321, that is, the hole transport path of the anode 1→the first light emitting layer EML1 is increased, so as to increase the transport time of holes in the first hole transport subunit 311, thereby balancing the hole transport rate of the anode 1→the first light emitting layer EML1 and the electron transport rate of the charge generation unit 4→the first light emitting layer EML1, so as to ensure that holes and electrons reach and recombine in the first light emitting layer EML1 at the same time, thereby ensuring the light emitting stability of the light emitting device.

[0049] In some embodiments, as shown in FIG. 3, the charge generation unit 4 includes an N-type doped charge generation layer N-CGL and a P-type doped charge generation layer P-CGL arranged in sequence away from the anode 1; the surface of the N-type doped charge generation layer N-CGL in contact with the P-type doped charge generation layer P-CGL is a first surface; the surface of the first light emitting layer EML1 close to the N-type doped charge generation layer N-CGL is a second surface, and the distance between the first surface and the second surface is a first distance L1. Here, the first distance L1 can be understood as the transport distance of the electrons generated by the charge generation unit 4, that is, the length of the electron transport path from the starting point of generation to the first light emitting layer EML1.

[0050] Since the materials of the light-emitting layers of different color light-emitting devices are different, the materials of the sub-film layers in the first hole transport sub-unit 311 can be different, and thus the hole mobility corresponding to different color light-emitting devices and the energy level difference between the film layers are different.

[0051] In some embodiments, the ratio of the thickness of the first hole transport sub-unit 311 to the first distance L1 is between 4 and 10.

[0052] FIG. 4 is a schematic diagram of the spacing between the film layers in the light-emitting device according to an embodiment of the present disclosure. As shown in FIG. 4, when the light-emitting device is a red light-emitting device R, the ratio of the thickness R_H of the first hole transport sub-unit 311 to the first distance L1 is between 6 and 10. In this embodiment, for the first light-emitting unit 31 corresponding to the red light-emitting device R, the length of the hole transport path and the length of the electron transport path in the first light-emitting unit 31 are adjusted in coordination so that the ratio of the thickness R_H of the first hole transport sub-unit 311 to the first distance L1 is between 6 and 10, thereby ensuring the transport balance of the carriers (holes and electrons) in the red light-emitting device R.

[0053] Specifically, when the light-emitting device is a green light-emitting device G, the ratio of the thickness G_H of the first hole transport sub-unit 311 to the first distance L1 is between 5 and 8. In this embodiment, for the first light-emitting unit 31 corresponding to the green light-emitting device G, the length of the hole transport path and the length of the electron transport path in the first light-emitting unit 31 are adjusted in coordination so that the ratio of the thickness G_H of the first hole transport sub-unit 311 to the first distance L1 is between 5 and 8, thereby ensuring the transport balance of the carriers (holes and electrons) in the green light-emitting device G.

[0054] Specifically, when the light-emitting device is a blue light-emitting device B, the ratio of the thickness B_H of the first hole transport sub-unit 311 to the first distance L1 is between 4 and 6. In this embodiment, for the first light-emitting unit 31 corresponding to the blue light-emitting device B, the length of the hole transport path and the length of the electron transport path in the first light-emitting unit 31 are adjusted in coordination so that the ratio of the thickness B_H of the first hole transport sub-unit 311 to the first distance L1 is between 4 and 6, thereby ensuring the transport balance of the carriers (holes and electrons) in the blue light-emitting device B.

[0055] In a possible implementation, as shown in FIG. 4, the thickness R_H of the first hole transport sub-unit of the red light-emitting device is greater than the thickness G_H of the first hole transport sub-unit of the green light-emitting device; and the thickness G_H of the first hole transport sub-unit of the green light-emitting device is greater than the thickness B_H of the first hole transport sub-unit of the blue light-emitting device.

[0056] In one possible implementation, as shown in FIG. 4, when the light emitting device is a red light emitting device R, the thickness R H of the first hole transport sub-unit 311 is between 170 nm and 230 nm. This implementation balances the hole and electron transport rates by increasing the thickness R H of the first hole transport sub-unit 311 of the red light emitting device R, i.e., the length of the hole transport path, to reduce the hole transport rate, so that the hole and electron recombine in the first light emitting layer REML1, thereby ensuring the light emitting stability of the red light emitting device R, as compared to the prior art (the thickness of the first hole transport sub-unit 311 of the red light emitting device R is about 65 nm).

[0057] Optionally, the thickness R H of the first hole transport sub-unit 311 is 170 nm, 200 nm, or 230 nm.

[0058] In one possible implementation, as shown in FIG. 4, when the light emitting device is a green light emitting device G, the thickness G H of the first hole transport sub-unit 311 is between 130 nm and 170 nm. This implementation balances the hole and electron transport rates by increasing the thickness G H of the first hole transport sub-unit 311 of the green light emitting device G, i.e., the length of the hole transport path, to reduce the hole transport rate, so that the hole and electron recombine in the first light emitting layer GEML1, thereby ensuring the light emitting stability of the green light emitting device G, as compared to the prior art (the thickness of the first hole transport sub-unit 311 of the green light emitting device G is about 45 nm).

[0059] Optionally, the thickness G H of the first hole transport sub-unit 311 is 130 nm, 150 nm, or 170 nm.

[0060] In one possible implementation, as shown in FIG. 4, when the light emitting device is a blue light emitting device B, the thickness B H of the first hole transport sub-unit 311 is between 90 nm and 130 nm. This implementation balances the hole and electron transport rates by increasing the thickness B H of the first hole transport sub-unit 311 of the blue light emitting device B, i.e., the length of the hole transport path, to reduce the hole transport rate, so that the hole and electron recombine in the first light emitting layer BEML1, thereby ensuring the light emitting stability of the blue light emitting device B, as compared to the prior art (the thickness of the first hole transport sub-unit 311 of the blue light emitting device B is about 35 nm).

[0061] In some embodiments, the first hole transport sub-unit 311 includes at least one of a first hole injection layer HIL1, a first hole transport layer HTL1, and a first electron blocking layer EBL1.

[0062] Exemplarily, as shown in FIG. 3, the first hole transport sub-unit 311 comprises a first hole injection layer HIL1, a first hole transport layer HTL1, and a first electron blocking layer EBL1 arranged in sequence in a direction away from the anode 1. The first hole injection layer HIL1 is mainly used to improve the hole injection efficiency, thereby improving the hole transport efficiency. The first hole transport layer HTL1 is mainly used to transport the holes generated by the anode 1 or the charge generation unit 4, so as to improve the hole transport efficiency. The first electron blocking layer EBL1 is mainly used to block the electrons and transport the holes.

[0063] The thicknesses of the first electron blocking layers EBL1 of the light emitting devices of different colors can be increased respectively, so as to balance the transport rates of the holes and the electrons. And / or, the thicknesses of the first hole transport layers HTL1 of the light emitting devices of different colors can be increased respectively, so as to balance the transport rates of the holes and the electrons.

[0064] Exemplarily, as shown in FIG. 4, the thicknesses of the first hole injection layers HIL1 corresponding to the red light emitting device R, the green light emitting device G, and the blue light emitting device B are the same, for example, 10 nm, and the first hole injection layers HIL1 corresponding to the red light emitting device R, the green light emitting device G, and the blue light emitting device B have an integrated structure. The thicknesses of the first hole transport layers HTL1 corresponding to the red light emitting device R, the green light emitting device G, and the blue light emitting device B are the same, for example, 100 nm, and the first hole transport layers HTL1 corresponding to the red light emitting device R, the green light emitting device G, and the blue light emitting device B have an integrated structure. The thicknesses of the first electron blocking layers EBL1 corresponding to the red light emitting device R, the green light emitting device G, and the blue light emitting device B are different. For example, the thickness of the first electron blocking layer REBL1 corresponding to the red light emitting device R is greater than the thickness of the first electron blocking layer GEBL1 corresponding to the green light emitting device G; and the thickness of the first electron blocking layer GEBL1 corresponding to the green light emitting device G is greater than the thickness of the first electron blocking layer BEBL1 corresponding to the blue light emitting device B. For example, the thickness of the first electron blocking layer REBL1 corresponding to the red light emitting device R is 90 nm; the thickness of the first electron blocking layer GEBL1 corresponding to the green light emitting device G is 40 nm; and the thickness of the first electron blocking layer BEBL1 corresponding to the blue light emitting device B is 5 nm.

[0065] In some embodiments, as shown in FIG. 4, the contact interface between the N-type doped charge generation layer N-CGL and the P-type doped charge generation layer P-CGL is a first surface, the distance between the first surface and the second surface of the first emitting layer EML1 closest to the N-type doped charge generation layer N-CGL is denoted as the first distance L1. The first distance L1 is between 15 nm and 30 nm. By adjusting the first distance L1, i.e. the length of the electron transport path generated by the charge generation unit 4, the transport rate of the holes generated by the anode 1 and the transport rate of the electrons generated by the charge generation unit 4 are balanced, and a high-efficiency and stable tandem light-emitting device is achieved.

[0066] In a possible implementation, the first distance L1 can be adjusted by adjusting the thickness of the first electron transport sub-unit 312. As shown in FIG. 3 or FIG. 4, the first electron transport sub-unit 312 at least includes a first hole blocking layer HBL1. The first hole blocking layer HBL1 is mainly used for blocking holes, blocking metal ions doped in the N-type doped charge generation layer N-CGL, and transporting electrons.

[0067] Specifically, the thickness of the first hole blocking layer HBL1 is between 5 nm and 10 nm.

[0068] Compared with the prior art, by thinning the thickness of the first hole blocking layer HBL1, i.e. shortening the length of the electron transport path, the electron transport rate is improved, and the transport rates of holes and electrons are balanced, so that the holes and electrons recombine in the first emitting layer EML1, and the light-emitting stability of the red light-emitting device R is ensured.

[0069] In another possible implementation, FIG. 5 is a schematic structural diagram of another carrier transport sub-unit provided by an embodiment of the present disclosure. As shown in FIG. 5, the first electron transport sub-unit 312 includes a first hole blocking layer HBL1 and a first electron transport layer ETL1, and the first hole blocking layer HBL1 is closer to the first emitting layer EML1 than the first electron transport layer ETL1. The first electron transport layer ETL1 is mainly used for transporting the electrons generated by the charge generation unit 4 and improving the electron transport efficiency.

[0070] Specifically, the thickness of the first hole blocking layer HBL1 is between 5 nm and 10 nm. The thickness of the first electron transport layer ETL1 is between 5 nm and 30 nm. By thinning the thickness of the first hole blocking layer HBL1 and / or the first electron transport layer ETL1, i.e. shortening the length of the electron transport path, the electron transport rate is improved, and the transport rates of holes and electrons are balanced, so that the holes and electrons recombine in the first emitting layer EML1, and the light-emitting stability of the red light-emitting device R is ensured.

[0071] In some embodiments, as shown in FIG. 4, the charge generation unit 4 comprises an N-type doped charge generation layer N-CGL and a P-type doped charge generation layer P-CGL arranged in sequence in a direction away from the anode 1; the surface of the N-type doped charge generation layer N-CGL in contact with the P-type doped charge generation layer P-CGL is a first surface; the surface of the second light-emitting layer EML2 close to the N-type doped charge generation layer N-CGL is a third surface, and the distance from the third surface to the first surface is a second distance L2. Here, the second distance L2 can be understood as the transmission distance of the holes generated by the charge generation unit 4, i.e., the length of the hole transmission path from the starting point of generation to the second light-emitting layer EML2.

[0072] Alternatively, for the first light-emitting unit 31 on the side of the charge generation unit 4 away from the anode 1, the distance from the surface of the first light-emitting unit 31 close to the N-type doped charge generation layer N-CGL to the first surface also represents the length of the hole transmission path from the starting point of generation to the first light-emitting layer EML1.

[0073] For the convenience of understanding, the present disclosure takes one first light-emitting unit 31 and one second light-emitting unit 32 as an example for illustration, and the case of multiple first light-emitting units 31 is not described in detail.

[0074] The surface of the second light-emitting layer EML2 close to the cathode 2 is a fourth surface, and the shortest distance from the fourth surface to the cathode 2 is a third distance L3, which can be understood as the transmission distance of the electrons generated by the cathode 2, i.e., the length of the electron transmission path from the starting point of generation to the second light-emitting layer EML2.

[0075] Since the materials of the light-emitting layers of different color light-emitting devices are different, the materials of the sub-film layers in the first hole transport sub-unit 311 can be different, and thus the hole mobility corresponding to different color light-emitting devices and the energy level difference between the film layers are different.

[0076] Specifically, as shown in FIG. 4, when the light-emitting device is a red light-emitting device R, the ratio of the second distance R_L2 to the third distance L3 is between 2 and 3.2. For the second light-emitting unit 32 corresponding to the red light-emitting device R, the second distance R_L2 of the hole transmission path and the third distance L3 of the electron transmission path in the second light-emitting unit 32 are adjusted to make the ratio of the second distance R_L2 to the third distance L3 between 2 and 3.2, so as to ensure the transmission balance of the carriers (holes and electrons) in the red light-emitting device R.

[0077] Specifically, as shown in FIG. 4, when the light emitting device is a green light emitting device G, the ratio of the second distance G_L2 to the third distance L3 is between 1.8 and 2.8. The present embodiment adjusts the second distance G_L2 of the hole transport path and the third distance L3 of the electron transport path of the second light emitting unit 32 corresponding to the green light emitting device G in coordination, so that the ratio of the second distance G_L2 to the third distance L3 is between 1.8 and 2.8, thereby ensuring the balance of the transport of the carriers (holes and electrons) in the green light emitting device G.

[0078] Specifically, as shown in FIG. 4, when the light emitting device is a blue light emitting device B, the ratio of the second distance B_L2 to the third distance L3 is between 1.6 and 2.6. The present embodiment adjusts the second distance B_L2 of the hole transport path and the third distance L3 of the electron transport path of the second light emitting unit 32 corresponding to the blue light emitting device B in coordination, so that the ratio of the second distance B_L2 to the third distance L3 is between 1.6 and 2.6, thereby ensuring the balance of the transport of the carriers (holes and electrons) in the blue light emitting device B.

[0079] In a possible implementation, as shown in FIG. 4, when the light emitting device is a red light emitting device R, the second distance R_L2 is between 80 nm and 110 nm. Compared with the prior art (the second distance of the red light emitting device R is less than 80 nm), the present implementation increases the second distance R_L2 of the red light emitting device R, i.e., the length of the hole transport path, to reduce the hole transport rate, thereby balancing the transport rates of the holes and the electrons, making them recombine in the second light emitting layer REML2, and ensuring the light emitting stability of the red light emitting device R.

[0080] Optionally, the second distance R_L2 is 85 nm, 95 nm or 110 nm.

[0081] In a possible implementation, as shown in FIG. 4, when the light emitting device is a green light emitting device G, the second distance G_L2 is between 65 nm and 95 nm. Compared with the prior art (the second distance of the green light emitting device G is about 60 nm), the present implementation increases the second distance G_L2 of the green light emitting device G, i.e., the length of the hole transport path, to reduce the hole transport rate, thereby balancing the transport rates of the holes and the electrons, making them recombine in the second light emitting layer GEML2, and ensuring the light emitting stability of the green light emitting device G.

[0082] Optionally, the second distance G_L2 is 65 nm, 85 nm or 95 nm.

[0083] In a possible implementation, as shown in FIG. 4, when the light-emitting device is a blue light-emitting device B, the second distance B_L2 is between 55 nm and 85 nm. Compared with the prior art (the second distance of the blue light-emitting device B is about 50 nm), this implementation increases the second distance B_L2 of the blue light-emitting device B, i.e., the length of the hole transport path, to reduce the hole transport rate, thereby balancing the transport rates of holes and electrons, making them recombine in the second light-emitting layer BEML2, and ensuring the light-emitting stability of the blue light-emitting device B.

[0084] Optionally, the second distance B_L2 is 55 nm, 70 nm, or 85 nm.

[0085] In some embodiments, as shown in FIG. 4, when the light-emitting device is a red light-emitting device R, the manner of increasing the second distance R_L2 of the red light-emitting device R specifically includes that the thickness of the second hole transport subunit 321 can be set to be between 70 nm and 90 nm, and the thickness of the second hole transport subunit 321 is increased to increase the second distance R_L2 of the red light-emitting device R.

[0086] As shown in FIG. 4, when the light-emitting device is a green light-emitting device G, the manner of increasing the second distance G_L2 of the green light-emitting device G specifically includes that the thickness of the second hole transport subunit 321 can be set to be between 60 nm and 80 nm, and the thickness of the second hole transport subunit 321 is increased to increase the second distance G_L2 of the green light-emitting device G.

[0087] As shown in FIG. 4, when the light-emitting device is a blue light-emitting device B, the manner of increasing the second distance B_L2 of the blue light-emitting device B specifically includes that the thickness of the second hole transport subunit 321 can be set to be between 50 nm and 70 nm, and the thickness of the second hole transport subunit 321 is increased to increase the second distance B_L2 of the blue light-emitting device B.

[0088] In some possible implementations, the second hole transport subunit 321 includes at least one of a second hole transport layer HTL2 and a second electron blocking layer EBL2. For example, as shown in FIGS. 3 and 4, the second hole transport subunit 321 includes, in sequence from the anode 1, the second hole transport layer HTL2 and the second electron blocking layer EBL2. The second hole transport layer HTL2 is mainly used for transporting holes generated by the charge generation unit 4 to improve the hole transport efficiency. The second electron blocking layer EBL2 is mainly used for blocking electrons and transporting holes. As shown in FIG. 5, the second hole transport subunit 321 includes, in sequence from the anode 1, a second hole injection layer HIL2, the second hole transport layer HTL2, and the second electron blocking layer EBL2.

[0089] The transmission rates of holes and electrons can be balanced by increasing the thickness of the second electron blocking layer EBL2 of the light emitting devices of different colors, respectively. And / or, the transmission rates of holes and electrons can be balanced by increasing the thickness of the second hole transport layer HTL2 of the light emitting devices of different colors, respectively.

[0090] For example, as shown in FIG. 4, the thickness of the second hole transport layer HTL2 corresponding to the red light emitting device R, the green light emitting device G and the blue light emitting device B can be the same, for example, 55 nm. The thickness of the second electron blocking layer EBL2 corresponding to the red light emitting device R, the green light emitting device G and the blue light emitting device B is different. For example, the thickness of the second electron blocking layer EBL2 corresponding to the red light emitting device R is greater than the thickness of the second electron blocking layer EBL2 corresponding to the green light emitting device G; and the thickness of the second electron blocking layer EBL2 corresponding to the green light emitting device G is greater than the thickness of the second electron blocking layer EBL2 corresponding to the blue light emitting device B. For example, the thickness of the second electron blocking layer EBL2 corresponding to the red light emitting device R is 30 nm; the thickness of the second electron blocking layer EBL2 corresponding to the green light emitting device G is 20 nm; and the thickness of the second electron blocking layer EBL2 corresponding to the blue light emitting device B is 5 nm.

[0091] In some embodiments, as shown in FIG. 4, the surface of the second light emitting layer EML2 close to the cathode 2 is a fourth surface, and the shortest distance from the fourth surface to the cathode 2 is a third distance L3. The third distance L3 is between 30 nm and 50 nm. In this embodiment, the transmission path length of the electrons generated by the cathode 2 is adjusted, i.e., the third distance L3, to balance the transmission rate of the holes generated by the charge generation unit 4 and the transmission rate of the electrons generated by the cathode 2, so as to realize a high-efficiency and stable tandem light emitting device.

[0092] In a possible implementation, as shown in FIG. 4, the second light emitting unit 32 further includes a second electron transport sub-unit 322 arranged on the side of the second light emitting layer EML2 close to the cathode 2. The thickness of the second electron transport sub-unit 322 is the third distance L3. The second electron transport sub-unit 322 includes, arranged in sequence in the direction away from the cathode 2, an electron injection layer EIL, an electron transport layer ETL and a second hole blocking layer HBL2. The electron injection layer EIL is mainly used to improve the electron injection efficiency, thereby improving the electron transport efficiency. The electron transport layer ETL is mainly used to transport the electrons generated by the cathode 2, so as to improve the electron transport efficiency. The second hole blocking layer HBL2 is mainly used to block holes and transport electrons.

[0093] In a possible implementation, as shown in FIG. 5, the second light-emitting unit 32 further includes a second electron transport sub-unit 322 arranged on the side of the second light-emitting layer EML2 close to the cathode 2. The second electron transport sub-unit 322 includes, in sequence from the direction away from the cathode 2, an electron injection layer EIL, a second electron transport layer ETL2, and a second hole blocking layer HBL2.

[0094] In addition, the present disclosure can also be adjusted by adjusting the hole transport material to select a hole transport material capable of balancing the hole and electron transport efficiency.

[0095] In some embodiments, the first hole transport sub-unit 311 at least includes a first hole transport layer HTL1, and the second hole transport sub-unit 321 at least includes a second hole transport layer HTL2. The structural general formula (I) of the material of the first hole transport layer HTL1 and the material of the second hole transport layer HTL2 is as follows:

[0096] wherein Ar1-Ar3 are each independently selected from any one of hydrogen, deuterium, a nitrile group, a nitro group, a hydroxyl group, a carbonyl group, an ester group, an imide group, an amide group, an alkyl group, a cycloalkyl group, an alkoxy group, an aryloxy group, an alkylthio group, an arylthio group, an alkylsulfonyl group, an arylsulfonyl group, an alkenyl group, a silyl group, a boron group, an amine group, an aryl phosphine group, a phosphine oxide group, an aryl group, and a heteroaryl group; or any adjacent groups among Ar1-Ar3 combine to form a ring; and N represents a nitrogen atom.

[0097] In some embodiments, the first hole transport sub-unit 311 at least includes a first hole transport layer HTL1, and the second hole transport sub-unit 321 at least includes a second hole transport layer HTL2. The structural general formula (II) of the material of the first hole transport layer HTL1 and the material of the second hole transport layer HTL2 is as follows:

[0098] wherein Ar4-Ar7 are each independently selected from any one of hydrogen, deuterium, a nitrile group, a nitro group, a hydroxyl group, a carbonyl group, an ester group, an imide group, an amide group, an alkyl group, a cycloalkyl group, an alkoxy group, an aryloxy group, an alkylthio group, an arylthio group, an alkylsulfonyl group, an arylsulfonyl group, an alkenyl group, a silyl group, a boron group, an amine group, an aryl phosphine group, a phosphine oxide group, an aryl group, and a heteroaryl group; or any adjacent groups among Ar4-Ar7 combine to form a ring; and L represents a substituted or unsubstituted arylene group or a substituted or unsubstituted heteroarylene group.

[0099] In some embodiments, Ar1-Ar7 are selected from any one of the following structures:

[0100] wherein * represents the position of the structural general formula (I) or the position of the structural general formula (II).

[0101] The present embodiments achieve high efficient and stable tandem OLED devices by selecting the materials of the first hole transport layer HTL1 and the second hole transport layer HTL2 with adapted electron transport efficiency to match the electron injection and transport rates.

[0102] In some embodiments, L is selected from any one of the following structures:

[0103] In some embodiments, the cathode 2 and the anode 1 each independently comprise at least one selected from silver (Ag), magnesium (Mg), copper (Cu), aluminum (Al), platinum (Pt), palladium (Pd), gold (Au), nickel (Ni), neodymium (Nd), iridium (Ir), chromium (Cr), lithium (Li), calcium (Ca), lithium fluoride / calcium (LiF / Ca), lithium fluoride / aluminum (LiF / Al), molybdenum (Mo), titanium (Ti), indium (In), tin (Sn), zinc (Zn), and ytterbium (Yb), or an oxide thereof. For example, when the light emitting device is a top emission structure device, the anode 1 is an electrode with reflectivity and the cathode 2 is an electrode with transmissivity or semi-transmissivity. For example, the anode 1 is selected from a material with high work function, such as an ITO / Ag / ITO stack structure; and the cathode 2 is selected from a material with low work function, which can be a semi-transmissive metal or metal alloy material, such as an Ag / Mg alloy material.

[0104] In some embodiments, the material of the hole injection layer (e.g., the first hole injection layer HIL1 and the second hole injection layer HIL2) can include, but is not limited to, a combination of a p-type dopant of a strong electron-withdrawing system and a hole-transporting material doped together. Among them, the p-type dopant can include a combination of any one or more of 2,3,6,7,10,11-hexacyano-1,4,5,8,9,12-hexaazatriphenylene, 2,3,5,6-tetrafluoro-7,7',8,8'-tetracyano-p- benzoquinone (F4TCNQ), 1,2,3-tris[(cyano)(4-cyano-2,3,5,6-tetrafluorophenyl)methylene] cyclopropane. The hole-transporting material can include a combination of any one or more of arylamine hole-transporting materials, dimethylfluorene hole-transporting materials, carbazole hole-transporting materials. For example, the hole-transporting material can include a combination of any one or more of 4,4'-bis[N-(1-naphthyl)-N-phenylamino]biphenyl (NPB), N,N'-bis(3-methylphenyl)-N,N'-diphenyl-[1,1'-biphenyl]-4,4'-diamine (TPD), 4-phenyl-4'-(9-phenylfluoren-9-yl)triphenylamine (BAFLP), 4,4'-bis[N-(9,9-dimethylfluoren-2-yl)-N-phenylamino]biphenyl (DFLDPBi), 4,4'-di(9-carbazolyl) biphenyl (CBP), and 9-phenyl-3-[4-(10-phenyl-9-anthryl)phenyl]-9H-carbazole (PCzPA).

[0105] In some embodiments, the material of the electron blocking layer (e.g., the first electron blocking layer EBL1 and the second electron blocking layer EBL2) can include, but is not limited to, a combination of any one or more of arylamine electron blocking materials, dimethylfluorene electron blocking materials, carbazole electron blocking materials. For example, the material of the electron blocking layer can include a combination of any one or more of 4,4'-bis[N-(1-naphthyl)-N-phenylamino]biphenyl (NPB), N,N'-bis(3-methylphenyl)-N,N'-diphenyl-[1,1'-biphenyl]-4,4'-diamine (TPD), 4-phenyl-4'-(9-phenylfluoren-9-yl)triphenylamine (BAFLP), 4,4'-bis[N-(9,9-dimethylfluoren-2-yl)-N-phenylamino]biphenyl (DFLDPBi), 4,4'-di(9-carbazolyl) biphenyl (CBP), and 9-phenyl-3-[4-(10-phenyl-9-anthryl)phenyl]-9H-carbazole (PCzPA).

[0106] In some embodiments, the material of the light-emitting layer (e.g., the first light-emitting layer EML1 and the second light-emitting layer EML2) can include one light-emitting material, or two or more light-emitting materials. For example, the material of the light-emitting layer (e.g., the first light-emitting layer EML1 and the second light-emitting layer EML2) can include a host light-emitting material and a guest light-emitting material doped into the host light-emitting material; the material of the light-emitting layer can include a light-emitting material having a thermally activated delayed fluorescence characteristic at room temperature, a light-emitting material having a fluorescence characteristic at room temperature, a light-emitting material having a phosphorescence characteristic at room temperature.

[0107] For example, when the light-emitting device is a red light-emitting device R, the material of the first light-emitting layer EML1 is a red light-emitting material, which can specifically include a combination of any one or more of a DCM-based red light-emitting material and a metal complex-based red light-emitting material. For example, the red light-emitting material can include a combination of any one or more of 4-(dicyanomethylene)-2-methyl-6-(4-dimethylaminostyryl)-4H-pyran (DCM), 4-(dicyanomethylene)-2-tert-butyl-6-(1,1,7,7-tetramethylguercin-9-enyl)-4H-pyran (DCJTB), bis(1-phenylisoquinoline)(acetylacetone)iridium(III) (Ir(piq)2(acac)), octaethylporphyrin platinum (abbreviated as: PtOEP), bis(2-(2'-benzothienyl)pyridine-N,C3')(acetylacetone)iridium (abbreviated as: Ir(btp)2(acac).

[0108] For example, when the light-emitting device is a green light-emitting device G, the material of the first light-emitting layer EML1 is a green light-emitting material, which can specifically include a combination of any one or more of a coumarin dye, a quinacridone copper derivative-based green light-emitting material, a polycyclic aromatic hydrocarbon-based green light-emitting material, a diamine anthracene derivative-based green light-emitting material, a carbazole derivative-based green light-emitting material, and a metal complex-based green light-emitting material. For example, the green light-emitting material can include a combination of any one or more of coumarin 6 (C-6), coumarin 545T (C-525T), quinacridone copper (QA), N,N'-dimethylquinacridone (DMQA), 5,12-diphenyl naphthacene (DPT), N10,N10'-diphenyl-N10,N10'-dibenzoyl-9,9'-dianthracene-10,10'-diamine (abbreviated as: BA-NPB), tris(8-hydroxyquinoline)aluminum(III) (abbreviated as: Alq3), tris(2-phenylpyridine)iridium (Ir(ppy)3), bis(2-phenylpyridine)iridium (Ir(ppy)2(acac)).

[0109] Exemplarily, when the light-emitting device is a blue light-emitting device B, the material of the first light-emitting layer EML1 is a blue light-emitting material, which can specifically include any one or a combination of more than one of a pyrene derivative blue light-emitting material, an anthracene derivative blue light-emitting material, a fluorene derivative blue light-emitting material, a perylene derivative blue light-emitting material, a styrylamine derivative blue light-emitting material, and a metal complex blue light-emitting material. For example, the blue light-emitting material can include a combination of any one or more of N1,N6-di([1,1’-biphenyl]-2-yl)-N1,N6-di([1,1’-biphenyl]-4-yl)pyrene-1,6-diamine, 9,10-di-(2-naphthyl)anthracene (ADN), 2-methyl-9,10-di-2-naphthylanthracene (MADN), 2,5,8,11-tetra-tert-butyl perylene (TBPe), 4,4’-bis[4-(diphenylamino)styryl]biphenyl (BDAVBi), 4,4’-bis[4-(dipara-tolylamino)styryl]biphenyl (DPAVBi), bis(4,6-difluorophenylpyridine-C2,N)picolinate iridium (FIrpic).

[0110] In some embodiments, the material of the hole blocking layer (e.g., the first hole blocking layer HBL1 and the second hole blocking layer HBL2) can include, but is not limited to, an aromatic heterocyclic hole blocking material. Specifically, the material of the hole blocking layer (e.g., the first hole blocking layer HBL1 and the second hole blocking layer HBL2) can include any one or more of a combination of a benzimidazole and its derivative hole blocking material, an imidazopyridine and its derivative hole blocking material, a benzimidazophenanthroline derivative hole blocking material, a pyrimidine and its derivative hole blocking material, a triazine derivative hole blocking material, a pyridine and its derivative hole blocking material, a pyrazine and its derivative hole blocking material, a quinoxaline and its derivative hole blocking material, an oxadiazole and its derivative hole blocking material, a quinoline and its derivative hole blocking material, an isoquinoline derivative hole blocking material, a phenanthroline derivative hole blocking material, a diazaphosphole hole blocking material, a phosphine oxide hole blocking material, an aromatic ketone hole blocking material, a lactam, a borane hole blocking material. For example, the material of the hole blocking layer can include a combination of any one or more of 2-(4-biphenyl)-5-(4-tert-butylphenyl)-1,3,4-oxadiazole (PBD), 1,3-bis[5-(p-tert-butylphenyl)-1,3,4-oxadiazol-2-yl]benzene (OXD-7), 3-(4-tert-butylphenyl)-4-phenyl-5-(4-biphenylyl)-1,2,4-triazole (TAZ), 3-(4-tert-butylphenyl)-4-(4-ethylphenyl)-5-(4-biphenylyl)-1,2,4-triazole (p-EtTAZ), bathophenanthroline (BPhen), 2,6-bis(3'-carbazolyl)pyridine (BCP), 4,4'-bis(5-methylbenzoxazol-2-yl)stilbene (BzOs).

[0111] In some embodiments, the material of the electron transport layer ETL (or the first electron transport layer ETL1 and the second electron transport layer ETL2) includes, but is not limited to, a benzimidazole derivative, an imidazopyridine derivative, a benzimidazophenanthroline derivative, and the like imidazole derivative; a pyrimidine derivative, a triazine derivative, and the like oxazine derivative; a quinoline derivative, an isoquinoline derivative, a phenanthroline derivative, and the like compound containing a nitrogen-containing six-membered ring structure (also including a compound having a phosphine oxide group as a substituent on a heterocycle, such as OXD-7, TAZ, p-EtTAZ), BPhen, BCP, and the like.

[0112] In some embodiments, the material of the electron injection layer EIL includes, but is not limited to, a compound of one or more of Li, Yb, Mg, Ca.

[0113] For the convenience of understanding, the materials of the various film layers in the light-emitting device are listed and described below with one specific example.

[0114] The hole injection layer (e.g. the first hole injection layer HIL1 and the second hole injection layer HIL2) and the P-type doped charge generation layer P-CGL both comprise a hole injection material HIL' and a hole transport material HTL' doped together, wherein the hole injection material HIL' has a molecular structure of:

[0115] The hole transport material HTL' has a molecular structure of:

[0116] The electron blocking layer (the first electron blocking layer REBL1 and the second electron blocking layer REBL2) corresponding to the red light emitting device R has a material molecular structure of:

[0117] The electron blocking layer (the first electron blocking layer GEBL1 and the second electron blocking layer GEBL2) corresponding to the green light emitting device G has a material molecular structure of:

[0118] The electron blocking layer (the first electron blocking layer BEBL1 and the second electron blocking layer BEBL2) corresponding to the blue light emitting device B has a material molecular structure of:

[0119] The light emitting layer (the first light emitting layer REML1 and the second light emitting layer REML2) corresponding to the red light emitting device R has a material comprising a host material (RH) and a guest material (RD), wherein the host material (RH) comprises a P-type doped host material (RH_P) and an N-type doped host material (RH_N). Wherein, the P-type doped host material (RH_P) has a molecular structure of:

[0120] The N-type doped host material (RH_N) has a molecular structure of:

[0121] The guest material (RD) has a molecular structure of

[0122] For example, the doping mass ratio of the P-type doped host material (RH_P) and the N-type doped host material (RH_N) is 1:1.

[0123] The light emitting layer (the first light emitting layer GEML1 and the second light emitting layer GEML2) corresponding to the green light emitting device G has a material comprising a host material (GH) and a guest material (GD), wherein the host material (GH) comprises a P-type doped host material (GH_P) and an N-type doped host material (GH_N). Wherein, the P-type doped host material (GH_P) has a molecular structure of:

[0124] The molecular structure of the N-doped host material (GH_N) is as follows:

[0125] The molecular structure of the guest material (GD) is as follows:

[0126] For example, the mass ratio of the P-doped host material (GH_P) and the N-doped host material (GH_N) is 1:1.

[0127] The materials of the light-emitting layer (the first light-emitting layer BEML1 and the second light-emitting layer BEML2) corresponding to the blue light-emitting device B include a host material (BH) and a guest material (BD). The molecular structure of the host material (BH) is as follows:

[0128] The molecular structure of the guest material (BD) is as follows:

[0129] The molecular structure of the material of the N-doped charge generation layer N-CGL is as follows:

[0130] The molecular structure of the material of the hole blocking layer (for example, the first hole blocking layer HBL1 and the second hole blocking layer HBL2) is as follows:

[0131] The material of the electron transport layer ETL (or the first electron transport layer ETL1 and the second electron transport layer ETL2) includes an electron transport material ETL' and Liq doped together. The molecular structure of the electron transport material ETL' is as follows:

[0132] The molecular structure of Liq is as follows:

[0133] For example, the mass ratio of the electron transport material ETL' and Liq doped together in the electron transport layer ETL is 1:1.

[0134] The above is a detailed description of the structure and materials of the light-emitting device.

[0135] For the light-emitting device formed by each of the above embodiments and combinations thereof, the intercalation method is used to randomly select and verify the light-emitting device in some embodiments to verify the effect of the improved structure of the light-emitting device. It is proved that by increasing the thickness of the first hole transport subunit 311 and / or the second hole transport subunit 321, the transmission rate of the carrier can be effectively balanced, and the high efficiency and stability of the series light-emitting device are ensured.

[0136] The device structure of the intercalation method, a verification light-emitting layer different from the light-emitting color of the first light-emitting layer EML1 is inserted in the individual light-emitting device. If the verification light-emitting layer emits light, it indicates that the carrier recombination center deviates from the first light-emitting layer EML1, and the recombination occurs at the verification light-emitting layer, which affects the light-emitting efficiency and the service life of the light-emitting device. If the verification light-emitting layer does not emit light, it indicates that the carrier recombination center does not deviate from the first light-emitting layer EML1, and the recombination occurs at the first light-emitting layer EML1, which does not affect the light-emitting efficiency of the light-emitting device.

[0137] Comparative Example 1: The device structure of the red light-emitting device R, ITO→HTL’:HIL’, 97:3, 10 nm→HTL1, 20 nm→REBL1, 35 nm→REML1(RH:RD, 5%), 40 nm→verification light-emitting layer EML1(GH:GD, 10%), 3 nm→HBL1, 5 nm→N-CGL(CGL:Li, 1%), 20 nm→P-CGL(HTL’:HIL’, 90:10), 10 nm→HTL2, 35 nm→REBL2, 35 nm→REML2(RH:RD, 5%), 40 nm→verification light-emitting layer EML2(GH:GD, 10%), 3 nm→HBL2, 5 nm→ETL’:Liq, 1:1, 30 nm→Yb, 1 nm→Mg:Ag, 13 nm→CPL, 60 nm.

[0138] Example 1: The device structure of the red light-emitting device R, ITO→HTL’:HIL’, 97:3, 10 nm→HTL1, 100 nm→REBL1, 90 nm→REML1(RH:RD, 5%), 40 nm→verification light-emitting layer EML1(GH:GD, 10%), 3 nm→HBL1, 5 nm→N-CGL(CGL:Li, 1%), 20 nm→P-CGL(HTL’:HIL’, 90:10), 10 nm→HTL2, 55 nm→REBL2, 30 nm→REML2(RH:RD, 5%), 40 nm→verification light-emitting layer EML2(GH:GD, 10%), 3 nm→HBL2, 5 nm→ETL’:Liq, 1:1, 30 nm→Yb, 1 nm→Mg:Ag, 13 nm→CPL, 60 nm.

[0139] Comparative Example 2: Device structure of green light emitting device G, ITO→HTL':HIL', 97:3, 10 nm→HTL1, 20 nm→GEBL1, 15 nm→GEML1(GH:GD, 10%), 30 nm→validation emitting layer EML1(RH:RD, 10%), 3 nm→HBL1, 5 nm→N-CGL(CGL:Li, 1%), 20 nm→P-CGL(HTL':HIL', 90:10), 10 nm→HTL2, 35 nm→GEBL2, 15 nm→GEML2(GH:GD, 10%), 30 nm→validation emitting layer EML2(RH:RD, 10%), 3 nm→HBL2, 5 nm→ETL':Liq, 1:1, 30 nm→Yb, 1 nm→Mg:Ag, 13 nm→CPL, 60 nm.

[0140] Example 2: Device structure of green light emitting device G, ITO→HTL':HIL', 97:3, 10 nm→HTL1, 100 nm→GEBL1, 40 nm→GEML1(GH:GD, 10%), 30 nm→validation emitting layer EML1(RH:RD, 10%), 3 nm→HBL1, 5 nm→N-CGL(CGL:Li, 1%), 20 nm→P-CGL(HTL':HIL', 90:10), 10 nm→HTL2, 55 nm→GEBL2, 20 nm→GEML2(GH:GD, 10%), 30 nm→validation emitting layer EML2(RH:RD, 10%), 3 nm→HBL2, 5 nm→ETL':Liq, 1:1, 30 nm→Yb, 1 nm→Mg:Ag, 13 nm→CPL, 60 nm.

[0141] Comparative Example 3: Device structure of blue light emitting device B, ITO→HTL':HIL', 97:3, 10 nm→HTL1, 20 nm→BEBL1, 5 nm→BEML1(BH:BD, 2%), 7 nm→validation emitting layer EML1(RH:RD, 10%), 3 nm→HBL1, 5 nm→N-CGL(CGL:Li, 1%), 20 nm→P-CGL(HTL':HIL', 90:10), 10 nm→HTL2, 35 nm→BEBL2, 5 nm→BEML2(BH:BD, 2%), 7 nm→validation emitting layer EML2(RH:RD, 10%), 3 nm→HBL2, 5 nm→ETL':Liq, 1:1, 30 nm→Yb, 1 nm→Mg:Ag, 13 nm→CPL, 60 nm.

[0142] Example 3: Device structure of blue light-emitting device B, ITO→HTL’:HIL’, 97:3, 10 nm→HTL1, 100 nm→BEBL1, 5 nm→BEML1(BH:BD, 2%), 7 nm→validation emitting layer EML1(RH:RD, 10%), 3 nm→HBL1, 5 nm→N-CGL(CGL:Li, 1%), 20 nm→P-CGL(HTL’:HIL’, 90:10), 10 nm→HTL2, 55 nm→BEBL2, 5 nm→BEML2(BH:BD, 2%), 7 nm→validation emitting layer EML2(RH:RD, 10%), 3 nm→HBL2, 5 nm→ETL’:Liq, 1:1, 30 nm→Yb, 1 nm→Mg:Ag, 13 nm→CPL, 60 nm.

[0143] It should be noted that in the above Comparative Examples 1-3 and Examples 1-3, “→” refers to the order from the anode to the cathode to the light extraction layer CPL (such as the light extraction layer CPL shown in FIG. 6 arranged on the side of the cathode 2 away from the anode 1). The front and back of “→” respectively represent different film layer structures. “ITO” represents the anode 1, wherein the anode 1 is made of ITO material (indium tin oxide material). “HTL’:HIL’, 97:3, 10 nm” represents that the HTL’ material and the HIL’ material are doped to form the first hole injection layer HIL1, the mass doping ratio of the HTL’ material and the HIL’ material is 97:3, and the thickness of the first hole injection layer HIL1 is 10 nm. “RH:RD, 10%” represents that the RH material and the RD material are doped, and 10% represents that the mass doping concentration of the RD material is 10%, that is, the ratio of the mass of the RD material to the sum of the mass of the RH material and the mass of the RD material. “ETL’:Liq, 1:1, 30 nm” represents that the ETL’ material and the Liq material are doped to form the second electron transport layer ETL2, the mass doping ratio of the ETL’ material and the Liq material is 1:1, and the thickness of the second electron transport layer ETL2 is 30 nm. “Yb, 1 nm” represents the electron injection layer EIL, wherein the electron injection layer EIL is made of Yb, and the thickness of the electron injection layer EIL is 1 nm. “Mg:Ag, 13 nm” represents the cathode 2, wherein the cathode 2 is made of Mg:Ag, and the thickness of the cathode 2 is 13 nm. “CPL, 60 nm” represents the light extraction layer CPL (such as the light extraction layer CPL shown in FIG. 6 arranged on the side of the cathode 2 away from the anode 1), wherein the thickness of the light extraction layer CPL is 60 nm. Similar parameter structures represent the same, and the repeated parts will not be described again.

[0144] The film layer materials of Comparative Examples 1-3 and Example 1-3 above can be selected from any combination of the above-mentioned materials. The film layer materials of Comparative Example 1 and Example 1 are the same. The film layer materials of Comparative Example 2 and Example 2 are the same. The film layer materials of Comparative Example 3 and Example 3 are the same.

[0145] The comparative analysis of Comparative Examples 1-3 and Examples 1-3 above is shown in Table 1.

[0146] Table 1

[0147] The luminescent devices of Comparative Examples 1-3 and Examples 1-3 above were measured under a current density of 15 mA / cm 2 and the device spectrum data obtained is shown in Table 2.

[0148] Table 2

[0149] In the intercalation method experiment, the luminescent layer of Comparative Examples 1-3 emits light, indicating that the carrier imbalance of the luminescent device corresponding to Comparative Examples 1-3 is consistent with the case where the center deviates from the first luminescent layer EML1. In the luminescent device consistent with the thickness relationship of the present disclosure, the luminescent layer does not emit light, indicating that the luminescent device provided by the present disclosure can effectively improve the carrier balance in the luminescent device and is beneficial to improving the performance of the device.

[0150] For the luminescent devices of each of the above embodiments and combinations thereof, the following Comparative Example 4 and a plurality of Examples 4-13 are provided, wherein the luminescent devices in Comparative Example 4 and a plurality of Examples 4-13 include different hole transport materials, and the effects of the luminescent devices provided with different materials are verified.

[0151] In combination with Table 3 and Table 4, Table 3 shows the hole transport materials corresponding to structural formula (I) and structural formula (II), respectively, and Table 4 shows the device voltage, luminous efficiency (EQE) of the luminescent devices of Comparative Example 4 and Examples 4-13 under a current density of 15 mA / cm 2 and the device lifetime (LT95@1000nit) of the luminescent devices of Comparative Example 4 and Examples 4-13 under a brightness of 1000 nit.

[0152] The performance of the luminescent devices in Comparative Example 4 and a plurality of Examples 4-13 including different hole transport materials in terms of voltage, EQE, and lifetime (LT95@1000nit).

[0153] The molecular structure of the material of the hole transport layer of the luminescent device of Comparative Example 4 (e.g., the hole transport material HTL shown in Table 4) is as follows:

[0154] As described above, the first hole transport sub-unit 311 includes at least a first hole transport layer HTL1; the second hole transport sub-unit 321 includes at least a second hole transport layer HTL2; the structural formulas (one) and (two) of the material of the first hole transport layer HTL1 and the material of the second hole transport layer HTL2 are as follows, respectively:

[0155] Structural formula (one):

[0156] Structural formula (two):

[0157] In some embodiments, Ar1-Ar7 are selected from any one of the structures with the following labels:

[0158] Wherein, * represents the position of the structural formula (one) or the position of the structural formula (two).

[0159] In some embodiments, L is selected from any one of the structures with the following labels:

[0160] The material of the hole transport layer of the light emitting device of Example 4 is selected as compound 1, i.e., in Example 4, the hole transport material corresponds to the above structural general formula (I). Specifically, the material of the hole transport layer is compound 1, which has the above structural general formula (I), wherein Ar1, Ar2, Ar3 have the structures of the above label 1, label 1, and label 17, respectively. In Example 4, the voltage of the light emitting device including the hole transport material of compound 1 is 98%, the EQE is 109%, and the lifetime is 111%. Similarly, the material of the hole transport layer of the light emitting device of Example 5 is selected as compound 2. Specifically, in Example 5, the material of the hole transport layer is compound 2, which has the above structural general formula (I), wherein Ar1, Ar2, Ar3 have the structures of the above label 2, label 2, and label 21, respectively. In Example 5, the voltage of the light emitting device including the hole transport material of compound 2 is 97%, the EQE is 104%, and the lifetime is 116%. The material of the hole transport layer of the light emitting device of Example 6 is selected as compound 3; the material of the hole transport layer of the light emitting device of Example 7 is selected as compound 4; the material of the hole transport layer of the light emitting device of Example 8 is selected as compound 5; the material of the hole transport layer of the light emitting device of Example 9 is selected as compound 6, i.e., in Example 9, the hole transport material corresponds to the above structural general formula (II). Specifically, the material of the hole transport layer is compound 6, which has the above structural general formula (II), wherein Ar1, Ar2, L, Ar3, Ar4 have the structures of the above label 2, label 3, label D, label 4, and label 1, respectively. In Example 9, the voltage of the light emitting device including the hole transport material of compound 6 is 99%, the EQE is 105%, and the lifetime is 105%. Similarly, the material of the hole transport layer of the light emitting device of Example 10 is selected as compound 7; the material of the hole transport layer of the light emitting device of Example 11 is selected as compound 8; the material of the hole transport layer of the light emitting device of Example 12 is selected as compound 9; the material of the hole transport layer of the light emitting device of Example 13 is selected as compound 10. The material selection of the above compounds 1-10 is shown in Table 3, and the corresponding performance of the light emitting device is shown in Table 4.

[0161] Table 3

[0162] Table 4

[0163] As can be seen from Table 4, the selection of the material of the hole transport layer (the first hole transport layer HTL1 and the second hole transport layer HTL2) of the present disclosure, combined with the actual film thickness, can realize a higher efficiency and lifetime of the tandem device.

[0164] In addition, the display panel provided by the embodiments of the present disclosure comprises a plurality of light-emitting devices of different colors as described above and their combinations, so that the tandem light-emitting device can realize high-efficiency and stable full-color display. The tandem light-emitting device is, for example, a Tandem OLED device.

[0165] In some embodiments, FIG. 6 is a schematic diagram of a display panel provided by the embodiments of the present disclosure. As shown in FIG. 6, the plurality of light-emitting devices of different colors comprises a red light-emitting device R, a green light-emitting device G, and a blue light-emitting device B; the materials of the first electron blocking layers EBL1 corresponding to the red light-emitting device R, the green light-emitting device G, and the blue light-emitting device B are different; the materials of the second electron blocking layers EBL2 corresponding to the red light-emitting device R, the green light-emitting device G, and the blue light-emitting device B are different; the materials of the first light-emitting layers EML1 corresponding to the red light-emitting device R, the green light-emitting device G, and the blue light-emitting device B are different; and the materials of the second light-emitting layers EML2 corresponding to the red light-emitting device R, the green light-emitting device G, and the blue light-emitting device B are different.

[0166] In some embodiments, the light-emitting device mainly comprises an anode 1, a cathode 2, a plurality of light-emitting units arranged between the anode 1 and the cathode 2, and a charge generation unit 4 arranged between adjacent light-emitting units. At least one first light-emitting unit 31 and one second light-emitting unit 32 are included in the plurality of light-emitting units, and the first light-emitting unit 31 is closer to the anode 1 than the second light-emitting unit 32. The first light-emitting unit 31 comprises a first light-emitting layer EML1 and a first hole transport sub-unit 311 arranged on a side of the first light-emitting layer EML1 close to the anode 1; the second light-emitting unit 32 comprises a second light-emitting layer EML2 and a second hole transport sub-unit 321 arranged on a side of the second light-emitting layer EML2 close to the anode 1. The charge generation unit 4 comprises an N-type doped charge generation layer N-CGL and a P-type doped charge generation layer P-CGL arranged in sequence away from the anode 1; a surface of the N-type doped charge generation layer N-CGL and the P-type doped charge generation layer P-CGL in contact is a first surface; a surface of the first light-emitting layer EML1 close to the N-type doped charge generation layer N-CGL is a second surface, and a distance between the first surface and the second surface is a first distance L1.

[0167] For the red light-emitting device R, a ratio of the thickness R_H of the first hole transport sub-unit 311 to the first distance L1 is between 6 and 10. For the green light-emitting device G, a ratio of the thickness G_H of the first hole transport sub-unit 311 to the first distance L1 is between 5 and 8. For the blue light-emitting device B, a ratio of the thickness B_H of the first hole transport sub-unit 311 to the first distance L1 is between 4 and 6.

[0168] The embodiment adjusts the distance of the hole transport path and the distance of the electron transport path in the first light emitting unit 31 of each color light emitting device, so as to ensure the transport balance of the carriers (holes and electrons) in each color light emitting device.

[0169] In some embodiments, the thickness R_H of the first hole transport sub-unit 311 of the red light emitting device R is between 170 nm and 230 nm. The thickness G_H of the first hole transport sub-unit 311 of the green light emitting device G is between 130 nm and 170 nm. The thickness B_H of the first hole transport sub-unit 311 of the blue light emitting device B is between 90 nm and 130 nm.

[0170] The embodiment increases the length of the hole transport path of each color light emitting device, so as to reduce the hole transport rate, balance the transport rates of the holes and the electrons, and make the holes and the electrons recombine in the corresponding first light emitting layer EML1, so as to ensure the light emitting stability of each color light emitting device.

[0171] In some embodiments, the first distance is between 15 nm and 30 nm. The embodiment adjusts the first distance L1, i.e., the length of the transport path of the electrons generated by the charge generation unit 4, so as to balance the transport rate of the holes generated by the anode 1 and the transport rate of the electrons generated by the charge generation unit 4, and realize efficient and stable series light emitting device.

[0172] In some embodiments, the charge generation unit 4 comprises an N-type doped charge generation layer N-CGL and a P-type doped charge generation layer P-CGL arranged in sequence away from the anode 1; the surface of the N-type doped charge generation layer N-CGL and the P-type doped charge generation layer P-CGL in contact is a first surface; the surface of the second light emitting layer EML2 close to the N-type doped charge generation layer N-CGL is a third surface, and the distance from the third surface to the first surface closest to it is a second distance L2. The surface of the second light emitting layer EML2 close to the cathode 2 is a fourth surface, and the shortest distance from the fourth surface to the cathode 2 is a third distance L3.

[0173] For the red light emitting device R, the ratio of the second distance R_L2 to the third distance L3 is between 2 and 3.2. For the green light emitting device G, the ratio of the second distance G_L2 to the third distance L3 is between 1.8 and 2.8. For the blue light emitting device B, the ratio of the second distance B_L2 to the third distance L3 is between 1.6 and 2.6.

[0174] The embodiment adjusts the second distance L2 of the hole transport path and the third distance L3 of the electron transport path in the second light emitting unit 32 of each color light emitting device, so as to ensure the transport balance of the carriers (holes and electrons) in each color light emitting device.

[0175] In some embodiments, for the red light emitting device R, the second distance R_L2 is between 80 nm and 110 nm. For the green light emitting device G, the second distance G_L2 is between 65 nm and 95 nm. For the blue light emitting device B, the second distance B_L2 is between 55 nm and 85 nm.

[0176] The present embodiment balances the transport rates of holes and electrons by increasing the length of the hole transport path of the light emitting device of each color, so that the holes and electrons recombine in the first light emitting layer EML1, thereby ensuring the light emitting stability of the light emitting device.

[0177] In some embodiments, for the red light emitting device R, the thickness of the second hole transport sub-unit 321 is between 70 nm and 90 nm; for the green light emitting device G, the thickness of the second hole transport sub-unit 321 is between 60 nm and 80 nm; for the blue light emitting device B, the thickness of the second hole transport sub-unit 321 is between 50 nm and 70 nm.

[0178] The present embodiment balances the transport rates of holes and electrons by increasing the thickness of the second hole transport sub-unit 321 of the light emitting device of each color, so as to increase the second distance of the light emitting device of each color, i.e. to increase the length of the hole transport path.

[0179] In some embodiments, as shown in FIG. 6, the multiple light emitting devices of different colors share the same first hole injection layer HIL1, first hole transport layer HTL1, first hole blocking layer HBL1, charge generation unit 4, second hole transport layer HTL2, second hole blocking layer HBL2, electron transport layer ETL, electron injection layer EIL and cathode 2.

[0180] Here, the term “share” means that the materials and thicknesses of the film layers are the same. That is, the materials and thicknesses of the first hole injection layer HIL1 of the light emitting devices of different colors are the same; the materials and thicknesses of the first hole transport layer HTL1 of the light emitting devices of different colors are the same; the materials and thicknesses of the first hole blocking layer HBL1 of the light emitting devices of different colors are the same; the materials and thicknesses of the charge generation unit 4 of the light emitting devices of different colors are the same; the materials and thicknesses of the second hole transport layer HTL2 of the light emitting devices of different colors are the same; the materials and thicknesses of the second hole blocking layer HBL2 of the light emitting devices of different colors are the same; the materials and thicknesses of the electron transport layer ETL of the light emitting devices of different colors are the same; the materials and thicknesses of the electron injection layer EIL of the light emitting devices of different colors are the same; the materials and thicknesses of the cathode 2 of the light emitting devices of different colors are the same.

[0181] In some embodiments, the first hole injection layer HIL1 of the light emitting device of different colors can be formed as an integral structure, i.e., the first hole injection layer HIL1 is provided as an integral layer. In some embodiments, the first hole transport layer HTL1 of the light emitting device of different colors can be formed as an integral structure, i.e., the first hole transport layer HTL1 is provided as an integral layer.

[0182] In some embodiments, as shown in FIG. 6, the display panel further comprises a light extraction layer CPL provided on the side of the cathode 2 away from the anode 1.

[0183] The molecular structure of the material of the light extraction layer CPL is as follows:

[0184] Exemplarily, the thickness of the light extraction layer CPL is between 55 nm and 65 nm.

[0185] In some embodiments, the display panel further comprises an encapsulation layer 5 provided on the side of the light extraction layer CPL away from the cathode 2. The encapsulation layer 5 can be a single-layer structure or a combination of multiple-layer structures. Exemplarily, when the encapsulation layer 5 is a multiple-layer structure, it can comprise a first inorganic material layer, an organic material layer, and a second inorganic material layer provided in sequence in the direction away from the cathode 2.

[0186] In addition, the embodiments of the present disclosure also provide a preparation method of a display panel, which specifically comprises the following steps S1-S16.

[0187] S1, ultrasonic treatment is performed on a glass plate with indium tin oxide (ITO) in a cleaning agent, the glass plate after ultrasonic treatment is washed in deionized water, then ultrasonic oil removal is performed in an acetone-ethanol mixed solvent, and then baking is performed in a clean environment until the water is completely removed, to form an anode 1 of a light emitting device.

[0188] S2, the glass plate with the anode 1 in the above step S1 is placed in a vacuum chamber, vacuum is extracted to 1×10 -5 ~1×10 -6 Pa, hole injection material HIL' and hole transport material HTL' are vacuum evaporated on the anode 1 in a doping mass ratio of 97:3, and the thickness of the material is 10 nm, to form a first hole injection layer HIL1.

[0189] S3, hole transport material is evaporated on the side of the first hole injection layer HIL1 away from the anode 1, to form a first hole transport layer HTL1. The thickness of the first hole transport layer HTL1 is 100 nm.

[0190] S4, evaporate electron blocking material on the side of the first hole transport layer HTL1 away from the first hole injection layer HIL1 to form the first electron blocking layer EBL1. The material and thickness of the first electron blocking layer EBL1 are different for different color light emitting devices.

[0191] S5, evaporate light emitting material on the side of the first electron blocking layer EBL1 away from the first hole transport layer HTL1 to form the first light emitting layer EML1. The first light emitting layer EML1 includes host material and guest material, which can be prepared by multi-source co-evaporation method. The host material, guest material and thickness are different in different color light emitting devices.

[0192] S6, evaporate hole blocking material on the side of the first light emitting layer EML1 away from the first electron blocking layer EBL1 to form the first hole blocking layer HBL1. The thickness of the first hole blocking layer HBL1 is 5 nm.

[0193] S7, form N-type doped charge generation layer N-CGL on the side of the first hole blocking layer HBL1 away from the first light emitting layer EML1 by multi-source co-evaporation method. The material of the N-type doped charge generation layer N-CGL is doped by multiple materials, such as CGL:Li with a mass ratio of 9:1. The N-type doped charge generation layer N-CGL can be prepared by multi-source co-evaporation method. The thickness of the N-type doped charge generation layer N-CGL is 20 nm.

[0194] S8, form P-type doped charge generation layer P-CGL on the side of the N-type doped charge generation layer N-CGL away from the first hole blocking layer HBL1 by multi-source co-evaporation method. The material of the P-type doped charge generation layer P-CGL includes hole injection material doped in hole transport material with a mass fraction of 10%. The P-type doped charge generation layer P-CGL can be prepared by multi-source co-evaporation method. The thickness of the P-type doped charge generation layer P-CGL is 10 nm.

[0195] S9, evaporate hole transport material on the side of the P-type doped charge generation layer P-CGL away from the N-type doped charge generation layer N-CGL to form the second hole transport layer HTL2. The thickness of the second hole transport layer HTL2 is 55 nm.

[0196] S10, evaporate electron blocking material on the side of the second hole transport layer HTL2 away from the P-type doped charge generation layer P-CGL to form the second electron blocking layer EBL2. The material and thickness of the second electron blocking layer EBL2 are different for different color light emitting devices.

[0197] S11, forming an evaporation light emitting material on the side of the second electron blocking layer EBL2 away from the second hole transport layer HTL2 to form a second light emitting layer EML2. The second light emitting layer EML2 includes a host material and a guest material, and can be prepared by a multi-source co-evaporation method. In different color light emitting devices, the host material, the guest material and the thickness are different.

[0198] S12, evaporating a hole blocking material on the side of the second light emitting layer EML2 away from the second electron blocking layer EBL2 to form a second hole blocking layer HBL2. The thickness of the second hole blocking layer HBL2 is 5 nm.

[0199] S13, forming an electron transport layer ETL on the side of the second hole blocking layer HBL2 away from the second light emitting layer EML2. The material of the electron transport layer ETL includes an electron transport material and Liq doped together, and the mass ratio of the two is 1:1. The electron transport layer ETL can be prepared by a double-source co-evaporation method. The thickness of the electron transport layer ETL is 30 nm.

[0200] S14, evaporating an electron injection material on the side of the electron transport layer ETL away from the second hole blocking layer HBL2 to form an electron injection layer EIL. The material of the electron injection layer EIL can be ytterbium (Yb). The thickness of the electron injection layer EIL is 1 nm.

[0201] S15, forming a cathode 2 on the side of the electron injection layer EIL away from the electron transport layer ETL. The material of the cathode 2 includes Mg and Al doped together, and the mass ratio of the two is 8:2. The cathode 2 can be prepared by a double-source co-evaporation method. The thickness of the cathode 2 is 13 nm.

[0202] S16, evaporating a light extraction material on the side of the cathode 2 away from the anode 1 to form a light extraction layer CPL. The thickness of the light extraction layer CPL is 60 nm.

[0203] The substrate described above containing the light extraction layer CPL can be packaged by a glass UV packaging method. If the material TFE (tetrafluoroethylene resin) is packaged, lithium fluoride (LiF) or an organic material with a low refractive index (refractive index n less than or equal to 1.6) needs to be evaporated on the light extraction layer CPL.

[0204] In addition, the display device provided by the embodiments of the present disclosure includes the display substrate of any one of the above embodiments. The display device can be, for example, a mobile phone, a tablet computer, a television, a display, a notebook computer, a digital photo frame, a vehicle-mounted device, or any product with a display function. Other essential components of the display device are understood by those skilled in the art and are not described here to avoid repetition. They should not be considered as a limitation on the present disclosure.

[0205] It is understood that the above embodiments are only exemplary for illustrating the principles of the present disclosure, and the present disclosure is not limited thereto. Various modifications and improvements can be made by those of ordinary skill in the art without departing from the spirit and essence of the present disclosure, and these modifications and improvements are also considered to be within the scope of protection of the present disclosure.

Claims

1. A light emitting device, comprising: an anode; a cathode; a plurality of light emitting units disposed between the anode and the cathode; and a charge generation unit disposed between adjacent light emitting units; wherein at least one first light emitting unit and one second light emitting unit are included in the plurality of light emitting units, and the first light emitting unit is closer to the anode than the second light emitting unit; wherein the first light emitting unit comprises a first light emitting layer and a first hole transport sub-unit disposed on a side of the first light emitting layer close to the anode; wherein the second light emitting unit comprises a second light emitting layer and a second hole transport sub-unit disposed on a side of the second light emitting layer close to the anode; and wherein a thickness of the first hole transport sub-unit of the first light emitting unit is greater than a thickness of the second hole transport sub-unit of the second light emitting unit. The charge generation unit comprises an N-type doped charge generation layer and a P-type doped charge generation layer disposed in sequence in a direction away from the anode; a surface of the N-type doped charge generation layer in contact with the P-type doped charge generation layer is a first surface; a surface of the first light emitting layer close to the N-type doped charge generation layer is a second surface, and a distance from the first surface to the second surface is a first distance. The ratio of the thickness of the first hole transport sub-unit to the first distance is between 4 and 10. The first distance is between 15 nm and 30 nm. The first light emitting unit further comprises a first hole blocking layer disposed on a side of the first light emitting layer close to the cathode; and the thickness of the first hole blocking layer is between 5 nm and 10 nm.

2. The light-emitting device according to claim 1, wherein The first hole transport sub-unit comprises at least a first hole transport layer; and the second hole transport sub-unit comprises at least a second hole transport layer. Ar1-Ar3 are each independently selected from any one of hydrogen, deuterium, nitrile, nitro, hydroxyl, carbonyl, ester, imide, amide, alkyl, cycloalkyl, alkoxy, aryloxy, alkylthio, arylthio, alkylsulfonyl, arylsulfonyl, alkenyl, silyl, boryl, aminyl, arylphosphino, phosphinoyl, aryl, and heteroaryl; or any adjacent groups of Ar1-Ar3 combine to form a ring; and N represents a nitrogen atom.

3. The light emitting device of claim 2, wherein, The first hole transport sub-unit comprises at least a first hole transport layer; and the second hole transport sub-unit comprises at least a second hole transport layer.

4. The light-emitting device according to claim 3, wherein Ar4-Ar7 are each independently selected from any one of hydrogen, deuterium, nitrile, nitro, hydroxyl, carbonyl, ester, imide, amide, alkyl, cycloalkyl, alkoxy, aryloxy, alkylthio, arylthio, alkylsulfonyl, arylsulfonyl, alkenyl, silyl, boryl, aminyl, arylphosphino, phosphinoyl, aryl, and heteroaryl; or any adjacent groups of Ar4-Ar7 combine to form a ring; and L represents a substituted or unsubstituted arylene or heteroarylene.

5. The light emitting device of claim 1, wherein, * represents a position of the structural formula (I) or a position of the structural formula (II). The structural general formula (I) of the material of the first hole transport layer and the material of the second hole transport layer is as follows: * represents a position of the structural formula (I) or a position of the structural formula (II).

6. The light-emitting device according to claim 1, wherein ​ The structural general formula (II) of the material of the first hole transport layer and the material of the second hole transport layer is as follows: ​ 7. The light-emitting device according to claim 5, wherein Ar1to Ar3are selected from any one of the following structures: ​ 8. The light-emitting device according to claim 6, wherein Ar4to Ar7are selected from any one of the following structures: ​ 9. The light-emitting device according to claim 6, wherein L is selected from any one of the following structures:

10. The light-emitting device according to claim 1, wherein The first hole transport sub-unit comprises a first hole injection layer, a first hole transport layer, and a first electron blocking layer arranged in sequence away from the anode; The second hole transport sub-unit comprises a second hole transport layer and a second electron blocking layer arranged in sequence away from the anode. 11.A display panel comprising a plurality of light emitting devices of different colors, the plurality of light emitting devices of different colors comprising a red light emitting device, a green light emitting device, and a blue light emitting device; Each light emitting device comprises an anode, a cathode, a plurality of light emitting units arranged between the anode and the cathode, and a charge generation unit arranged between adjacent light emitting units; At least one first light emitting unit and one second light emitting unit are comprised in the plurality of light emitting units, and the first light emitting unit is closer to the anode than the second light emitting unit; The first light emitting unit comprises a first light emitting layer, and a first hole transport sub-unit arranged on a side of the first light emitting layer close to the anode; The second light emitting unit comprises a second light emitting layer, and a second hole transport sub-unit arranged on a side of the second light emitting layer close to the anode; and The thickness of the first hole transport sub-unit of the first light emitting unit is greater than the thickness of the second hole transport sub-unit of the second light emitting unit. 12.The display panel of claim 11, wherein The charge generation unit comprises an N-type doped charge generation layer and a P-type doped charge generation layer arranged in sequence away from the anode; a surface of the N-type doped charge generation layer in contact with the P-type doped charge generation layer is a first surface; a surface of the first light emitting layer close to the N-type doped charge generation layer is a second surface, and a distance from the first surface to the second surface is a first distance; For the red light emitting device, a ratio of the thickness of the first hole transport sub-unit to the first distance is between 6 and 10; for the green light emitting device, a ratio of the thickness of the first hole transport sub-unit to the first distance is between 5 and 8; and for the blue light emitting device, a ratio of the thickness of the first hole transport sub-unit to the first distance is between 4 and 6.

13. The display panel of claim 12, wherein, The thickness of the first hole transport sub-unit of the red light emitting device is greater than the thickness of the first hole transport sub-unit of the green light emitting device; and the thickness of the first hole transport sub-unit of the green light emitting device is greater than the thickness of the first hole transport sub-unit of the blue light emitting device.

14. The display panel of claim 13, wherein, For the red light emitting device, the thickness of the first hole transport sub-unit is between 170 nm and 230 nm; for the green light emitting device, the thickness of the first hole transport sub-unit is between 130 nm and 170 nm; and for the blue light emitting device, the thickness of the first hole transport sub-unit is between 90 nm and 130 nm.

15. The display panel of claim 13 or 14, wherein, The first distance is between 15 nm and 30 nm. 16.The display panel of claim 11, wherein The charge generation unit comprises an N-type doped charge generation layer and a P-type doped charge generation layer arranged in sequence in a direction away from the anode; a surface of the N-type doped charge generation layer in contact with the P-type doped charge generation layer is a first surface; a surface of the second light-emitting layer close to the N-type doped charge generation layer is a third surface, and a distance from the third surface to the first surface closest thereto is a second distance; a surface of the second light-emitting layer close to the cathode side is a fourth surface, and a shortest distance from the fourth surface to the cathode is a third distance; For the red light-emitting device, a ratio of the second distance to the third distance is between 2 and 3.2; for the green light-emitting device, a ratio of the second distance to the third distance is between 1.8 and 2.8; and for the blue light-emitting device, a ratio of the second distance to the third distance is between 1.6 and 2.

6.

17. The display panel of claim 16, wherein, For the red light-emitting device, the second distance is between 80 nm and 110 nm; for the green light-emitting device, the second distance is between 65 nm and 95 nm; and for the blue light-emitting device, the second distance is between 55 nm and 85 nm.

18. The display panel of claim 16, wherein, For the red light-emitting device, a thickness of the second hole transport sub-unit is between 70 nm and 90 nm; for the green light-emitting device, a thickness of the second hole transport sub-unit is between 60 nm and 80 nm; and for the blue light-emitting device, a thickness of the second hole transport sub-unit is between 50 nm and 70 nm.

19. The display panel of claim 11, wherein, The first hole transport sub-unit comprises a first hole injection layer, a first hole transport layer, and a first electron blocking layer arranged in sequence in a direction away from the anode; and The second hole transport sub-unit comprises a second hole transport layer and a second electron blocking layer arranged in sequence in a direction away from the anode.

20. The display panel of claim 19, wherein, The first hole injection layers of the plurality of light-emitting devices have the same thickness, and the first hole injection layers of the plurality of light-emitting devices have an integrated structure; and The first hole transport layers of the plurality of light-emitting devices have the same thickness, and the first hole transport layers of the plurality of light-emitting devices have an integrated structure.

21. The display panel of claim 19, wherein, A thickness of the first electron blocking layer of the red light-emitting device is greater than a thickness of the first electron blocking layer of the green light-emitting device; and A thickness of the first electron blocking layer of the green light-emitting device is greater than a thickness of the first electron blocking layer of the blue light-emitting device.

22. The display panel of claim 21, wherein, A thickness of the second electron blocking layer of the red light-emitting device is greater than a thickness of the second electron blocking layer of the green light-emitting device; and A thickness of the second electron blocking layer of the green light-emitting device is greater than a thickness of the second electron blocking layer of the blue light-emitting device.

23. The display panel of claim 11, wherein, Materials of the first electron blocking layers corresponding to the red light-emitting device, the green light-emitting device, and the blue light-emitting device are different; and materials of the second electron blocking layers corresponding to the red light-emitting device, the green light-emitting device, and the blue light-emitting device are different; and The material of the first light-emitting layer corresponding to each of the red light-emitting device, the green light-emitting device and the blue light-emitting device is different; the material of the second light-emitting layer corresponding to each of the red light-emitting device, the green light-emitting device and the blue light-emitting device is different.

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