An electroluminescent device, display apparatus

Abstract

This disclosure relates to the field of display technology, specifically to an electroluminescent device and a display apparatus. The electroluminescent device includes: a first electrode and a second electrode; a first light-emitting layer disposed between the first electrode and the second electrode, the first light-emitting layer comprising a first host material and a first dopant material, the first dopant material being uniformly doped in the first host material; and a second light-emitting layer disposed between the first light-emitting layer and the second electrode, comprising a second host material and a second dopant material, wherein the second light-emitting layer includes a first sub-layer and a second sub-layer disposed along the stacking direction of the first light-emitting layer and the second light-emitting layer, the first sub-layer being disposed between the second sub-layer and the first light-emitting layer, and the second dopant material being uniformly doped in the second host material of the first sub-layer but not in the second host material of the second sub-layer.

Description

Technical Field

[0001] This application relates to the field of display technology, and more specifically, to an electroluminescent device and a display apparatus. Background Technology

[0002] Organic light-emitting diodes (OLEDs) have broad application prospects in the display and lighting fields, with improving the efficiency of blue light-emitting devices being particularly crucial. Currently, blue OLEDs mainly rely on the triplet-triplet annihilation (TTA) mechanism to convert high-concentration triplet excitons into light-emitting singlet excitons, and then transfer energy to the light-emitting acceptor, thereby achieving blue light emission. The TTA process has a significant effect on improving device efficiency. Summary of the Invention

[0003] This application provides an electroluminescent device and a display apparatus, aiming to solve the problem of how to improve the luminous efficiency of blue OLEDs.

[0004] A first aspect of this application provides an electroluminescent device, the electroluminescent device comprising: First electrode and second electrode; A first light-emitting layer is disposed between the first electrode and the second electrode. The first light-emitting layer includes a first host material and a first doped material, wherein the first doped material is uniformly doped into the first host material. The second light-emitting layer, disposed between the first light-emitting layer and the second electrode, comprises a second host material and a second doped material, wherein... The second light-emitting layer includes a first sub-layer and a second sub-layer disposed along the stacking direction of the first light-emitting layer and the second light-emitting layer. The first sub-layer is disposed between the second sub-layer and the first light-emitting layer. The second doping material is uniformly doped in the second host material of the first sub-layer, but not in the second host material of the second sub-layer.

[0005] In one alternative implementation, the thickness of the first sub-layer is greater than the thickness of the first light-emitting layer.

[0006] In one optional embodiment, the second light-emitting layer further includes a third sub-layer disposed between the first sub-layer and the first light-emitting layer. The third sub-layer includes the second host material, and the second dopant material is not doped into the second host material of the third sub-layer.

[0007] In one alternative implementation, the thickness of the third sublayer is less than or equal to the thickness of the first sublayer.

[0008] In one alternative implementation, the distance between the surface of the first sublayer away from the first light-emitting layer and the surface of the first light-emitting layer near the first sublayer is less than or equal to 10 nm.

[0009] In one alternative implementation, the T1 energy level of the first light-emitting layer is greater than the T1 energy level of the second light-emitting layer.

[0010] In one optional embodiment, the electroluminescent device further includes an electron transport region and a hole transport region, wherein the hole transport region is disposed between the first electrode and the first light-emitting layer, and the electron transport region is disposed between the second electrode and the second light-emitting layer. The hole transport region includes at least one of the following: A hole injection layer is disposed between the first electrode and the first light-emitting layer; A hole transport layer is disposed between the hole injection layer and the first light-emitting layer; An electron blocking layer is disposed between the hole transport layer and the first light-emitting layer; The electron transmission region includes at least one of the following: An electron injection layer is disposed between the second electrode and the second light-emitting layer; An electron transport layer is disposed between the electron injection layer and the second light-emitting layer; A hole blocking layer is disposed between the electron transport layer and the second light-emitting layer.

[0011] In one alternative implementation, the thickness of the first sublayer is greater than or equal to 5 nm and less than or equal to 10 nm.

[0012] In one optional embodiment, both the first light-emitting layer and the second light-emitting layer are blue light-emitting layers.

[0013] A second aspect of this application provides a display device, the display device including an electroluminescent device as described in any one of the first aspects of this application.

[0014] Beneficial effects: This application provides an electroluminescent device and a display device. The electroluminescent device includes: a first electrode and a second electrode; a first light-emitting layer disposed between the first electrode and the second electrode, the first light-emitting layer including a first host material and a first dopant material, the first dopant material being uniformly doped in the first host material; and a second light-emitting layer disposed between the first light-emitting layer and the second electrode, including a second host material and a second dopant material, wherein the second light-emitting layer includes a first sub-layer and a second sub-layer disposed along the stacking direction of the first light-emitting layer and the second light-emitting layer, the first sub-layer being disposed between the second sub-layer and the first light-emitting layer, and the second dopant material being uniformly doped in the second host material of the first sub-layer but not in the second host material of the second sub-layer.

[0015] In this embodiment, the doped region of the second emitting layer is compressed within the first sublayer, keeping the second sublayer undoped. The narrowing of the doped region confines carrier recombination to a thinner spatial area, significantly reducing the exciton recombination region width, greatly increasing the local concentration of triplet excitons, and enhancing the TTA process, thereby effectively improving the efficiency of the blue light-emitting device. Simultaneously, the undoped second sublayer does not participate in exciton generation, locking the presence of triplet excitons within the doped region, preventing exciton diffusion and dissipation into wider regions, increasing the TTF contribution ratio, and suppressing non-radiative recombination. By narrowing the doped region, both the recombination region and exciton distribution are compressed, synergistically improving the device's luminous efficiency and stability.

[0016] The above description is merely an overview of the technical solution disclosed herein. In order to better understand the technical means of this disclosure and to implement it in accordance with the contents of the specification, and to make the above and other objects, features and advantages of this disclosure more apparent and understandable, specific embodiments of this disclosure are described below. Attached Figure Description

[0017] To more clearly illustrate the technical solutions of the embodiments of this application, the drawings used in the description of the embodiments of this application will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0018] Figure 1 This is a schematic diagram of the hierarchical structure of an electroluminescent device according to an embodiment of this application; Figure 2 This is a schematic diagram of the hierarchical structure of an electroluminescent device with a third sub-layer according to an embodiment of this application; Figure 3 This is a schematic diagram of energy transfer between a first light-emitting layer and a second light-emitting layer according to an embodiment of this application.

[0019] Explanation of reference numerals in the attached figures: 11, First electrode; 12, Second electrode; 13, Hole transport region; 131, Hole injection layer; 132, Hole transport layer; 133, Electron blocking layer; 141, First light-emitting layer; 142, Second light-emitting layer; 1421, First sublayer; 1422, Second sublayer; 1423, Third sublayer; 15, Electron transport region; 151, Electron injection layer; 152, Electron transport layer; 153, Hole blocking layer. Detailed Implementation

[0020] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0021] To make the objectives, technical solutions, and advantages of the embodiments of this disclosure clearer, the technical solutions of the embodiments of this disclosure will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this disclosure, and not all embodiments. Based on the embodiments of this disclosure, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this disclosure.

[0022] Organic light-emitting diodes (OLEDs), with their advantages of self-illumination, thinness, flexibility, and high contrast, have become the core development direction of next-generation display and lighting technologies. Among them, blue OLED devices, due to their indispensable role in full-color displays and their high photon energy, have always been a research hotspot and challenge in the field.

[0023] Currently, the mainstream light-emitting mechanism of blue OLED devices relies on the triplet-triplet annihilation (TTA) process. In this mechanism, a high concentration of triplet excitons within the emissive layer undergoes collisional annihilation to generate light-emitting singlet excitons, which then transfer energy to light-receiving acceptor molecules (such as blue fluorescent dopants), thereby achieving blue light emission. The TTA process can effectively utilize the energy of triplet excitons that would otherwise not decay radiatively, and is therefore considered an important way to improve the efficiency of blue OLED devices.

[0024] However, the formation rate of the TTA process is directly proportional to the local concentration of triplet excitons. In other words, the higher the concentration and the more concentrated the distribution of triplet excitons, the more significant the TTA effect and the more pronounced the improvement in device efficiency. This necessitates the formation of the narrowest possible exciton recombination region within the emitting layer (EML) to significantly increase the exciton density. Simultaneously, an tunable triplet-triplet fusion (TTF) recombination region is also beneficial for further efficiency optimization.

[0025] In theory, by precisely adjusting the energy level matching and carrier mobility of each functional layer, the exciton recombination region can be effectively confined to the vicinity of the interface between the Prime layer (i.e., the electron blocking layer) and the luminescent layer, thus meeting the requirement of a narrow recombination region. As an electron blocking layer, the interface between the Prime layer and the EML is the location where holes and electrons most easily meet and recombine. The design should aim to concentrate the recombination region as much as possible at this interface.

[0026] However, in actual device structures, due to the inherent carrier transport characteristics of the first light-emitting layer (EML1) (such as insufficient hole or electron mobility, energy level barrier mismatch, etc.), the carrier transport distribution within this layer is too dispersed, and the exciton recombination region is significantly broadened rather than concentrated in a narrow band. The broadening of the recombination region directly reduces the local concentration of triplet excitons, resulting in a significant reduction in the efficiency of the TTA process, thereby limiting the overall external quantum efficiency of blue OLED devices.

[0027] Therefore, how to effectively compress the width of the exciton recombination region and stably confine it near the interface of the electron blocking layer / emitting layer while maintaining the advantages of the TTA / TTF mechanism has become a key technical challenge for improving the efficiency of blue OLED devices.

[0028] In view of this, embodiments of this application provide an electroluminescent device. Figure 1 This illustration shows a schematic diagram of the hierarchical structure of an electroluminescent device according to an embodiment of this application, as follows: Figure 1As shown, the electroluminescent device includes a first electrode 11 and a second electrode 12. The first electrode 11 serves as the anode, used to inject holes into the device; the second electrode 12 serves as the cathode, used to inject electrons into the device. A first light-emitting layer 141 and a second light-emitting layer 142 are sequentially stacked between the first electrode 11 and the second electrode 12. The first light-emitting layer 141 is located closer to the anode and primarily functions to generate excitons initially and transfer energy. The second light-emitting layer 142 is located between the first light-emitting layer 141 and the second electrode 12, serving as the main light-emitting functional layer, used to receive energy from the first light-emitting layer 141 and achieve efficient light emission. Through this stacked structure, electrons and holes recombine within the light-emitting layers to form excitons, thereby converting electrical energy into light energy output.

[0029] In this embodiment, the first light-emitting layer 141 includes a first host material and a first dopant material uniformly doped therein. The first host material serves as a matrix, carrying dopants and transporting charge carriers, providing a host environment for exciton generation; the first dopant material serves as an auxiliary light-emitting component, receiving energy and participating in the exciton recombination process. The second light-emitting layer 142 includes a second host material and a second dopant material, wherein the second dopant material is not uniformly distributed throughout the entire second light-emitting layer 142, but is only uniformly doped in a portion of the second host material on the side of the second light-emitting layer 142 closest to the first light-emitting layer 141. By narrowing the doped region, the recombination space of charge carriers is confined to a thinner range, the width of the exciton recombination region is significantly reduced, resulting in a significant increase in the local concentration of triplet excitons in the limited space, and the triplet-triplet annihilation (TTA) process is enhanced accordingly, thereby effectively improving the luminous efficiency of the blue light device.

[0030] Specifically, the second light-emitting layer 142 is provided with a first sub-layer 1421 and a second sub-layer 1422 sequentially along the stacking direction of the first light-emitting layer 141 and the second light-emitting layer 142, wherein the first sub-layer 1421 is located between the second sub-layer 1422 and the first light-emitting layer 141. The second doping material is uniformly doped in the second host material of the first sub-layer 1421, while the second host material of the second sub-layer 1422 is not doped with the second doping material. Through the above arrangement, the doped region is precisely limited to the first sub-layer 1421 near the first light-emitting layer 141, and the undoped second sub-layer 1422 does not participate in carrier recombination, thereby locking the generation and existence range of triplet excitons within the doped region, avoiding exciton diffusion and dissipation to a wider region, maximizing the contribution ratio of triplet-triplet fusion (TTF), suppressing nonradiative recombination, and synergistically improving the luminous efficiency and stability of the device. Meanwhile, the undoped second sublayer 1422 does not participate in exciton generation, confining the existence of triplet excitons within the doped first sublayer 1421. This prevents excitons from diffusing and dissipating into a wider region, increasing the TTF contribution ratio and suppressing nonradiative recombination. By narrowing the doped region, both the recombination region and exciton distribution are compressed, synergistically improving the device's luminous efficiency and stability.

[0031] In some alternative embodiments, the thickness of the first sublayer 1421 is greater than the thickness of the first light-emitting layer 141. By setting this thickness relationship, it is ensured that the doped region has sufficient space thickness to accommodate carrier recombination, while keeping the first light-emitting layer 141 relatively thin, which is beneficial for the efficient transfer of excitons to the second light-emitting layer 142.

[0032] Optionally, the thickness of the first light-emitting layer 141 is greater than or equal to 3 nm and less than or equal to 5 nm. Since the effective operating distance of Dexter energy transfer is approximately 5 nm, setting the thickness of the first light-emitting layer 141 to 5 nm ensures that exciton energy is efficiently transferred to the adjacent second light-emitting layer 142 via the Dexter mechanism, avoiding a decrease in energy transfer efficiency due to excessive layer thickness. Simultaneously, the lower limit of 3 nm ensures that the first light-emitting layer 141 possesses sufficient structural integrity, preventing uneven film formation or device short circuits due to excessive thinness.

[0033] Optionally, the thickness of the first sublayer 1421 is greater than or equal to 5 nm and less than or equal to 10 nm. This thickness range provides sufficient space for carrier recombination, enabling triplet excitons to reach a high local concentration within the doping region, while avoiding excessive thickness that would cause the exciton recombination region to widen and the concentration to be diluted. This achieves an optimal balance between recombination space and exciton density, ensuring the efficient execution of the TTA process.

[0034] In some alternative embodiments, the thickness of the second light-emitting layer 142 is greater than or equal to 10 nm and less than or equal to 15 nm.

[0035] In some alternative implementations, such as Figure 1 As shown, the surface of the first sub-layer 1421 can directly contact the first light-emitting layer 141, meaning that only the first sub-layer 1421 is disposed between the second sub-layer 1422 and the first light-emitting layer 141. This direct-contact structure precisely limits the carrier recombination region to the vicinity of the interface between the first sub-layer 1421 and the first light-emitting layer 141, eliminating the need for an additional intermediate layer. This avoids the carrier injection barrier and energy loss caused by an increased interface, which helps reduce the device's operating voltage and improve efficiency. Simultaneously, the direct-contact interface minimizes the exciton energy transfer path, ensuring that excitons generated in the first light-emitting layer 141 can be efficiently transferred to the first sub-layer 1421 of the second light-emitting layer 142 to participate in light emission, further improving energy utilization.

[0036] In some alternative implementations, Figure 2 This illustration shows a schematic diagram of the hierarchical structure of an electroluminescent device with a third sublayer according to an embodiment of this application. Figure 2 As shown, the second luminescent layer 142 further includes a third sub-layer 1423, which is disposed between the first sub-layer 1421 and the first luminescent layer 141. The third sub-layer 1423 includes the second host material, and the second doped material is not doped into the second host material of the third sub-layer; that is, the third sub-layer 1423 is an undoped region. In this embodiment, the first sub-layer 1421 doped with the second doped material is sandwiched between the undoped second sub-layer 1422 and the third sub-layer 1423, forming a three-layer sandwich structure of undoped / doped / undoped. Through the above structural configuration, the second sub-layer 1422 and the third sub-layer 1423 on both sides of the first sub-layer 1421 together constitute a "double barrier". The two undoped regions strictly limit the existence range of triplet excitons within the middle doped layer, effectively suppressing the escape and diffusion dissipation of excitons to the non-luminescent regions on both sides, maximizing the contribution ratio of the TTF process. The sandwich layout formed by the three-layer structure achieves simultaneous optimization in two dimensions: compressing the width of the recombination region and restricting the spatial distribution of excitons, thus balancing efficiency improvement and stability enhancement.

[0037] In some optional embodiments, the thickness of the third sublayer 1423 is less than or equal to the thickness of the first sublayer 1421. This thickness setting ensures that the third sublayer 1423, located between the first sublayer 1421 and the first light-emitting layer 141, remains relatively thin. As an undoped buffer layer, the third sublayer 1423's thickness does not exceed that of the first sublayer 1421, allowing the doped region to occupy a dominant thickness proportion within the entire second light-emitting layer 142. This ensures that the main regions for carrier recombination and exciton generation remain concentrated within the doped first sublayer 1421, preventing the recombination region from shifting to the undoped region due to an excessively thick buffer layer. This maintains a high concentration of triplet exciton density, ensuring efficient TTA (Transient Amplification and Transformation) processes and balancing the dual requirements of interface optimization and luminescence efficiency.

[0038] In some alternative embodiments, regardless of whether a stacked structure is used in which the first sublayer 1421 is in direct contact with the first light-emitting layer 141, or a sandwich structure with a third sublayer 1423 disposed between the first sublayer 1421 and the first light-emitting layer 141, the distance between the surface of the first sublayer 1421 away from the first light-emitting layer 141 and the surface of the first light-emitting layer 141 close to the first sublayer 1421 should not be too large. This distance essentially limits the total thickness of the entire exciton recombination and energy transfer channel, and its magnitude directly determines the efficiency of exciton transfer from the first light-emitting layer 141 to the second light-emitting layer 142 and the degree to which the recombination region is confined.

[0039] Optionally, the distance between the surface of the first sublayer 1421 away from the first light-emitting layer 141 and the surface of the first light-emitting layer 141 closer to the first sublayer 1421 is less than or equal to 10 nm. Since the effective distance for Dexter energy transfer is only about 5 nm, and the effective distance for Förster energy transfer is typically within 10 nm, controlling this distance within 10 nm ensures that the exciton energy generated in the first light-emitting layer 141 is efficiently transferred to the second doped material in the first sublayer 1421 through the energy transfer mechanism, avoiding energy dissipation during the transfer process due to excessive distance. Simultaneously, this distance limitation also ensures that the entire carrier recombination region is confined within the limited space between the first light-emitting layer 141 and the first sublayer 1421, preventing the recombination region from expanding into the undoped region, maintaining a high local concentration of triplet excitons, thereby ensuring the efficient execution of the TTA process and optimizing device efficiency.

[0040] In some alternative implementations, the T1 energy level (triple-state energy level) of the first emitting layer is greater than the T1 energy level of the second emitting layer.

[0041] In some optional embodiments, the electroluminescent device is a blue electroluminescent device, wherein both the first light-emitting layer 141 and the second light-emitting layer 142 are blue light-emitting layers. Figure 3 This illustration shows a schematic diagram of energy transfer between a first light-emitting layer and a second light-emitting layer according to an embodiment of this application, as shown below. Figure 3 As shown, in the blue light-emitting device, the energy transfer process between the first light-emitting layer (EML1) 141 and the second light-emitting layer (EML2) 142 is as follows: Inside the first light-emitting layer 141, excitons on the S1 level (first singlet state level) of the first host material (BH) first transition to its own T1 level (first triplet state level) through intersystem crossing (ISC), transferring energy from the singlet state to the triplet state. Subsequently, the triplet excitons on the T1 level of the first host material BH transfer energy to the S1 level of the first doped material (BlueDopant, BD) through the Förster resonance energy transfer (FRET) mechanism, exciting the doped material to the singlet excited state, and then radiatively transitioning back to the S0 level (ground state), realizing the blue light emission of the first light-emitting layer 141.

[0042] Simultaneously, some triplet excitons at the T1 level of the first host material BH transfer energy to the T1 level of the adjacent second host material (Host, BH) of the second emitting layer 142 via the Dexter energy transfer (DET) mechanism. After receiving energy, the triplet excitons at the T1 level of the second host material BH of the second emitting layer 142 collide through a triplet-triplet annihilation (TTA) process, transitioning to their own S1 level, converting two triplet excitons into one high-energy singlet exciton. Finally, the singlet excitons at the S1 level of the second host material BH of the second emitting layer 142 transfer energy to the S1 level of the second doped material (Blue Dopant, BD) via the Förster resonance energy transfer (FRET) mechanism, and then radiatively transition back to the S0 level, realizing the blue light emission of the second emitting layer 142. Through the cascaded design of the above energy transfer paths, the triplet excitons generated in the first light-emitting layer 141 can transfer energy to the second light-emitting layer 142 and release energy to the doped material through the synergistic effect of two mechanisms: Dexter energy transfer and Förster resonance energy transfer. This achieves full capture and efficient utilization of triplet excitons, significantly improving the luminous efficiency of the blue electroluminescent device.

[0043] In some optional embodiments, the electroluminescent device can be a top-emitting device or a bottom-emitting device. Taking a top-emitting device as an example, such as... Figure 1 As shown, the electroluminescent device further includes an electron transport region 15 and a hole transport region 13. The hole transport region 13 is disposed between the first electrode 11 and the first light-emitting layer 141, and the electron transport region 15 is disposed between the second electrode 12 and the second light-emitting layer 142. The hole transport region 13 is used to efficiently transport holes injected by the first electrode 11 to the light-emitting layer, and includes at least one of the following: a hole injection layer (HIL) 131, a hole transport layer (HTL) 132, and an electron block layer (EBL) 133. Specifically, the hole injection layer 131 is disposed between the first electrode 11 and the hole transport layer 132 to reduce the potential barrier for hole injection from the first electrode 11 and improve hole injection efficiency. The hole transport layer 132 is disposed between the hole injection layer 131 and the electron blocking layer 133 to provide a fast transport channel for holes and reduce the operating voltage of the device. The electron blocking layer 133 is disposed between the hole transport layer 132 and the first light-emitting layer 141 to prevent electrons injected from the second electrode 12 from crossing the first light-emitting layer 141 and entering the hole transport region 13, thus avoiding energy loss caused by electron recombination with holes in the non-light-emitting region. Furthermore, in this embodiment, by narrowing the doped region of the second light-emitting layer 142, the carrier recombination region is confined to the vicinity of the interface between the electron blocking layer 133 and the first light-emitting layer 141, providing a structural basis for achieving a narrow exciton recombination region.

[0044] The electron transport region 15 is used to efficiently transport electrons injected from the second electrode 12 to the light-emitting layer, and includes at least one of the following: an electron injection layer (EIL) 151, an electron transport layer (ETL) 152, and a hole block layer (HBL) 153. Specifically, the electron injection layer 151 is disposed between the second electrode 12 and the electron transport layer 152 to reduce the potential barrier for electron injection from the second electrode 12 and improve electron injection efficiency; the electron transport layer 152 is disposed between the electron injection layer 151 and the hole block layer 153 to provide an efficient transport path for electrons; the hole block layer 153 is disposed between the electron transport layer 152 and the second light-emitting layer 142 to prevent holes injected from the first electrode 11 from crossing the second light-emitting layer 142 and entering the electron transport region 15, avoiding recombination of holes with electrons in the non-light-emitting region, and confining the carrier recombination region within the second light-emitting layer 142 to further improve exciton utilization.

[0045] This application provides an electroluminescent device, comprising: a first electrode and a second electrode; a first light-emitting layer disposed between the first electrode and the second electrode, the first light-emitting layer comprising a first host material and a first dopant material, the first dopant material being uniformly doped in the first host material; and a second light-emitting layer disposed between the first light-emitting layer and the second electrode, comprising a second host material and a second dopant material, wherein the second light-emitting layer comprises a first sub-layer and a second sub-layer disposed along the stacking direction of the first light-emitting layer and the second light-emitting layer, the first sub-layer being disposed between the second sub-layer and the first light-emitting layer, and the second dopant material being uniformly doped in the second host material of the first sub-layer but not in the second host material of the second sub-layer.

[0046] In this embodiment, the doped region of the second emitting layer is compressed within the first sublayer, keeping the second sublayer undoped. The narrowing of the doped region confines carrier recombination to a thinner spatial area, significantly reducing the exciton recombination region width, greatly increasing the local concentration of triplet excitons, and enhancing the TTA process, thereby effectively improving the efficiency of the blue light-emitting device. Simultaneously, the undoped second sublayer does not participate in exciton generation, locking the presence of triplet excitons within the doped region, preventing exciton diffusion and dissipation into wider regions, increasing the TTF contribution ratio, and suppressing non-radiative recombination. By narrowing the doped region, both the recombination region and exciton distribution are compressed, synergistically improving the device's luminous efficiency and stability.

[0047] Based on the same inventive concept, this disclosure provides a display device, which includes the electroluminescent device described in this disclosure.

[0048] In one optional implementation, the display device may include a plurality of electroluminescent devices. For example, the display device may include a red electroluminescent device, a blue electroluminescent device, and a green electroluminescent device, wherein the blue electroluminescent device is the electroluminescent device mentioned in the embodiments of this application.

[0049] In some optional embodiments, the display device is a product with image display capabilities. Optionally, the display device can be used to display static images, such as pictures and photographs; the display device can also be used to display dynamic images, such as videos and game screens.

[0050] In some alternative implementations, the display device includes, but is not limited to, laptops, mobile phones, wireless devices, personal data assistants (PDAs), handheld or portable computers, GPS receivers / navigators, cameras, MP4 video players, camcorders, game consoles, watches, clocks, calculators, television monitors, flat panel displays, computer monitors, car displays, navigators, cockpit controllers and / or displays, displays of camera views, electronic photographs, electronic billboards or signs, projectors, packaging and aesthetic structures, etc.

[0051] The various embodiments in this specification are described in a progressive manner, with each embodiment focusing on the differences from other embodiments. The same or similar parts between the various embodiments can be referred to each other.

[0052] In the description of this specification, it should be understood that the terms "center," "thickness," "upper," "lower," "front," "rear," "horizontal," "top," "bottom," "inner," "outer," "axial," "radial," and "circumferential," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings, and are only for the convenience of describing this disclosure and simplifying the description, and are not intended to indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of this disclosure.

[0053] In this disclosure, unless otherwise expressly specified and limited, the terms "installation," "connection," "linking," "fixing," etc., should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part; they can refer to a mechanical connection, an electrical connection, or a communication connection; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication of two components or the interaction between two components. Those skilled in the art can understand the specific meaning of the above terms in this disclosure according to the specific circumstances.

[0054] In this disclosure, unless otherwise expressly specified and limited, "above" or "below" the second feature can include direct contact between the first and second features, or contact between the first and second features through another feature between them. Furthermore, "above," "over," and "on top" of the second feature includes the first feature being directly above or diagonally above the second feature, or simply indicates that the first feature is at a higher horizontal level than the second feature. "Below," "below," and "under" the second feature includes the first feature being directly above or diagonally above the second feature, or simply indicates that the first feature is at a lower horizontal level than the second feature.

[0055] The foregoing application provides many different implementations or examples for carrying out different structures of this disclosure. To simplify this disclosure, the components and arrangements of specific examples are described above. Of course, these are merely examples and are not intended to limit this disclosure. Furthermore, reference numerals and / or reference letters may be repeated in different examples; such repetition is for simplification and clarity and does not in itself indicate a relationship between the various implementations and / or arrangements discussed.

[0056] The terms "an embodiment," "embodiment," or "one or more embodiments" as used herein mean that a particular feature, structure, or characteristic described in connection with an embodiment is included in at least one embodiment of this disclosure. Furthermore, please note that the examples of the phrase "in one embodiment" do not necessarily all refer to the same embodiment.

[0057] Numerous specific details are set forth in the specification provided herein. However, it will be understood that embodiments of this disclosure may be practiced without these specific details. In some instances, well-known methods, structures, and techniques have not been shown in detail so as not to obscure the understanding of this specification.

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

[0059] The electroluminescent device and display apparatus provided in this disclosure have been described in detail above. Specific examples have been used to illustrate the principles and implementation methods of this disclosure. The description of the above embodiments is only for the purpose of helping to understand the method and core ideas of this disclosure. At the same time, for those skilled in the art, there will be changes in the specific implementation methods and application scope based on the ideas of this disclosure. Therefore, the content of this specification should not be construed as a limitation of this disclosure.

Claims

1. An electroluminescent device, characterized by The electroluminescent device includes: First electrode and second electrode; A first light-emitting layer is disposed between the first electrode and the second electrode. The first light-emitting layer includes a first host material and a first doped material, wherein the first doped material is uniformly doped into the first host material. The second light-emitting layer, disposed between the first light-emitting layer and the second electrode, comprises a second host material and a second doped material, wherein... The second light-emitting layer includes a first sub-layer and a second sub-layer disposed along the stacking direction of the first light-emitting layer and the second light-emitting layer. The first sub-layer is disposed between the second sub-layer and the first light-emitting layer. The second doping material is uniformly doped in the second host material of the first sub-layer, but not in the second host material of the second sub-layer.

2. The electroluminescent device according to claim 1, characterized in that The thickness of the first sub-layer is greater than the thickness of the first light-emitting layer.

3. The electroluminescent device according to claim 2, characterized in that, The second light-emitting layer further includes a third sub-layer disposed between the first sub-layer and the first light-emitting layer. The third sub-layer includes the second host material, and the second dopant material is not doped into the second host material of the third sub-layer.

4. The electroluminescent device according to claim 3, characterized in that, The thickness of the third sublayer is less than or equal to the thickness of the first sublayer.

5. The electroluminescent device according to any one of claims 1-4, characterized in that, The distance between the surface of the first sublayer away from the first light-emitting layer and the surface of the first light-emitting layer near the first sublayer is less than or equal to 10 nm.

6. The electroluminescent device according to claim 1, characterized in that, The T1 energy level of the first light-emitting layer is greater than the T1 energy level of the second light-emitting layer.

7. The electroluminescent device according to claim 1, characterized in that, The electroluminescent device further includes an electron transport region and a hole transport region, wherein the hole transport region is disposed between the first electrode and the first light-emitting layer, and the electron transport region is disposed between the second electrode and the second light-emitting layer; The hole transport region includes at least one of the following: A hole injection layer is disposed between the first electrode and the first light-emitting layer; A hole transport layer is disposed between the hole injection layer and the first light-emitting layer; An electron blocking layer is disposed between the hole transport layer and the first light-emitting layer; The electron transmission region includes at least one of the following: An electron injection layer is disposed between the second electrode and the second light-emitting layer; An electron transport layer is disposed between the electron injection layer and the second light-emitting layer; A hole blocking layer is disposed between the electron transport layer and the second light-emitting layer.

8. The electroluminescent device according to claim 1, characterized in that, The thickness of the first sublayer is greater than or equal to 5 nm and less than or equal to 10 nm.

9. The electroluminescent device according to claim 1, characterized in that, Both the first luminescent layer and the second luminescent layer are blue luminescent layers.

10. A display device, characterized in that, The display device includes an electroluminescent device as described in any one of claims 1-9.

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