Light-emitting device and display panel

Abstract

This application relates to the field of display technology, and particularly to a light-emitting device, display panel, and display apparatus, comprising a first electrode and a second electrode, the first electrode and the second electrode being disposed opposite to each other and spaced apart; a first light-emitting layer and a second light-emitting layer, the first light-emitting layer and the second light-emitting layer being disposed between the first electrode layer and the second electrode layer and in contact with each other; wherein, the first guest material is a phosphorescent dye, and the second guest material is a fluorescent dye; the LUMO energy level of the first host material is greater than the LUMO energy level of the second host material. This can improve the lifespan of the light-emitting device.

Description

Technical Field

[0001] This application relates to the field of display technology, and in particular to a light-emitting device and a display panel. Background Technology

[0002] Organic light-emitting diodes (OLEDs) utilize a self-emissive light-emitting mechanism, eliminating the need for a backlight. When applied to display panels and devices, OLEDs result in thinner overall designs, facilitating lightweight and slim designs. Furthermore, OLEDs offer advantages such as high brightness, wide viewing angles, and fast response times.

[0003] However, organic light-emitting diodes (OLEDs) have a short lifespan. Summary of the Invention

[0004] This application provides a light-emitting device and a display panel, which aims to improve the lifespan of organic light-emitting diodes in the display panel.

[0005] In a first aspect, embodiments of this application provide a light-emitting device, including:

[0006] A first electrode and a second electrode, wherein the first electrode and the second electrode are disposed opposite to each other and spaced apart from each other; A first light-emitting layer and a second light-emitting layer are disposed between the first electrode layer and the second electrode layer and are in contact with each other; the first light-emitting layer includes a first host material and a first guest material; the second light-emitting layer includes a second host material and a second guest material; the first guest material is a phosphorescent dye and the second guest material is a fluorescent dye; An electron blocking layer is located between the first electrode and the first light-emitting layer; The HOMO energy level of the electron blocking layer is greater than that of the first host material.

[0007] In one possible implementation, The difference between the HOMO energy level of the electron blocking layer of the first host material and the HOMO energy level of the first host material is greater than or equal to 0.3 eV and less than or equal to 0.4 eV.

[0008] In one possible implementation, The LUMO energy level of the first host material is greater than that of the second host material.

[0009] In one possible implementation, The difference between the LUMO energy level of the first host material and the LUMO energy level of the second host material is greater than or equal to 0.2 eV and less than or equal to 0.4 eV.

[0010] In one possible implementation, The triplet energy level of the electron blocking layer is greater than the triplet energy level of the first host material; And / or, the triplet energy level of the phosphorescent dye is lower than the triplet energy level of the first host material; And / or, the triplet energy level of the second host material is lower than the triplet energy level of the first host material.

[0011] In one possible implementation, the ratio of the electron mobility of the first host material to the electron mobility of the second host material is less than 1; In one possible implementation, The ratio of the hole mobility of the first main material to the hole mobility of the second main material is greater than 1.

[0012] In one possible implementation, The normalized intensity value at the intersection of the absorption spectrum of the fluorescent dye and the emission spectrum of the phosphorescent dye is greater than or equal to 0.8 and less than or equal to 1. In one possible implementation, The normalized intensity value at the intersection of the emission spectrum of the fluorescent dye and the emission spectrum of the phosphorescent dye is greater than or equal to 0.6 and less than or equal to 0.9. In one possible implementation, The normalized intensity value at the shoulder peak of the emission spectrum of the phosphorescent dye is less than 0.5.

[0013] In one possible implementation, The thickness of the first light-emitting layer ranges from 50 Å to 100 Å, and the thickness of the second light-emitting layer ranges from 150 Å to 200 Å. In one possible implementation, The doping concentration of the phosphorescent dye in the first luminescent layer ranges from 8% to 12%. In one possible implementation, The doping concentration of the fluorescent dye in the second luminescent layer ranges from 1% to 3%.

[0014] Secondly, this application provides a display panel, the display panel including the light-emitting device described in the first aspect above.

[0015] This application embodiment, by setting a second emitting layer including a second guest material that is fluorescent, and designing the electron blocking layer to have a HOMO energy level higher than that of the first host material, ensures that holes and electrons recombine at the interface between the first and second emitting layers. This significantly reduces the carrier density and triplet exciton concentration within the first emitting layer, thereby effectively suppressing the molecular bond breaking problem caused by high-energy excitons within the first emitting layer and greatly improving the lifespan of the light-emitting device. Attached Figure Description

[0016] To more clearly illustrate the technical solutions of the embodiments of this application, the drawings used in 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.

[0017] Figure 1A A schematic diagram of energy transfer in the phosphorescence process in existing technologies. Figure 1B A schematic diagram of energy transfer in the fluorescence emission process in the prior art. Figure 2 This is a schematic diagram of the structure of a light-emitting device provided in an embodiment of this application; Figure 3 This is a schematic diagram of another light-emitting device provided in an embodiment of this application; Figure 4 This is a schematic diagram of the energy transfer path of a light-emitting device provided in an embodiment of this application; Figure 5 This is a schematic diagram of the absorption spectrum of a fluorescent dye, the emission spectrum of a phosphorescent dye, and the emission spectrum of a fluorescent dye provided in the embodiments of this application.

[0018] Explanation of reference numerals in the attached drawings: first electrode 10, first light-emitting layer 21, second light-emitting layer 22, hole injection layer 40, hole transport layer 50, electron blocking layer 60, hole blocking layer 70, electron transport layer 80, and electron injection layer 90. Detailed Implementation

[0019] The features and exemplary embodiments of various aspects of this application will now be described in detail. To make the objectives, technical solutions, and advantages of this application clearer, the application will be further described in detail below with reference to the accompanying drawings and specific embodiments. It should be understood that the specific embodiments described herein are only configured to explain this application and are not configured to limit this application. For those skilled in the art, this application can be implemented without some of these specific details. The following description of the embodiments is merely to provide a better understanding of this application by illustrating examples of this application.

[0020] It should be noted that, in this document, relational terms such as "first" and "second" are used merely to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitations, an element defined by the phrase "comprising..." does not exclude the presence of additional identical elements in the process, method, article, or apparatus that includes the element.

[0021] It should be understood that when describing the structure of a component, when referring to a layer or region as being "above" or "on top of" another layer or region, it can mean that it is directly above the other layer or region, or that it contains other layers or regions between it and the other layer or region. Furthermore, if the component is flipped over, that layer or region will be located "below" or "under" the other layer or region.

[0022] In related technologies, when a certain voltage is applied to an organic light-emitting diode (OLED), electrons from the cathode and holes from the anode are injected into the HOMO and LUMO energy levels of the emitting layer, respectively. The injected electrons and holes are transported under the influence of an electric field. Electrons and holes recombine in the emitting layer through Coulomb interactions, generating excitons. Excitons can be classified into singlet excitons and triplet excitons based on their spin direction. Excitons release photons and emit light as they return from the excited state to the ground state. The light emitted from a singlet excited state transitioning back to the ground state is fluorescence; luminescent materials utilizing this mechanism are called fluorescent guest materials. The light emitted from a triplet excited state transitioning back to the ground state is phosphorescence; luminescent materials utilizing this mechanism are called phosphorescent guest materials.

[0023] Such as 1A and Figure 1B As shown, Figure 1A This is a schematic diagram of energy transfer during the phosphorescence process. Figure 1B This is a schematic diagram of energy transfer during the fluorescence emission process.

[0024] like Figure 1A and Figure 1BAs shown, electrons in organic light-emitting materials can transition from the ground state to an excited state under the influence of an applied voltage. S0 is the electronic ground state, the state in which the electron is not excited by energy, and its energy level is S0. S1 and T1 are excited states, the states after the electron is excited. Specifically, S1 is an excited singlet state, with the energy level S1, while T1 is an excited triplet state, also known as an excited triplet state, with the energy level T1.

[0025] Electrons in the excited singlet state S1 may undergo intersystem crossing (ISC) to enter the excited triplet state T1, which has a different spin state and a higher vibrational energy level. Electrons in the excited triplet state T1 first decrease to the lowest vibrational energy level through vibrational relaxation, and then return to the ground state S0 by emitting photons, thus producing phosphorescence.

[0026] An electron in the excited singlet state S1 first decreases to the lowest vibrational energy level of the excited state through vibrational relaxation, and then returns to the ground state S0 by emitting a photon, which results in fluorescence.

[0027] Clearly, when a voltage is applied to a luminescent material, the ground-state electrons are excited to higher excited-state energy levels, forming electron-hole pairs, i.e., generating excitons. Excitons can recombine from the excited state back to the ground state in the form of radiative recombination emitting light. For example, radiative recombination can produce fluorescence, corresponding to fluorescence displays, and radiative recombination can produce phosphorescence, corresponding to phosphorescent displays.

[0028] The inventors discovered that among OLED light-emitting devices, blue-emitting devices have a shorter lifespan compared to red- and green-emitting devices. Blue phosphorescence has attracted widespread attention due to its high efficiency, but the high triplet energy level of blue phosphorescent dyes leads to high exciton energies, causing molecular bond breakage and thus reducing device lifespan. Therefore, mass production of blue phosphorescent devices is difficult, making it crucial to improve their lifespan.

[0029] To address the aforementioned technical problems, embodiments of this application provide a light-emitting device, such as... Figure 2 As shown, the light-emitting device includes a first electrode 10, a first light-emitting layer 21, a second light-emitting layer 22, and an electron blocking layer 60.

[0030] The first electrode 10 and the second electrode 30 are disposed opposite to each other and spaced apart; the first light-emitting layer 21 and the second light-emitting layer 22 are disposed between the first electrode layer 10 and the second electrode layer 30 and are in contact with each other; the first light-emitting layer includes a first host material and a first guest material; the second light-emitting layer includes a second host material and a second guest material; the first guest material is a phosphorescent dye and the second guest material is a fluorescent dye; the electron blocking layer 60 is located between the first electrode 10 and the first light-emitting layer 21.

[0031] The HOMO energy level of the electron blocking layer is greater than that of the first host material.

[0032] In this embodiment, the first electrode 10 is the anode, the second electrode 30 is the cathode, and the first light-emitting layer 21 and the second light-emitting layer 22 can emit light under the action of the first electrode 10 and the second electrode 30, for example, emitting blue light. The first light-emitting layer 21 adopts a phosphorescent light-emitting system and includes a first host material and a first guest material, wherein the first guest material of the first light-emitting layer 21 is a phosphorescent material. The second light-emitting layer 22 adopts a fluorescent light-emitting system and includes a second host material and a second guest material, wherein the second guest material of the second light-emitting layer 22 is a fluorescent material.

[0033] In this embodiment of the application, the highest occupied molecular orbital (HOMO) refers to the orbital with the highest energy that is occupied by an electron in the molecular ground state.

[0034] In this application embodiment, the HOMO energy level of the electron blocking layer is greater than the HOMO energy level of the first host material.

[0035] It is understandable that, such as Figure 3 As shown, the light-emitting device further includes a hole injection layer 40, a hole transport layer 50, an electron blocking layer 60, a hole blocking layer 70, an electron transport layer 80, and an electron injection layer 90, which are sequentially stacked between the first electrode 10 and the second electrode 30; the first light-emitting layer 21 and the second light-emitting layer 22 are disposed between the electron blocking layer 60 and the hole blocking layer 70.

[0036] In a preferred implementation, the difference between the HOMO energy level of the electron blocking layer 60 and the HOMO energy level of the first host material is greater than or equal to 0.3 eV and less than or equal to 0.4 eV; for example, it can be 0.3 eV, 0.31 eV, 0.35 eV, 0.38 eV, 0.39 eV or 0.4 eV.

[0037] In this embodiment, after holes are injected from the anode, they sequentially pass through the hole injection layer 40 and the hole transport layer 50 to reach the interface between the electron blocking layer 60 and the first light-emitting layer 21. To ensure that sufficient holes can reach the first light-emitting layer 21 and accumulate at the interface, the HOMO energy level of the electron blocking layer 60 needs to be set to be greater than the HOMO energy level between the first host materials, so that a step-like decrease in HOMO energy level is formed from the hole transport layer 50 to the electron blocking layer 60 and then to the first light-emitting layer 21.

[0038] The electron blocking layer 60 can block electrons that diffuse backward or cross from the second light-emitting layer 22, preventing electrons from directly reaching the hole transport layer 50 or the anode without recombination, thus causing leakage current. The electron blocking layer 60 can also promote efficient hole injection by setting the HOMO energy level appropriately.

[0039] The HOMO energy level difference between a conventional electron blocking layer and the HOMO energy level of the first host material is typically between 0 and 0.3 eV. However, in the embodiments of this application, the HOMO energy level difference between the electron blocking layer and the first host material exceeds 0.3 eV. The HOMO energy level of the electron blocking layer is more than 0.3 eV lower than the HOMO energy level of the first host material, forming a "downhill" hole transport path from the electron blocking layer to the first emissive layer. Holes do not need to overcome a reverse potential barrier at this interface, thus allowing for efficient injection into the first emissive layer with almost no energy consumption.

[0040] Sufficient and efficient hole injection ensures that the hole density near the interface in the first light-emitting layer reaches a level matching the electron density. Since the HOMO energy level of the second host material is typically much deeper than that of the first host material, holes cannot cross this interface to enter the second light-emitting layer. Therefore, a large number of holes accumulate in the region near the interface of the first light-emitting layer. When a large number of holes accumulate here and encounter electrons that have also accumulated at the interface of the second light-emitting layer, the recombination probability increases dramatically. Therefore, the HOMO energy level design of the electron blocking layer ensures that holes and electrons recombine at the interface between the first and second light-emitting layers 21 and 22. This significantly reduces the carrier density and triplet exciton concentration inside the first light-emitting layer, effectively suppressing the molecular bond breaking problem caused by high-energy excitons inside the first light-emitting layer and greatly improving the lifespan of the light-emitting device.

[0041] This embodiment introduces an electron blocking layer and limits its HOMO energy level to be greater than that of the first host material, thereby constructing a hole injection energy level ladder and increasing the hole current density; forming a hole accumulation pool at the interface, which is precisely matched with the electron accumulation pool; reducing the driving voltage and reducing Joule heating; further reducing the hole (polaron) concentration in the bulk phase of the first light-emitting layer, ensuring the dominant position of interface recombination, thereby enhancing the lifetime extension effect of the present invention.

[0042] In another embodiment of this application, the LUMO energy level of the first host material is greater than the LUMO energy level of the second host material. The lowest occupied molecular orbital (LUMO) energy level refers to the energy level of the orbital with the lowest energy that is not occupied by electrons in the molecular orbital, which is the orbital into which electrons are most likely to jump.

[0043] When electrons are injected from the second electrode 30 into the second light-emitting layer 22, and holes are injected from the first electrode 10 into the first light-emitting layer 21, it is understood that the LUMO energy level of the first host material is higher than that of the second host material. This invention constructs an electron "barrier." Specifically, after electrons are injected from the cathode, they enter the second light-emitting layer 22. Due to the lower LUMO energy level of the second host material, electrons tend to transport and accumulate in the second light-emitting layer 22. When electrons attempt to further enter the first light-emitting layer 21, the higher LUMO energy level of the first host material forms an upward energy level step (electron barrier), effectively blocking and confining the electrons to the side of the second light-emitting layer 22 near the interface. Simultaneously, holes are injected from the anode into the first light-emitting layer. Because the first host material typically has a higher HOMO energy level, holes can be smoothly injected and transported in the first light-emitting layer, ultimately accumulating at the interface between the first and second light-emitting layers. That is, holes are blocked within the higher-energy-level first light-emitting layer and find it difficult to cross over to the lower-energy-level second host material. The synergistic effect of this energy level configuration allows holes and electrons to meet and recombine at the interface, generating excitons. Because the recombination region is precisely confined to the vicinity of the interface, the carrier density and triplet exciton concentration inside the first emitting layer are significantly reduced, thereby effectively suppressing the molecular bond breaking problem caused by high-energy excitons inside the first emitting layer and greatly improving the lifetime of the phosphorescent doped first emitting layer.

[0044] Furthermore, by setting a second light-emitting layer, this application changes the region where holes and electrons recombine to generate excitons, thereby improving the lifetime of the first light-emitting layer while also maintaining the advantage of the first light-emitting layer's high-efficiency blue phosphorescence emission.

[0045] In a preferred implementation, the difference between the LUMO energy levels of the first host material and the second host material is greater than or equal to 0.2 eV and less than or equal to 0.4 eV. For example, it can be set to 0.2 eV, 0.25 eV, 0.3 eV, 0.35 eV, or 0.4 eV.

[0046] By setting the energy difference between the LUMO levels of the first and second host materials to be greater than or equal to 0.2 eV and less than or equal to 0.4 eV, electrons are unlikely to leak into the first emitting layer. This means that the possibility of electron-hole recombination within the first emitting layer is extremely low, and the generation of triplet excitons is confined to the interface. Even if triplet excitons generated at the interface diffuse into the first emitting layer, their concentration decreases with increasing diffusion distance. Therefore, the triplet exciton concentration distribution in the first emitting layer exhibits a characteristic of being highest at the interface and decreasing sharply towards the interior. This effectively curbs exciton-related aging reactions within the first emitting layer at their source. Therefore, a relatively large energy level difference of 0.2 eV is required to prevent electrons from crossing the interface and participating in recombination within the first emitting layer, thereby reducing the triplet exciton concentration inside the first emitting layer and achieving optimal lifetime extension.

[0047] In another embodiment of this application, the triplet energy level of the electron blocking layer is greater than the triplet energy level T1 of the first host material; and / or, the triplet energy level T1 of the phosphorescent dye is less than the triplet energy level T1 of the first host material; and / or, the triplet energy level T1 of the second host material is less than the triplet energy level T1 of the first host material.

[0048] like Figure 4 As shown, Figure 4 This is a schematic diagram of the energy transfer path of a light-emitting device provided in an embodiment of this application. The triplet energy level T1 of the first host material is greater than the triplet energy level T1 of the phosphorescent dye (first guest material), and the triplet energy level T1 of the first host material is also greater than the triplet energy level T1 of the second host material. Figure 4 The triplet energy level of the electron blocking layer is not shown, but the triplet energy level of the electron blocking layer is greater than that of the triplet energy level of the first host material.

[0049] Triplet excitons have a long diffusion length in organic semiconductors, and if left unrestricted, they easily migrate to non-radiative functional layers (such as hole transport layers and electron transport layers), resulting in energy loss. In this embodiment, by setting the triplet energy level of the electron blocking layer to be higher than that of the first host material, it is ensured that triplet excitons generated or present in the first emitting layer cannot reverse-transfer to the electron blocking layer via Dexter energy transfer (DET). This is because Dexter transfer requires the triplet energy level of the donor to be higher than that of the acceptor, thus preventing triplet excitons from transitioning to the electron blocking layer.

[0050] Furthermore, this embodiment of the application sets the triplet energy level of the second host material to be lower than that of the first host material, thus constructing a triplet energy gradient. Specifically, the first host material has a higher triplet energy level, while the second host material has a lower triplet energy level. According to the hopping transport theory of triplet excitons in disordered organic semiconductors, excitons tend to migrate to sites with lower energies. Therefore, triplet excitons generated near the interface between the first and second light-emitting layers, or those diffused to this interface, will spontaneously undergo Dexter transfer from the first host material to the second host material. In other words, triplet excitons are actively "extracted" from the first light-emitting layer and transported to the second host material, thereby further reducing the residence time and concentration of triplet excitons in the first light-emitting layer and improving the lifetime of the light-emitting device.

[0051] This application embodiment further establishes that the triplet energy level of the phosphorescent dye is lower than that of the triplet energy level of the first host material, which is a fundamental condition for efficient phosphorescence sensitization. In the phosphorescent host-guest system, triplet excitons from the host material are transferred to the guest phosphorescent dye via Dexter, requiring the host's energy level to be higher than the guest's; otherwise, reverse energy transfer will occur, leading to phosphorescence quenching. This application embodiment ensures that triplet excitons injected into the host of the first emitting layer can be rapidly captured onto the phosphorescent dye molecules, thereby utilizing the high quantum yield and long excited-state lifetime of the phosphorescent dye to provide a stable donor excited state for subsequent Forster transfer (FET).

[0052] In another embodiment of this application, the ratio of the electron mobility of the first host material to the electron mobility of the second host material is less than 1; the ratio of the hole mobility of the first host material to the hole mobility of the second host material is greater than 1.

[0053] In this embodiment, compared to the second light-emitting layer, the first host material has the characteristics of high hole mobility and low electron mobility; compared to the first light-emitting layer, the second host material has the characteristics of low hole mobility and high electron mobility. Holes have high mobility in the first emissive layer, enabling them to rapidly travel to the interface between the first and second emissive layers. Upon arrival, due to the extremely low hole mobility in the second emissive layer, holes accumulate at the interface. Electrons, on the other hand, have high mobility in the second emissive layer, also enabling them to rapidly travel to the interface between the first and second emissive layers. Upon arrival, due to the low electron mobility in the first emissive layer, electrons accumulate at the interface. This recombination of electrons and holes at the interface between the first and second emissive layers to generate excitons, rather than within the first emissive layer itself, significantly reduces the triplet exciton concentration within the first emissive layer, preventing the breaking of chemical bonds in the material and improving the lifespan of the display device.

[0054] Ideally, the number of injected electrons and holes is equal, and both recombine at the interface. Setting mobility conditions facilitates this balance: a first luminescent layer with high hole mobility ensures that holes can quickly replenish the interface, while a second luminescent layer with high electron mobility ensures that electrons can also quickly replenish the interface. Neither type of charge carrier accumulates excessively in its respective transport layer, but rather reaches a dynamic equilibrium at the interface. When the carrier balance is optimized, leakage current (unrecombined charge carriers) is minimized, and all injected charge participates in interface recombination, thus achieving the target brightness with minimal current density.

[0055] In another embodiment of this application, such as Figure 5 As shown, Figure 5 This is a schematic diagram of the absorption spectrum of a fluorescent dye, the emission spectrum of a phosphorescent dye, and the emission spectrum of a fluorescent dye provided in the embodiments of this application.

[0056] In the embodiments of this application, the normalized intensity value at the intersection of the absorption spectrum of the fluorescent dye and the emission spectrum of the phosphorescent dye is greater than or equal to 0.8 and less than or equal to 1. In this embodiment, the absorption band of the fluorescent dye and the emission band of the phosphorescent dye need to highly overlap, and the overlapping region needs to have high intensity. The phosphorescent emitter needs to excite the fluorescent dye through non-radiative energy transfer, i.e., phosphorescence-sensitized fluorescence, which requires the fluorescent dye to have strong absorption in the phosphorescence emission band. Therefore, Figure 5 The closer point A is to 1, the higher the energy transfer efficiency, and theoretically the larger the overlap integral. However, competitive absorption must be avoided. If point A is too small (<0.8), it means that most of the light from the phosphorescent dye cannot be effectively absorbed by the fluorescent dye, resulting in weak energy transfer. For example, the normalized intensity of point A can be 0.8, 0.82, 0.86, 0.88, 0.9, 0.94, 0.96, 0.98, or 1.

[0057] In a preferred implementation, the normalized intensity value at the intersection of the emission spectrum of the fluorescent dye and the emission spectrum of the phosphorescent dye is greater than or equal to 0.6 and less than or equal to 0.9. In this embodiment, the emission spectral intensities of the two dyes need to be at similar positions. Figure 5 The normalized intensity value at point B should not be too low (less than 0.6) or too high (greater than 0.9). A value of ≥0.6 at point B means that the two emission peaks have significant overlap, but a value of ≤0.9 ensures that they do not overlap almost completely. For example, the normalized intensity value at point B can be set to 0.6, 0.65, 0.7, 0.75, 0.8, 0.85 or 0.9.

[0058] In a preferred implementation, it is necessary to ensure that the phosphorescence spectrum is pure, without strong secondary peaks, and that the normalized intensity value at the shoulder peak of the phosphorescent dye's emission spectrum is less than 0.5.

[0059] In another embodiment of this application, the thickness of the first light-emitting layer ranges from 50 Å to 100 Å, and the thickness of the second light-emitting layer ranges from 150 Å to 200 Å. In this embodiment, the thickness of the first light-emitting layer determines the path length of hole transport and the position of the exciton generation region relative to the interface. If the first light-emitting layer is too thin, it cannot effectively accommodate hole injection and transport. If the first light-emitting layer is too thick, the distance between its second light-emitting layers will exceed the effective operating distance of FET transfer.

[0060] The inventors discovered that a thickness of 50 Å to 100 Å for the first light-emitting layer ensures that the exciton generation region is located at the interface between the first and second light-emitting layers. For example, the thickness of the first light-emitting layer can be 50 Å, 60 Å, 70 Å, 80 Å, 90 Å, or 100 Å.

[0061] If the thickness of the second light-emitting layer is less than 150 Å, the second light-emitting layer will not be able to fully absorb the energy transferred from the FET of the first light-emitting layer. However, if the thickness of the second light-emitting layer is greater than 200 Å, the fluorescent dye molecules will not be effectively sensitized. Therefore, the thickness of the second light-emitting layer needs to be set between 150 Å and 200 Å. For example, the thickness of the second light-emitting layer can be 150 Å, 160 Å, 170 Å, 180 Å, 190 Å or 200 Å.

[0062] In a preferred implementation, the doping concentration of the phosphorescent dye in the first emitting layer ranges from 8% to 12%, for example, it can be 8%, 9%, 10%, 11%, or 12%. The doping concentration can be a volume ratio, that is, the volume of the phosphorescent dye in the first emitting layer accounts for 8% to 12% of the volume of the first emitting layer.

[0063] In a preferred implementation, the doping concentration of the fluorescent dye in the second emitting layer ranges from 1% to 3%, for example, it can be 1%, 1.5%, 2%, 2.5%, or 3%. The doping concentration can be a volume ratio, that is, the volume of the fluorescent dye in the second emitting layer accounts for 1% to 3% of the volume of the second emitting layer.

[0064] For example, using a blue phosphorescent device with a single emitting layer structure in the prior art as a benchmark, the luminous efficiency and luminous lifetime of the blue light-emitting device with a double emitting layer structure in the embodiments of this application are compared and analyzed. Please refer to Table 1 for details. Table 1. Luminous efficiency and luminous lifetime of light-emitting devices with different structures

[0065] In Table 1, structure 11 is an OLED structure analyzed as a benchmark in related technologies. Its specific structure is a single light-emitting layer structure: anode / hole injection layer (10nm) / hole transport layer (15nm) / electron blocking layer (5nm) / first light-emitting layer (20nm) / hole blocking layer (5nm) / electron transport layer (10nm) / electron transport layer (30nm) / electron injection layer (2nm) / cathode (13nm). The doping concentration of the phosphorescent dye in the first light-emitting layer is 9%.

[0066] Unlike structure 11, structure 12 in Table 1 has a specific structure of a double-emitting layer, that is... Figure 3 The structure shown includes an anode / hole injection layer (10nm) / hole transport layer (15nm) / electron blocking layer (5nm) / first emitting layer (80Å) / second emitting layer (180Å) / hole blocking layer (5nm) / electron transport layer (10nm) / electron injection layer (2nm) / cathode (13nm). The first emitting layer comprises a first host material and a first guest material; the second emitting layer comprises a second host material and a second guest material. The first guest material is a phosphorescent dye, and the second guest material is a fluorescent dye. The HOMO level of the electron blocking layer is greater than the HOMO level of the first host material, with a difference of 0.3 eV. The LUMO level of the first host material is greater than the LUMO level of the second host material, with a difference of 0.2 eV. The doping concentration of the phosphorescent dye in the first emitting layer is 9%; the doping concentration of the fluorescent dye in the second emitting layer is 2%. Compared to structure 11, structure 12 additionally includes a second emitting layer; the rest of the structure is the same as structure 11.

[0067] Unlike structure 12, in structure 13 the HOMO energy level of the electron blocking layer is greater than the HOMO energy level of the first host material, with a level difference of 0.32 eV; the LUMO energy level of the first host material is greater than the LUMO energy level of the second host material, with a level difference of 0.25 eV; the rest of the settings are the same as those of structure 12.

[0068] Unlike structure 12, in structure 14, the HOMO energy level of the electron blocking layer is greater than the HOMO energy level of the first host material, with a level difference of 0.35 eV; the LUMO energy level of the first host material is greater than the LUMO energy level of the second host material, with a level difference of 0.3 eV; the rest of the settings are the same as those of structure 12.

[0069] Unlike structure 12, in structure 15 the HOMO energy level of the electron blocking layer is greater than the HOMO energy level of the first host material, with a level difference of 0.4 eV; the LUMO energy level of the first host material is greater than the LUMO energy level of the second host material, with a level difference of 0.38 eV; the rest of the settings are the same as in structure 12.

[0070] As shown in Table 1, when the blue light-emitting device adopts a dual-emitting-layer structure including a first emitting layer and a second emitting layer, the luminous efficiency of the organic electroluminescent device is increased by 19-26% and the luminous lifetime is increased by 22-28% compared with the single emitting-layer structure. The increase in luminous efficiency and luminous lifetime increases with the increase of the difference between the HOMO energy level of the electron blocking layer and the HOMO energy level of the first host material, and the difference between the LUMO energy level of the first host material and the LUMO energy level of the second host material.

[0071] This application also provides a display panel including the light-emitting device described in the above embodiments, wherein the display panel can be applied to electronic devices such as smartphones, tablets, or laptops.

[0072] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0073] The embodiments described above are merely illustrative of several implementation methods of this application, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the patent application. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of this application, and these all fall within the protection scope of this application. Therefore, the protection scope of this patent application should be determined by the appended claims.

Claims

1. A light-emitting device, characterized in that, include: A first electrode and a second electrode, wherein the first electrode and the second electrode are disposed opposite to each other and spaced apart from each other; A first light-emitting layer and a second light-emitting layer are disposed between the first electrode layer and the second electrode layer and are in contact with each other; the first light-emitting layer includes a first host material and a first guest material; the second light-emitting layer includes a second host material and a second guest material; the first guest material is a phosphorescent dye and the second guest material is a fluorescent dye; An electron blocking layer is located between the first electrode and the first light-emitting layer; The HOMO energy level of the electron blocking layer is greater than that of the first host material.

2. The light-emitting device according to claim 1, characterized in that, The difference between the HOMO energy level of the electron blocking layer and the HOMO energy level of the first host material is greater than or equal to 0.3 eV and less than or equal to 0.4 eV.

3. The light-emitting device according to claim 1, characterized in that, The LUMO energy level of the first host material is greater than that of the second host material.

4. The light-emitting device according to claim 3, characterized in that, The difference between the LUMO energy level of the first host material and the LUMO energy level of the second host material is greater than or equal to 0.2 eV and less than or equal to 0.4 eV.

5. The light-emitting device according to claim 2, characterized in that, The triplet energy level of the electron blocking layer is greater than the triplet energy level of the first host material; And / or, the triplet energy level of the phosphorescent dye is lower than the triplet energy level of the first host material; And / or, the triplet energy level of the second host material is lower than the triplet energy level of the first host material.

6. The light-emitting device according to claim 1, characterized in that, The ratio of the electron mobility of the first host material to the electron mobility of the second host material is less than 1.

7. The light-emitting device according to claim 6, characterized in that, The ratio of the hole mobility of the first main material to the hole mobility of the second main material is greater than 1.

8. The light-emitting device according to claim 1, characterized in that, The normalized intensity value at the intersection of the absorption spectrum of the fluorescent dye and the emission spectrum of the phosphorescent dye is greater than or equal to 0.8 and less than or equal to 1. Preferably, the normalized intensity value at the intersection of the emission spectrum of the fluorescent dye and the emission spectrum of the phosphorescent dye is greater than or equal to 0.6 and less than or equal to 0.

9. Preferably, the normalized intensity value at the shoulder peak of the emission spectrum of the phosphorescent dye is less than 0.

5.

9. The light-emitting device according to any one of claims 1-8, characterized in that, The thickness of the first light-emitting layer ranges from 50 Å to 100 Å, and the thickness of the second light-emitting layer ranges from 150 Å to 200 Å. Preferably, the doping concentration of the phosphorescent dye in the first luminescent layer is in the range of 8%-12%; Preferably, the doping concentration of the fluorescent dye in the second luminescent layer is in the range of 1%-3%.

10. A display panel, characterized in that, The display panel includes the light-emitting device according to any one of claims 1-9.

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