Light emitting device and display panel

Abstract

The present disclosure provides a light-emitting device and a display panel, and belongs to the technical field of display. The light-emitting device comprises an anode, a cathode, and a light-emitting functional layer arranged between the anode and the cathode; the light-emitting functional layer comprises at least a light-emitting layer and a carrier blocking layer; the light-emitting layer comprises a first host material, a first phosphorescent guest material and a light-emitting guest material; the carrier blocking layer comprises a second host material and a second phosphorescent guest material; the lowest singlet energy level of the second phosphorescent guest material is smaller than the lowest singlet energy level of the first phosphorescent guest material, and the lowest singlet energy level of the second phosphorescent guest material is larger than the lowest singlet energy level of the light-emitting guest material; the lowest triplet energy level of the second phosphorescent guest material is smaller than the lowest triplet energy level of the first phosphorescent guest material, and the lowest triplet energy level of the second phosphorescent guest material is larger than the lowest triplet energy level of the light-emitting guest material.

Description

Technical Field

[0001] This disclosure belongs to the field of display technology, specifically relating to a light-emitting device and a display panel. Background Technology

[0002] Organic light-emitting diodes (OLEDs) are electroluminescent devices widely used in display technology and lighting. They work by injecting current into organic materials, which causes electrons and holes to recombine to form excitons and emit light. Summary of the Invention

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

[0004] Firstly, the technical solution adopted to solve the technical problem of this disclosure is a light-emitting device, including an anode, a cathode, and a light-emitting functional layer disposed between the anode and the cathode; the light-emitting functional layer includes at least a light-emitting layer and a carrier blocking layer;

[0005] The light-emitting layer comprises a first host material, a first phosphorescent guest material, and a light-emitting guest material; the carrier blocking layer comprises a second host material and a second phosphorescent guest material.

[0006] The lowest singlet state energy level of the second phosphorescent guest material is lower than that of the first phosphorescent guest material, and the lowest singlet state energy level of the second phosphorescent guest material is higher than that of the luminescent guest material; the lowest triplet state energy level of the second phosphorescent guest material is lower than that of the first phosphorescent guest material, and the lowest triplet state energy level of the second phosphorescent guest material is higher than that of the luminescent guest material.

[0007] In some embodiments, the lowest singlet state energy level of the second host material is lower than the lowest singlet state energy level of the first phosphorescent guest material, and the lowest singlet state energy level of the second host material is higher than the lowest singlet state energy level of the luminescent guest material; the lowest triplet state energy level of the second host material is lower than the lowest triplet state energy level of the first phosphorescent guest material, and the lowest triplet state energy level of the second host material is higher than the lowest triplet state energy level of the luminescent guest material.

[0008] In some embodiments, the lowest singlet state energy level of the second host material is greater than the lowest singlet state energy level of the second phosphorescent guest material; the lowest triplet state energy level of the second host material is greater than the lowest triplet state energy level of the second phosphorescent guest material.

[0009] In some embodiments, the lowest singlet state energy level of the first host material is greater than the lowest singlet state energy level of the first phosphorescent guest material; the lowest triplet state energy level of the first host material is greater than the lowest triplet state energy level of the first phosphorescent guest material.

[0010] The lowest singlet energy level of the first phosphorescent guest material is greater than the lowest triplet energy level of the first phosphorescent guest material.

[0011] In some embodiments, the first host material includes a hole-type host material and an electronic-type host material.

[0012] In some embodiments, the difference between the lowest triplet energy level of the first phosphorescent guest material and the lowest triplet energy level of the second phosphorescent guest material is less than or equal to 0.3 eV; and / or,

[0013] The difference between the lowest triplet energy level of the second phosphorescent guest material and the lowest triplet energy level of the luminescent guest material is less than or equal to 0.3 eV.

[0014] In some embodiments, the difference between the lowest triplet energy level of the second phosphorescent guest material and the lowest triplet energy level of the luminescent guest material is less than the difference between the lowest singlet energy level of the second phosphorescent guest material and the lowest triplet energy level of the second phosphorescent guest material.

[0015] In some embodiments, the difference between the lowest singlet state energy level and the lowest triplet state energy level of the luminescent guest material is less than or equal to 0.3 eV.

[0016] In some embodiments, the photoluminescence spectrum of the first phosphorescent guest material overlaps with the absorption spectrum of the second phosphorescent guest material, and the overlapping wavelength range is between 420 nm and 460 nm.

[0017] The photoluminescence spectrum of the second phosphorescent guest material overlaps with the absorption spectrum of the luminescent guest material, and the overlapping wavelength range is between 420 nm and 460 nm.

[0018] In some embodiments, the doping ratio of the first phosphorescent guest material is between 5% and 15%; the doping ratio of the first phosphorescent guest material refers to the ratio of the mass of the first phosphorescent guest material to the total mass of the light-emitting layer;

[0019] The doping ratio of the luminescent guest material is between 0.5% and 5%; the doping ratio of the luminescent guest material refers to the ratio of the mass of the luminescent guest material to the total mass of the luminescent layer.

[0020] The doping ratio of the second phosphorescent guest material is between 1% and 8%; the doping ratio of the second phosphorescent guest material refers to the ratio of the mass of the second phosphorescent guest material to the total mass of the carrier blocking layer.

[0021] In some embodiments, the first host material includes a hole-type host material and an electronic-type host material;

[0022] The highest occupied molecular orbital (HOMO) energy level of the hole-type host material is between -5.8 eV and -6.1 eV, and the lowest unoccupied molecular orbital (LUMO) energy level of the hole-type host material is between -2.2 eV and -2.6 eV.

[0023] The HOMO energy level of the electronic host material is between -5.9 eV and -6.4 eV, and the LUMO energy level of the electronic host material is between -2.7 eV and -2.9 eV.

[0024] The HOMO energy level of the first phosphorescent guest material is between -5.4 eV and -5.8 eV, and the LUMO energy level of the first phosphorescent guest material is between -1.9 eV and -2.2 eV.

[0025] The HOMO energy level of the luminescent guest material is between -5.6 eV and -5.9 eV, and the LUMO energy level of the luminescent guest material is between -2.8 eV and -3.1 eV.

[0026] In some embodiments, the HOMO energy level of the second host material is between -5.7 eV and -6.0 eV, and the LUMO energy level of the second host material is between -2.3 eV and -2.7 eV;

[0027] The HOMO energy level of the second phosphorescent guest material is between -5.5 eV and -5.9 eV, and the LUMO energy level of the second phosphorescent guest material is between -2.0 eV and -2.4 eV.

[0028] In some embodiments, the carrier blocking layer includes an electron blocking layer disposed on the side of the light-emitting layer near the anode, and / or a hole blocking layer disposed on the side of the light-emitting layer near the cathode.

[0029] Secondly, embodiments of this disclosure also provide a display panel, including a light-emitting device as described in any one of the first aspects. Attached Figure Description

[0030] Figure 1 This is a schematic diagram illustrating energy transfer within the emissive layer of a blue phosphorescent OLED device, which is an example of this disclosure.

[0031] Figure 2This is a schematic diagram of the structure of a light-emitting device provided in an embodiment of the present disclosure.

[0032] Figure 3 This is a schematic diagram of energy transfer within the light-emitting layer of a light-emitting device provided in an embodiment of this disclosure.

[0033] Figure 4 This is a schematic diagram showing the cross-over of the photoluminescence spectrum of the first phosphorescent guest and the absorption spectrum of the second phosphorescent guest provided in an embodiment of this disclosure.

[0034] Figure 5 This is a schematic diagram showing the cross-over between the photoluminescence spectrum of the second phosphorescent guest material and the absorption spectrum of the luminescent guest material provided in the embodiments of this disclosure.

[0035] Figure 6 This is a schematic diagram of the light-emitting mechanism of the light-emitting device provided in Example 1, which is an embodiment of this disclosure.

[0036] Figure 7 This is a schematic diagram of the light-emitting mechanism of the light-emitting device provided in Example 2 of this disclosure.

[0037] Figure 8 This is a schematic diagram of the light-emitting mechanism of the light-emitting device provided in Example 3 of this disclosure.

[0038] Figure 9 This is a schematic diagram of the structure of a series light-emitting device provided in an embodiment of this disclosure. Detailed Implementation

[0039] 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 a part of the embodiments of this disclosure, and not all of them. The components of the embodiments of this disclosure described and shown in the accompanying drawings can generally be arranged and designed in various different configurations. Therefore, the following detailed description of the embodiments of this disclosure provided in the accompanying drawings is not intended to limit the scope of the claimed disclosure, but merely represents selected embodiments of this disclosure. All other embodiments obtained by those skilled in the art based on the embodiments of this disclosure without inventive effort are within the scope of protection of this disclosure.

[0040] Unless otherwise defined, the technical or scientific terms used in this disclosure shall have the ordinary meaning understood by one of ordinary skill in the art to which this disclosure pertains. The terms “first,” “second,” and similar terms used in this disclosure do not indicate any order, quantity, or importance, but are merely used to distinguish different components. Similarly, the terms “an,” “a,” or “the,” and similar terms do not indicate a quantity limitation, but rather indicate the presence of at least one. The terms “including,” “comprising,” or “containing,” and similar terms mean that the element or object preceding the word encompasses the elements or objects listed following the word and their equivalents, without excluding other elements or objects. The terms “connected,” “linked,” or similar terms are not limited to physical or mechanical connections, but can include electrical connections, whether direct or indirect. The terms “upper,” “lower,” “left,” and “right,” etc., are used only to indicate relative positional relationships, and these relative positional relationships may change accordingly when the absolute position of the described objects changes.

[0041] In this disclosure, "multiple or several" refers to two or more. "And / or" describes the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent: A alone, A and B simultaneously, or B alone. The character " / " generally indicates that the preceding and following related objects have an "or" relationship.

[0042] In related technologies, OLED devices mainly emit light in two ways: phosphorescence and fluorescence. The main difference lies in whether the guest material used in the light-emitting layer is a phosphorescent material or a fluorescent material.

[0043] For blue phosphorescent OLED devices, due to the characteristics of the light-emitting materials, there are problems such as long exciton lifetime, high triplet exciton concentration leading to triplet-triplet annihilation (TTA) effect and material decomposition, resulting in severe efficiency roll-off and poor device lifetime at high brightness. Figure 1 This is a schematic diagram illustrating energy transfer within the emissive layer of an exemplary blue phosphorescent OLED device of this disclosure, as shown below. Figure 1As shown, the emissive layer of a blue phosphorescent OLED device comprises a host material, a phosphorescent guest material (such as a sensitizer), and an emissive guest material (such as thermally activated delayed fluorescence (TADF) material). Under the influence of an electric field, charge carriers are injected through electrodes and then transported to the emissive layer via the charge carrier transport layer, forming singlet and triplet excitons on the host material. Energy is then transferred to the phosphorescent guest material via Förster energy transfer (FRET, primarily responsible for the energy transfer of singlet excitons) and Dexter energy transfer (DET, also known as electron exchange excitation transfer, primarily responsible for the transfer of triplet excitons). The strong spin-orbit coupling of phosphorescent guest materials results in considerable dipole strength during donor triplet-acceptor singlet transitions, enabling the triplet state to undergo the FRET mechanism. This means that triplet excitons are transferred to the luminescent guest material's singlet state via Förster energy transfer; simultaneously, some triplet excitons also transfer energy to the luminescent guest material's triplet state via Dexter energy transfer. The singlet excitons in the luminescent guest material emit light through rapid radiative decay. Similarly, some singlet excitons are converted to triplet states via intersystem crossing (ISC). Furthermore, the luminescent guest material allows for the conversion of non-radiative triplet states to radiative singlet states via reverse intersystem crossing (RISC), theoretically achieving 100% internal quantum efficiency (IQE).

[0044] However, on the one hand, phosphorescent guest materials transfer triplet excitons to the triplet state of the luminescent guest material via Dexter energy transfer, and the luminescent guest material also converts singlet excitons into triplet states via intersystem crossing (ISC). However, the energy transfer efficiency of reverse intersystem crossing (RISC) is low, which easily leads to the accumulation of triplet excitons and the loss of nonradiative (tritt exciton) energy. On the other hand, the narrow exciton recombination region within the luminescent layer also leads to an excessively high concentration of triplet excitons, which cannot be dissipated in time. Their high energy causes severe triplet-tritt annihilation (TTA) and triplet-polaron annihilation (TPA) during collisions and recombination, resulting in the generation of excitons and polarons with even higher energies. These high-energy excitons can break the chemical bonds of organic materials, leading to material degradation, which in turn causes a severe roll-off in device efficiency and a shortened device lifespan at high brightness.

[0045] In view of this, the present disclosure provides a light-emitting device and a display panel, aiming to solve the technical problem in existing phosphorescent OLED devices where the excessively high concentration of triplet excitons in the light-emitting layer, which cannot be dissipated in time, leads to severe triplet-triplet annihilation (TTA) and triplet-polaron annihilation (TPA), resulting in a severe efficiency roll-off and shortened device lifetime at high brightness. This disclosure constructs a bidirectional exciton energy transport channel by doping a second phosphorescent guest material with a specific energy level structure into the carrier blocking layer. This enables the transient storage and secondary utilization of excess triplet excitons in the light-emitting layer, significantly improving the overall exciton utilization rate and effectively suppressing the exciton annihilation process, thereby maintaining high luminous efficiency while greatly extending the device's lifespan.

[0046] Figure 2 This is a schematic diagram of the structure of a light-emitting device provided in an embodiment of the present disclosure. Figure 3 This is a schematic diagram of energy transfer within the light-emitting layer of a light-emitting device provided in an embodiment of this disclosure, as shown below. Figure 2 and Figure 3 As shown, the light-emitting device includes an anode 1, a cathode 2, and a light-emitting functional layer 3 disposed between the anode 1 and the cathode 2; the light-emitting functional layer 3 includes at least a light-emitting layer EML and a carrier blocking layer 31. Exemplarily, the light-emitting functional layer 3 includes, sequentially arranged from the anode 1 towards the cathode 2, a hole injection layer HIL, a hole transport layer HTL, an electron blocking layer EBL, the light-emitting layer EML, the hole blocking layer HBL, the electron transport layer ETL, and the electron injection layer EIL. The hole injection layer HIL is used to rapidly inject holes generated by the anode 1 into the hole transport layer HTL. The hole transport layer HTL is used to efficiently transport holes to the electron blocking layer EBL. The electron blocking layer EBL is mainly used to block electrons and transport holes to the light-emitting layer EML. The electron injection layer EIL is used to rapidly inject electrons generated by the cathode 2 into the electron transport layer ETL. The electron transport layer ETL is used to efficiently transport electrons to the hole blocking layer HBL. The hole blocking layer HBL is mainly used to block holes and transport electrons to the light-emitting layer EML. The luminescent layer (EML) promotes the recombination of holes and electrons to form excitons and emit light.

[0047] The carrier blocking layer 31 is in direct contact with the light-emitting layer EML. Optionally, the carrier blocking layer 31 can be an electron blocking layer EBL and / or a hole blocking layer HBL.

[0048] The luminescent layer EML comprises a first host material, a first phosphorescent guest material, and a luminescent guest material; the carrier blocking layer 31 comprises a second host material and a second phosphorescent guest material. Optionally, the first phosphorescent guest material is a photosensitizer; the second phosphorescent guest material is a photosensitizer. The luminescent guest material is a thermally activated delayed fluorescence (TADF) material.

[0049] The lowest singlet state energy level (S1) of the second phosphorescent guest material is lower than that of the first phosphorescent guest material, and the lowest singlet state energy level (S1) of the second phosphorescent guest material is higher than that of the luminescent guest material; that is, S1 (luminescent guest material) < S1 (second phosphorescent guest material) < S1 (first phosphorescent guest material). The lowest triplet state energy level (T1) of the second phosphorescent guest material is lower than that of the first phosphorescent guest material, and the lowest triplet state energy level of the second phosphorescent guest material is higher than that of the luminescent guest material; that is, T1 (luminescent guest material) < T1 (second phosphorescent guest material) < T1 (first phosphorescent guest material). In this way, triplet excitons from the first phosphorescent guest material can be transferred to the triplet state of the second phosphorescent guest material via Dexter energy transfer. The second phosphorescent guest material can receive and store triplet excitons, serving as an exciton energy buffer layer. Simultaneously, triplet excitons from the second phosphorescent guest material can be transferred back to the triplet state of the luminescent guest material via Dexter energy transfer, forming a bidirectional exciton energy transmission channel. This enables the transient storage and secondary utilization of excess triplet excitons within the luminescent EML, significantly improving the utilization rate of triplet excitons within the luminescent EML, effectively suppressing triplet-triplet exciton annihilation (TTA), reducing exciton loss, and significantly improving device efficiency and lifetime.

[0050] Furthermore, through the doping design of the carrier blocking layer 31 described above, the exciton recombination and energy exchange region of this disclosure is no longer limited to the interior of the emissive layer EML, but extends to the adjacent carrier blocking layer 31 region. The second phosphorescent guest material serves as an exciton buffer, allowing the high concentration of triplet excitons, originally concentrated in the narrow region of the emissive layer EML, to be spatially dispersed. This widening of the exciton recombination region effectively reduces the exciton density per unit volume, fundamentally reducing the probability of triplet excitons annihilating upon encountering each other, suppressing the TTA effect, thereby improving the efficiency roll-off phenomenon of the device at high current densities, and enabling the device to maintain stable luminescence performance over a wide brightness range.

[0051] Furthermore, by using a second phosphorescent guest material to transiently store excess triplet excitons, the long-term, high-concentration accumulation of excitons within the emissive layer (EML) is avoided. This not only reduces the instantaneous energy loss caused by TTA (transient energy transfer), but more importantly, it reduces the TPA (transient energy transfer effect) induced by the interaction between high-energy excitons and polarons, as well as the resulting problems of molecular bond breaking and aging in organic materials. By effectively suppressing these non-radiative processes that accelerate device aging, the degradation rate of the EML material under high electric fields is significantly reduced. This results in a substantial extension of the lifespan of the blue phosphorescent OLED device while maintaining high luminous efficiency, particularly with a significant improvement in long-term stability under high brightness conditions.

[0052] In some embodiments, the lowest singlet state energy level (S1) of the second host material is lower than the lowest singlet state energy level (S1) of the first phosphorescent guest material, and the lowest singlet state energy level of the second host material is higher than the lowest singlet state energy level (S1) of the luminescent guest material; the lowest triplet state energy level (T1) of the second host material is lower than the lowest triplet state energy level (T1) of the first phosphorescent guest material, and the lowest triplet state energy level (T1) of the second host material is higher than the lowest triplet state energy level (T1) of the luminescent guest material.

[0053] That is, S1 (luminescent guest material) < S1 (second host material) < S1 (first phosphorescent guest material); T1 (luminescent guest material) < T1 (second host material) < T1 (first phosphorescent guest material).

[0054] This specific energy level arrangement allows triplet excitons, which might otherwise diffuse to the edge of the emissive layer (EML) and be lost, to be effectively captured and temporarily stored by the second phosphorescent guest material. These excitons are then transferred back to the emissive guest material in the EML via a reverse energy transfer process, enabling them to participate in luminescence again. This design breaks the limitation of unidirectional exciton transfer in traditional structures, significantly improving the overall utilization rate of triplet excitons and reducing non-radiative dissipation of excitons at the interface.

[0055] Furthermore, the lowest singlet state energy level (S1) of the second host material is greater than the lowest singlet state energy level (S1) of the second phosphorescent guest material; the lowest triplet state energy level (T1) of the second host material is greater than the lowest triplet state energy level (T1) of the second phosphorescent guest material, that is, S1 (second phosphorescent guest material) < S1 (second host material), T1 (second phosphorescent guest material) < T1 (second host material), so as to ensure that excitons in the carrier blocking layer 31 can be effectively captured by the second phosphorescent guest material, rather than quenched by the second host material, thereby ensuring exciton utilization.

[0056] In summary, S1 (luminescent guest material) < S1 (second phosphorescent guest material) < S1 (second host material) < S1 (first phosphorescent guest material); T1 (luminescent guest material) < T1 (second phosphorescent guest material) < T1 (second host material) < T1 (first phosphorescent guest material). This disclosure optimizes the spatiotemporal distribution of excitons within the OLED device by precisely controlling the energy level matching relationship between the carrier blocking layer 31 material and the luminescent layer EML material, particularly by utilizing the second phosphorescent guest material as an exciton energy buffer layer. This forms an efficient cascaded energy transfer system with the first phosphorescent guest material and the luminescent guest material within the luminescent layer EML, effectively avoiding non-radiative dissipation of excitons at the luminescent layer EML interface.

[0057] In some embodiments, such as Figure 3As shown, the lowest singlet state energy level (S1) of the first host material is greater than that of the first phosphorescent guest material (S1); the lowest triplet state energy level (T1) of the first host material is greater than that of the first phosphorescent guest material (T1). That is, S1 (first phosphorescent guest material) < S1 (first host material); T1 (first phosphorescent guest material) < T1 (first host material). Thus, singlet excitons of the first host material can be transferred to the singlet state of the first phosphorescent guest material via Förster energy transfer, and triplet excitons of the first host material can be transferred to the triplet state of the first phosphorescent guest material via Dexter energy transfer.

[0058] Furthermore, the lowest singlet state energy level (S1) of the first phosphorescent guest material is greater than the lowest triplet state energy level (T1) of the first phosphorescent guest material. Thus, at least some of the singlet excitons of the first phosphorescent guest material are converted into triplet states through intersystem transitions (ISC), which is beneficial to improving the utilization rate of triplet excitons in the emissive layer EML.

[0059] The lowest singlet state energy level (S1) of the first host material is greater than the lowest triplet state energy level (T1) of the first host material. Optionally, the first host material includes a hole-type host material (P-host) and an electron-type host material (N-host).

[0060] The lowest singlet state energy level (S1) of the luminescent guest material is greater than the lowest triplet state energy level (T1) of the luminescent guest material. The lowest singlet state energy level (S1) of the second phosphorescent guest material is greater than the lowest triplet state energy level (T1) of the second phosphorescent guest material.

[0061] In some embodiments, the difference between the lowest triplet energy level (T1) of the first phosphorescent guest material and the lowest triplet energy level (T1) of the second phosphorescent guest material is less than or equal to 0.3 eV. That is, T1 (first phosphorescent guest material) - T1 (second phosphorescent guest material) ≤ 0.3 eV, ensuring that triplet excitons can be efficiently transferred from the first phosphorescent guest material to the second phosphorescent guest material via Dexter energy transfer, thereby achieving transient storage of triplet excitons.

[0062] In some embodiments, the difference between the lowest triplet energy level (T1) of the second phosphorescent guest material and the lowest triplet energy level (T1) of the luminescent guest material is less than or equal to 0.3 eV. That is, T1 (second phosphorescent guest material) - T1 (luminescent guest material) ≤ 0.3 eV, ensuring that triplet excitons can be efficiently transferred from the second phosphorescent guest material to the luminescent guest material via Dexter energy transfer, thereby achieving efficient utilization of triplet excitons.

[0063] Furthermore, the difference between the lowest triplet energy level (T1) of the second phosphorescent guest material and the lowest triplet energy level (T1) of the luminescent guest material is less than the difference between the lowest singlet energy level (S1) of the second phosphorescent guest material and the lowest triplet energy level (T1) of the second phosphorescent guest material. That is, T1 (second phosphorescent guest material) - T1 (luminescent guest material) < S1 (second phosphorescent guest material) - T1 (second phosphorescent guest material). Thus, radiative transitions or non-radiative dissipation of excitons in the second phosphorescent guest material can be suppressed.

[0064] In some embodiments, the difference between the lowest singlet state energy level (S1) and the lowest triplet state energy level (T1) of the luminescent guest material is less than or equal to 0.3 eV. That is, S1 (luminescent guest material) - T1 (luminescent guest material) ≤ 0.3 eV. This allows the triplet excitons received by the luminescent guest material to be rapidly converted into singlet excitons through a reverse systematic crossover (RISC) process, thereby achieving radiative transition luminescence and ensuring that the guest luminescent material can emit light efficiently.

[0065] In some embodiments, Figure 4 This is a schematic diagram showing the overlap between the photoluminescence spectrum of the first phosphorescent guest and the absorption spectrum of the second phosphorescent guest provided in an embodiment of this disclosure, as shown below. Figure 4 As shown, the photoluminescence spectrum of the first phosphorescent guest material overlaps with the absorption spectrum of the second phosphorescent guest material, with the overlap wavelength ranging from 420 nm to 460 nm. Measurements show that the overlap area between the photoluminescence and absorption spectra of the first and second phosphorescent guest materials accounts for 10% to 35% of the total photoluminescence spectrum area of ​​the first phosphorescent guest material, thus ensuring that triplet excitons can be effectively transferred from the first to the second phosphorescent guest material.

[0066] Figure 5 This is a schematic diagram showing the overlap between the photoluminescence spectrum of the second phosphorescent guest material and the absorption spectrum of the luminescent guest material provided in the embodiments of this disclosure, as shown below. Figure 5 As shown, the photoluminescence spectrum of the second phosphorescent guest material overlaps with the absorption spectrum of the luminescent guest material, with the overlap wavelength ranging from 420 nm to 460 nm. Measurements show that the overlap area between the photoluminescence spectrum of the second phosphorescent guest material and the absorption spectrum of the luminescent guest material accounts for 10% to 50% of the total photoluminescence spectrum area of ​​the second phosphorescent guest material, thus ensuring that triplet excitons can be effectively transported back from the second phosphorescent guest material to the luminescent guest material.

[0067] In some embodiments, the doping ratio of the first phosphorescent guest material is between 5% and 15%; the doping ratio of the first phosphorescent guest material refers to the ratio of the mass of the first phosphorescent guest material to the total mass of the emissive layer EML. For example, the doping ratio of the first phosphorescent guest material is 5%, 10%, or 15%.

[0068] The doping ratio of the luminescent guest material is between 0.5% and 5%; the doping ratio of the luminescent guest material refers to the ratio of the mass of the luminescent guest material to the total mass of the luminescent layer (EML). For example, the doping ratio of the luminescent guest material is 0.5%, 1%, 2%, 2.5%, 3%, 4%, or 5%.

[0069] Optionally, the doping ratio of the luminescent guest material is less than that of the first phosphorescent guest material.

[0070] The doping ratio of the second phosphorescent guest material is between 1% and 8%; the doping ratio of the second phosphorescent guest material refers to the ratio of the mass of the second phosphorescent guest material to the total mass of the carrier blocking layer 31. For example, the doping ratio of the second phosphorescent guest material is 1%, 2%, 3%, 4%, 5%, 6%, 7%, or 8%. The design range of the doping ratio of the second phosphorescent guest material in this disclosure can ensure the effective capture of diffused excitons by the second phosphorescent guest material, while avoiding unnecessary radiative transitions or concentration quenching of excitons in the carrier blocking layer 31 caused by excessively high doping concentration.

[0071] In some embodiments, the first host material includes a hole-type host material (P-host) and an electronic host material (N-host).

[0072] The highest occupied molecular orbital (HOMO) energy level of the hole-type host material P-host is between -5.8 eV and -6.1 eV, while the lowest unoccupied molecular orbital (LUMO) energy level of the hole-type host material P-host is between -2.2 eV and -2.6 eV.

[0073] The HOMO level of the electronic host material N-host is between -5.9 eV and -6.4 eV, while the LUMO level is between -2.7 eV and -2.9 eV.

[0074] The HOMO energy level of the first phosphorescent guest material is between -5.4 eV and -5.8 eV, and the LUMO energy level of the first phosphorescent guest material is between -1.9 eV and -2.2 eV.

[0075] The HOMO energy level of the luminescent guest material is between -5.6 eV and -5.9 eV, while the LUMO energy level of the luminescent guest material is between -2.8 eV and -3.1 eV.

[0076] The HOMO energy level of the second host material is between -5.7 eV and -6.0 eV, and the LUMO energy level of the second host material is between -2.3 eV and -2.7 eV.

[0077] The HOMO energy level of the second phosphorescent guest material is between -5.5 eV and -5.9 eV, and the LUMO energy level of the second phosphorescent guest material is between -2.0 eV and -2.4 eV.

[0078] This disclosure strictly limits the energy level parameters of the various functional materials involved in the luminescent layer EML and the adjacent carrier blocking layer 31 to ensure that an efficient exciton storage and reverse transfer mechanism is achieved between the luminescent layer EML and the adjacent carrier blocking layer 31.

[0079] In some embodiments, the carrier blocking layer 31 includes an electron blocking layer EBL disposed on the side of the light-emitting layer EML near the anode 1, and / or a hole blocking layer HBL disposed on the side of the light-emitting layer EML near the cathode 2.

[0080] For example, Figure 6 This is a schematic diagram of the light-emitting mechanism of the light-emitting device provided in Example 1 of the embodiments of this disclosure, as shown below. Figure 6 As shown, the light-emitting device can be a blue phosphorescent OLED device based on a sensitization system. Its structure sequentially includes: an anode 1, a hole injection layer HIL, a hole transport layer HTL, an electron blocking layer EBL, a light-emitting layer EML, a hole blocking layer HBL, an electron transport layer ETL, an electron injection layer EIL, and a cathode 2. The light-emitting layer EML is a single-layer structure, formed by co-evaporation of a hole-type host material (P-host), an electron-type host material (N-host), a first phosphorescent guest material (PtBD), and a light-emitting guest material (TADF). The hole blocking layer HBL is doped with a second phosphorescent guest material (PtBD), which receives and stores triplet excitons from the first phosphorescent guest material in the light-emitting layer EML and then transmits them back to the light-emitting guest material (TADF) for light emission.

[0081] The hole injection layer HIL can be made of inorganic oxides, such as molybdenum oxide, titanium oxide, vanadium oxide, rhenium oxide, ruthenium oxide, chromium oxide, zirconium oxide, hafnium oxide, tantalum oxide, silver oxide, tungsten oxide, and manganese oxide. Alternatively, the hole injection layer HIL can be made of p-type dopants and hole transport materials with strong electron-withdrawing systems, such as hexacyanohexaazatriphenylene, 2,3,5,6-tetrafluoro-7,7,8,8-tetracyano-p-quinone dimethyl ether (F4TCNQ), and 1,2,3-tris[(cyano)(4-cyano-2,3,5,6-tetrafluorophenyl)methylene]cyclopropane, etc.

[0082] The materials for the hole transport layer (HTL) and the electron blocking layer (EBL) (specifically, the second main material) can be the same or different materials. The materials of the hole transport layer (HTL) and / or the electron blocking layer (EBL) (specifically, the second host material) can be aromatic amines or carbazole materials with hole transport properties, such as 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-phenylfluorene-9-yl)triphenylamine (BAFLP), 4,4'-bis[N-(9,9-dimethylfluorene-2-yl)-N-phenylamino]biphenyl (DFLDPBi), 4,4'-bis(9-carbazolyl)biphenyl (CBP), 9-phenyl-3-[4-(10-phenyl-9-anthrayl)phenyl]-9H-carbazole (PCzPA), etc.

[0083] The luminescent layer (EML) comprises four materials co-deposited: a hole-host material (P-host), an electron-host material (N-host), a blue phosphorescent guest material (sensitizer), and a TADF guest material. The hole-host material (P-host) can be a material with high hole mobility, and its structure can include carbazole derivatives, aromatic amine derivatives, such as 4,4'-bis(N-carbazolyl)-1,1'-biphenyl (CBP), or TCTA (4,4',4''-tris(carbazol-9-yl)triphenylamine). The electron-host material (N-host) can be a material with high electron mobility, and its structure can include triazine, oxadiazole, or phenanthroline derivatives. For example, TPBi (1,3,5-tris(1-phenyl-1H-benzimidazol-2-yl)benzene), diphenyltriazine, etc. The blue phosphorescent guest material can be a metal complex, or a complex of iridium (Ir) and platinum (Pt). These materials possess high phosphorescence quantum efficiency and suitable triplet energy levels, making them suitable for blue emission. For example, blue phosphorescent guest materials include iridium complexes such as Firpic and Fir6, and platinum complexes such as PtOEP and PtON-TBBI. TADF guest materials can be donor-acceptor (DA) type molecules or multi-resonance TADF (MR-TADF) molecules, such as DACT-II, CzAcSF, ν-DABNA, and TBN-TPA.

[0084] The materials for the electron transport layer (ETL) and the hole blocking layer (HBL) (specifically, the second host material) can be the same or different materials. The materials for the ETL and / or the HBL (specifically, the second host material) can be aromatic heterocyclic compounds, such as imidazole derivatives, imidazopyridine derivatives, benzimidazole-phenanthridine derivatives, etc.; pyrimidine derivatives, triazine derivatives, etc.; quinoline derivatives, isoquinoline derivatives, phenanthreneline derivatives, etc., containing nitrogen-containing six-membered ring structures (including compounds with phosphine oxide substituents on the heterocycle); 2-(4-biphenyl)-5-(4-tert-butylphenyl)-1,3,4-oxadiazine 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-biphenyl)-1,2,4-triazole (TAZ), 3-(4-tert-butylphenyl)-4-(4-ethylphenyl)-5-(4-biphenyl)-1,2,4-triazole (p-EtTAZ), BPhen, BCP, 4,4'-bis(5-methylbenzoxazol-2-yl)stilbene (BzOs), etc.

[0085] The electron injection layer (EIL) can be made of alkali metal or alkaline earth metal compounds, such as lithium fluoride (LiF), cesium fluoride (CsF), sodium fluoride (NaF), potassium fluoride (KF), cesium oxide (Cs₂O), cesium carbonate (Cs₂CO₃), and lithium nitride (Li₃N). It can also be a low work function metal element, such as ytterbium (Yb), magnesium (Mg), calcium (Ca), or their alloy films. Furthermore, it can employ an n-type doping system, where a dopant with strong electron-donating ability is co-deposited with the electron transport material. For example, lithium (Li), cesium (Cs), or lithium nitride (Li₃N) can be doped into the electron transport material Alq₃ (tris(8-hydroxyquinoline)aluminum), BPhen (4,7-diphenyl-1,10-phenanthroline), or TmPyPB (1,3,5-tris(3-pyridyl-3-phenyl)benzene). The dopant provides electrons to the electron transport material, improving electron injection and transport capabilities.

[0086] The thickness ranges of the various films in the light-emitting functional layer 3 of this light-emitting device are different. For example, the thickness range of the hole injection layer HIL can be 0~3nm, the thickness range of the hole transport layer HTL can be 100nm~120nm, the thickness range of the electron blocking layer EBL can be 0~10nm, the thickness range of the light-emitting layer EML can be 20nm~40nm, the thickness range of the hole blocking layer HBL can be 0~10nm, the thickness range of the electron transport layer ETL can be 30nm~40nm, and the thickness range of the electron injection layer EIL can be 0~15nm. If the thickness of each layer varies within the above-mentioned thickness ranges, the color of the emitted light will vary within the same color system. It should be noted that the range values ​​disclosed herein can all be taken to their endpoints; however, in this example, at least one of the electron blocking layer EBL and the hole blocking layer HBL has a thickness that is not zero.

[0087] Optionally, such as Figure 2 As shown, the light-emitting device also includes a light extraction layer CPL disposed on the side of the cathode 2 away from the light-emitting functional layer 3, which is used to improve the light extraction efficiency.

[0088] For example, such as Figure 6 As shown, the film structure example from left to right is as follows: ITO / HTL:PD(0~3nm, 2%) / HTL(100nm~120nm) / EBL(0~10nm) / P-host:N-host:PtBD:TADF(10nm~20nm, 70%~90%:30~10%:10%~15%:1%~3%) / HBL:PtBD(0~10nm, 92%~99%:1%~8%) / ETL:LIQ(30nm~40nm(1:1)) / LIQ(0~15nm) / Mg:Ag(100nm~140nm, 2:8) / CPL. The molecular formulas of the compounds used in other functional layers are as follows.

[0089] HIL (PD): .

[0090] HTL: .

[0091] P-host: N-host: .

[0092] PtBD (first phosphorescent guest material): .

[0093] TADF (Light Emitting Material): .

[0094] HBL (Second Body Material): .

[0095] PtBD (second phosphorescent guest material): .

[0096] ETL: LIQ: .

[0097] Alternatively, the hole-type host material P-host can be used as the material for the electron blocking layer EBL.

[0098] For example, Figure 7 This is a schematic diagram of the light-emitting mechanism of the light-emitting device provided in Example 2 of the present disclosure, as shown below. Figure 7 As shown above, Figure 6 The difference is that the electron blocking layer (EBL) is doped with a second phosphorescent guest material, rather than the hole blocking layer (HBL).

[0099] For example, such as Figure 7 As shown, the following is an example of the film structure from left to right: ITO / HTL:PD(0~3nm, 2%) / HTL(100nm~120nm) / EBL:PtBD(0~10nm, 92%~99%: 1%~8%) / P-host:N-host:PtBD:TADF(10nm~20nm, 70%~90%: 30~10%: 10%~15%: 1%~3%) / HBL(0~10nm) / ETL:LIQ(30nm~40nm(1:1)) / LIQ(0~15nm) / Mg:Ag(100nm~140nm, 2:8) / CPL. The molecular formulas of the compounds used in other functional layers are as follows; those not shown can be found in the examples above.

[0100] EBL (Second Body Material): .

[0101] PtBD (second phosphorescent guest material): .

[0102] P-host: N-host: .

[0103] PtBD (first phosphorescent guest material): .

[0104] TADF (Light Emitting Material): .

[0105] Alternatively, the electronic host material N-host can be used as the material for the hole blocking layer HBL.

[0106] For example, Figure 8This is a schematic diagram of the light-emitting mechanism of the light-emitting device provided in Example 3 of the present disclosure, as shown below. Figure 8 As shown above, Figure 6 and Figure 7 The difference lies in the fact that both the hole blocking layer (HBL) and the electron blocking layer (EBL) are doped with a second phosphorescent guest material to maximize exciton storage and reverse propagation.

[0107] For example, such as Figure 8 As shown, the following is an example of the film structure from left to right: ITO / HTL:PD (0~3nm, 2%) / HTL (100nm~120nm) / EBL:PtBD (0~10nm, 92%~99%: 1%~8%) / P-host:N-host:PtBD:TADF (10nm~20nm, 70%~90%: 30~10%: 10%~15%: 1%~3%) / HBL:PtBD (0~10nm, 92%~99%: 1%~8%) / ETL:LIQ (30nm~40nm (1:1)) / LIQ (0~15nm) / Mg:Ag (100nm~140nm, 2:8) / CPL. The selection of the second host material and the second phosphorescent guest material in the electron blocking layer EBL is related to... Figure 7 The same example applies to the selection of the second phosphorescent guest material in the hole blocking layer (HBL). Figure 6 The example is the same; the selection of the second host material is as follows, and repeated parts will not be elaborated upon. The selection of the hole-type host material (P-host), the electron-type host material (N-host), the first phosphorescent guest material, and the luminescent guest material in the EML can be the same as... Figure 7 The same applies, and the repeated parts will not be repeated.

[0108] HBL (Second Body Material): .

[0109] Comparison and Figure 6 The difference in the example is that no second phosphorescent guest material is doped within the hole blocking layer HBL.

[0110] The performance comparison of the three light-emitting devices disclosed above with the comparative examples is shown in Table 1 below.

[0111] Table 1

[0112]

[0113] As can be seen, this disclosure significantly reduces efficiency roll-off at high brightness and significantly improves device efficiency and lifetime by doping the electron blocking layer EBL and / or hole blocking layer HBL with a second phosphorescent guest material having a specific energy level structure.

[0114] Furthermore, the device structure described above is also applicable to tandem light-emitting devices. Figure 9 This is a schematic diagram of the structure of the series light-emitting device provided in the embodiments of this disclosure, such as... Figure 9 As shown, for example, a series-connected light-emitting device includes an anode 1, a cathode 2, and a light-emitting unit 30 disposed between the anode 1 and the cathode 2, as well as a charge generation separation layer (CGL) disposed between adjacent light-emitting units. Exemplarily, the light-emitting unit 30 includes a first light-emitting unit 301 and a second light-emitting unit 302. The first light-emitting unit 301 is disposed on the side of the charge generation separation layer (CGL) near the anode 1. The first light-emitting unit 301 includes a hole injection layer HIL, a first hole transport layer HTL1, a first electron blocking layer EBL1, a first light-emitting layer EML1, a first hole blocking layer HBL1, and a first electron transport layer ETL1, arranged sequentially from the anode 1 towards the cathode 2; the second light-emitting unit 302 includes a second hole transport layer HTL2, a second electron blocking layer EBL2, a second light-emitting layer EML2, a second hole blocking layer HBL2, a second electron transport layer ETL2, and an electron injection layer EIL, arranged sequentially from the anode 1 towards the cathode 2. The charge generation separation layer (CGL) includes an N-type doped charge generation layer N-CGL and a P-type doped charge generation layer P-CGL. The N-type doped charge generation layer N-CGL is used to generate electrons, and the P-type doped charge generation layer P-CGL is used to generate holes.

[0115] The carrier blocking layer 31 can be at least one of the first electron blocking layer EBL1, the first hole blocking layer HBL1, the second electron blocking layer EBL2, and the second hole blocking layer HBL2.

[0116] The above is a complete description of the light-emitting device provided in the embodiments of this disclosure. The light-emitting device provided in the embodiments of this disclosure has the following characteristics: 1. Exciton storage-reverse propagation cycle mechanism: By doping a second phosphorescent guest material into the electron blocking layer EBL and / or hole blocking layer HBL, and utilizing its triplet energy level between the first phosphorescent guest material and the light-emitting guest material, an exciton temporary storage buffer pool is constructed to achieve the capture and reverse propagation of diffused excitons, breaking through the limitation of traditional unidirectional exciton propagation. 2. Spatial expansion of exciton recombination region: By doping the carrier blocking layer 31, exciton distribution extension bands are constructed on both sides of the light-emitting layer EML, extending the exciton recombination region from the interior of the light-emitting layer EML to the adjacent carrier blocking layer 31, reducing the local exciton concentration within the light-emitting layer EML, and suppressing the annihilation effect caused by excessively high exciton density from a spatial dimension. 3. By using the second phosphorescent guest material for transient storage and secondary distribution of triplet excitons, triplet excitons that might otherwise be lost through TTA or interface quenching are redirected to the luminescent guest material for luminescence, thereby improving the overall exciton utilization rate and reducing the aging damage of high-energy excitons to the material.

[0117] In addition, this disclosure also provides a display panel that includes the light-emitting device of any of the above embodiments. This display panel can be, for example, any product with a display function such as a mobile phone, tablet computer, television, monitor, laptop computer, digital photo frame, or in-vehicle device. Other essential components of this display device are understood by those skilled in the art and will not be described in detail here, nor should they be construed as limiting this disclosure.

[0118] It is understood that the above embodiments are merely exemplary embodiments used to illustrate the principles of this disclosure, and this disclosure is not limited thereto. For those skilled in the art, various modifications and improvements can be made without departing from the spirit and substance of this disclosure, and these modifications and improvements are also considered to be within the scope of protection of this disclosure.

Claims

1. A light-emitting device, characterized in that, It includes an anode, a cathode, and a light-emitting functional layer disposed between the anode and the cathode; the light-emitting functional layer includes at least a light-emitting layer and a carrier blocking layer; The light-emitting layer comprises a first host material, a first phosphorescent guest material, and a light-emitting guest material; the carrier blocking layer comprises a second host material and a second phosphorescent guest material. The lowest singlet state energy level of the second phosphorescent guest material is lower than that of the first phosphorescent guest material, and the lowest singlet state energy level of the second phosphorescent guest material is higher than that of the luminescent guest material; the lowest triplet state energy level of the second phosphorescent guest material is lower than that of the first phosphorescent guest material, and the lowest triplet state energy level of the second phosphorescent guest material is higher than that of the luminescent guest material.

2. The light-emitting device according to claim 1, characterized in that, The lowest singlet state energy level of the second host material is lower than that of the first phosphorescent guest material, and the lowest singlet state energy level of the second host material is higher than that of the luminescent guest material. The lowest triplet energy level of the second host material is lower than that of the first phosphorescent guest material, while the lowest triplet energy level of the second host material is higher than that of the luminescent guest material.

3. The light-emitting device according to claim 1, characterized in that, The lowest singlet state energy level of the second host material is greater than the lowest singlet state energy level of the second phosphorescent guest material; the lowest triplet state energy level of the second host material is greater than the lowest triplet state energy level of the second phosphorescent guest material.

4. The light-emitting device according to claim 1, characterized in that, The lowest singlet state energy level of the first host material is greater than the lowest singlet state energy level of the first phosphorescent guest material; the lowest triplet state energy level of the first host material is greater than the lowest triplet state energy level of the first phosphorescent guest material. The lowest singlet energy level of the first phosphorescent guest material is greater than the lowest triplet energy level of the first phosphorescent guest material.

5. The light-emitting device according to claim 4, characterized in that, The first host material includes a hole-type host material and an electronic-type host material.

6. The light-emitting device according to claim 1, characterized in that, The difference between the lowest triplet energy level of the first phosphorescent guest material and the lowest triplet energy level of the second phosphorescent guest material is less than or equal to 0.3 eV; and / or, The difference between the lowest triplet energy level of the second phosphorescent guest material and the lowest triplet energy level of the luminescent guest material is less than or equal to 0.3 eV.

7. The light-emitting device according to claim 1, characterized in that, The difference between the lowest triplet energy level of the second phosphorescent guest material and the lowest triplet energy level of the luminescent guest material is less than the difference between the lowest singlet energy level of the second phosphorescent guest material and the lowest triplet energy level of the second phosphorescent guest material.

8. The light-emitting device according to claim 1, characterized in that, The difference between the lowest singlet energy level and the lowest triplet energy level of the luminescent guest material is less than or equal to 0.3 eV.

9. The light-emitting device according to claim 1, characterized in that, The photoluminescence spectrum of the first phosphorescent guest material overlaps with the absorption spectrum of the second phosphorescent guest material, and the overlapping wavelength range is between 420 nm and 460 nm. The photoluminescence spectrum of the second phosphorescent guest material overlaps with the absorption spectrum of the luminescent guest material, and the overlapping wavelength range is between 420 nm and 460 nm.

10. The light-emitting device according to claim 1, characterized in that, The doping ratio of the first phosphorescent guest material is between 5% and 15%; the doping ratio of the first phosphorescent guest material refers to the ratio of the mass of the first phosphorescent guest material to the total mass of the light-emitting layer; The doping ratio of the luminescent guest material is between 0.5% and 5%; the doping ratio of the luminescent guest material refers to the ratio of the mass of the luminescent guest material to the total mass of the luminescent layer. The doping ratio of the second phosphorescent guest material is between 1% and 8%; the doping ratio of the second phosphorescent guest material refers to the ratio of the mass of the second phosphorescent guest material to the total mass of the carrier blocking layer.

11. The light-emitting device according to claim 1, characterized in that, The first host material includes hole-type host material and electron-type host material; The highest occupied molecular orbital (HOMO) energy level of the hole-type host material is between -5.8 eV and -6.1 eV, and the lowest unoccupied molecular orbital (LUMO) energy level of the hole-type host material is between -2.2 eV and -2.6 eV. The HOMO energy level of the electronic host material is between -5.9 eV and -6.4 eV, and the LUMO energy level of the electronic host material is between -2.7 eV and -2.9 eV. The HOMO energy level of the first phosphorescent guest material is between -5.4 eV and -5.8 eV, and the LUMO energy level of the first phosphorescent guest material is between -1.9 eV and -2.2 eV. The HOMO energy level of the luminescent guest material is between -5.6 eV and -5.9 eV, and the LUMO energy level of the luminescent guest material is between -2.8 eV and -3.1 eV.

12. The light-emitting device according to claim 1, characterized in that, The HOMO energy level of the second host material is between -5.7 eV and -6.0 eV, and the LUMO energy level of the second host material is between -2.3 eV and -2.7 eV. The HOMO energy level of the second phosphorescent guest material is between -5.5 eV and -5.9 eV, and the LUMO energy level of the second phosphorescent guest material is between -2.0 eV and -2.4 eV.

13. The light-emitting device according to any one of claims 1 to 12, characterized in that, The carrier blocking layer includes an electron blocking layer disposed on the side of the light-emitting layer near the anode, and / or a hole blocking layer disposed on the side of the light-emitting layer near the cathode.

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

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