To increase emission efficiency of a fluorescent light-emitting element by efficiently utilizing a triplet exciton generated in a light-emitting layer. The light-emitting layer of the light-emitting element includes at least a host material and a guest material. The triplet exciton generated from the host material in the light-emitting layer is changed to a singlet exciton by triplet-triplet annihilation (TTA). The guest material (fluorescent dopant) is made to emit light by energy transfer from the singlet exciton. Thus, the emission efficiency of the light-emitting element is improved.

Provided is a light-emitting element including a fluorescence-emitting material with high emission efficiency. The light-emitting element includes a pair of electrodes and an EL layer between the pair of electrodes. The EL layer includes a first organic compound, a second organic compound, and a guest material. The first organic compound has a function of emitting a thermally activated delayed fluorescence at room temperature. The guest material has a function of emitting fluorescence. A HOMO level of the first organic compound higher than or equal to a HOMO level of the second organic compound. A LUMO level of the first organic compound is lower than or equal to a LUMO level of the second organic compound.

An organic electroluminescent device and a display apparatus. The organic electroluminescent device includes a first electrode, a second electrode and an organic layer located between the first electrode and the second electrode. The organic layer includes a light-emitting layer. The light-emitting layer contains a host material, a thermally activated delayed fluorescence sensitizer and a fluorescent dye. The energy level relationship between the host material and the thermally activated delayed fluorescence sensitizer is LUMO.sub.host≥LUMO.sub.sensitizer, while HOMO.sub.sensitizer≥HOMO.sub.host.

An organic electroluminescent device and a display apparatus. The organic electroluminescent device includes a first electrode, a second electrode and at least two organic electroluminescent units located between the first electrode and the second electrode. The at least two organic electroluminescent units are arranged in a stacked manner. The at least two organic electroluminescent units include a first organic electroluminescent unit. The first organic electroluminescent unit includes a first light-emitting layer. The first light-emitting layer contains a first host material, a thermally activated delayed fluorescence sensitizer and a first fluorescent dye.

The embodiments of the present disclosure provide a light-emitting device and a display substrate, which belong to the technical field of organic light-emitting diodes. The light-emitting device of the present disclosure comprises: a first light-emitting layer comprising a first host material and a first guest material; and a second light-emitting layer comprising a second host material and a second guest material; S1(h1)>S1(g1), T1(h1)>T1(g1), S1(g1)−T1(g1)≤0.1 eV; S1(h2)>S1(g2), T1(h2)>T1(g2), S1(g2)−T1(g2)≤0.1 eV; S1(h1)≥S1(h2)>S1(g1)>S1(g2), T1(h1)≥T1(h2)>T1(g1)>T1(g2); the second guest material is a TADF material; at least 40% of the area in a region covered under the emission spectrum of the first light-emitting layer overlaps with the region covered under the absorption spectrum of the second light-emitting layer.

A light emitting material containing an adjustment compound N in addition to a donor compound D and an acceptor compound A that form an exciplex and satisfying HOMO(D)>HOMO(N)>HOMO(A), LUMO(D)>LUMO(N)+0.1 eV and LUMO(N)>LUMO(A) has improved luminous efficiency or emission lifetime.

The present disclosure belongs to the technical field of organic light-emitting diods (OLEDs), and provides a compound used as an electron transmission material of OLEDs. Molecules of the compounds include an aromatic ring (or aromatic fused ring) and a phenanthroline group that are connected to each other. In an embodiment, the compound according to the present disclosure includes two types of groups, i.e., an aromatic ring (or aromatic fused ring) and a phenanthroline (or benzoquinoline) group. These two groups not only have good electron accepting ability, but also can be well doped with metals. The planarity of the two groups is conducive to the stacking of molecules, which facilitates the combination of holes and electrons and generates excitons, thereby increasing the electron mobility of the material and improving efficiency of device.

A novel light-emitting device that is highly convenient, useful, or reliable is provided. The light-emitting device includes a first electrode, a second electrode, a unit, and a first layer. The second electrode includes a region overlapping with the first electrode. The unit includes a region positioned between the first electrode and the second electrode. The unit includes a second layer and a third layer. The second layer includes a region where the third layer is positioned between the second layer and the first electrode. The second layer contains a light-emitting material. The first layer includes a region positioned between the third layer and the first electrode. The first layer contains a material having an acceptor property and a first material. The first layer includes a first region and a second region. The first region includes a region positioned between the second region and the first electrode. The first region contains the material having an acceptor property at a first concentration. The second region contains the material having an acceptor property at a second concentration. Note that the second concentration is higher than zero and lower than the first concentration.

A light emitting diode of an embodiment of the present disclosure includes a first electrode, a hole transport region on an upper portion of the first electrode and having a first refractive index, an emission layer on an upper portion of the hole transport region and having a second refractive index less than the first refractive index, an electron transport region on an upper portion of the emission layer, and a second electrode on an upper portion of the electron transport region.

An electroluminescent device and a display device including the same. The electroluminescent device includes a first electrode and a second electrode facing each other; a light emitting layer disposed between the first electrode and the second electrode, the light emitting layer including a quantum dot; a hole transport layer disposed between the light emitting layer and the first electrode; and an electron transport layer disposed between the light emitting layer and the second electrode, wherein the hole transport layer, the light emitting layer, or a combination thereof includes thermally activated delayed fluorescence material, and the thermally activated delayed fluorescence material is present in an amount of greater than or equal to about 0.01 wt % and less than about 10 weight percent (wt %), based on 100 wt % of the hole transport layer, the light emitting layer, or the combination thereof including the thermally activated delayed fluorescence material.