JP-2026076235-A - Light-emitting element, light-emitting device, display device, electronic device, and lighting device

Abstract

[Problem] To provide a light-emitting element with high luminescence efficiency, which has a fluorescent light-emitting material. [Solution] The invention comprises a fluorescent light-emitting material and a host material, wherein the host material comprises a first organic compound and a second organic compound, the first organic compound and the second organic compound having the function of forming an excited complex, the luminescence exhibited by the excited complex having a delayed fluorescence component accounting for 5% or more, and the delayed fluorescence component has a fluorescence lifetime of 1 It has a delayed fluorescence component with a duration of 0 ns to 50 μs. [Selection Diagram] Figure 1

Inventors

• 石曽根 崇浩
• 細海 俊介
• 高橋 辰義
• 瀬尾 哲史

Assignees

• 株式会社半導体エネルギー研究所

Dates

Publication Date

20260511

Application Date

20260120

Priority Date

20150309

Claims (6)

1. Between a pair of electrodes, there is a first light-emitting layer, a second light-emitting layer, and a charge-generating layer. The charge generation layer is located between the first light-emitting layer and the second light-emitting layer. The charge generation layer has a configuration having a hole-transporting material and an acceptor material, a configuration having an electron-transporting material and a donor material, or a configuration in which a layer having a hole-transporting material and an acceptor material and a layer having an electron-transporting material and a donor material are laminated together. The first light-emitting layer of the present invention comprises a first organic compound and a first fluorescent light-emitting material. The T1 level of the first organic compound is lower than the T1 level of the first fluorescent material. The S1 level of the first organic compound is higher than the S1 level of the first fluorescent material. The second light-emitting layer comprises a thermally activated delayed fluorescence material having a delayed fluorescence component with a fluorescence lifetime of 10 ns to 50 μs, and exhibiting emission in which the proportion of the delayed fluorescence component is 5% or more, and a second fluorescent light-emitting material. The S1 level of the thermally activated delayed fluorescence material is higher than the S1 level of the second fluorescence emission material. The emission spectrum of the thermally activated delayed fluorescence material overlaps with the longest wavelength absorption band of the absorption spectrum of the second fluorescence emission material. The thermally activated delayed fluorescence material has the function of supplying excitation energy to the second fluorescence emission material. A light-emitting element that emits light from the first fluorescent material and light from the second fluorescent material.
2. In claim 1, The thermally activated delayed fluorescence material is a heterocyclic compound having a π-electron-rich heteroaromatic ring skeleton and a π-electron-deficient heteroaromatic ring skeleton, which is a light-emitting element.
3. A light-emitting device comprising a light-emitting element according to claim 1 or claim 2, and a substrate.
4. A display device comprising a light-emitting element according to claim 1 or claim 2, and at least one of a color filter or a transistor.
5. An electronic device comprising the display device described in claim 4 and at least one of a housing or a touch sensor.
6. A lighting device comprising a light-emitting element according to claim 1 or claim 2, and at least one of a housing or a touch sensor.

Description

One aspect of the present invention relates to a light-emitting element, or a display device, electronic device, and lighting device having the light-emitting element. It should be noted that one aspect of the present invention is not limited to the above-mentioned technical field. The technical field of one aspect of the invention disclosed herein relates to a product, a method, or a method of manufacture. Alternatively, one aspect of the present invention relates to a process, a machine, a manufacture, or a composition of matter. More specifically, examples of the technical field of one aspect of the present invention disclosed herein include semiconductor devices, display devices, liquid crystal display devices, light-emitting devices, lighting devices, energy storage devices, memory devices, methods for driving them, or methods for manufacturing them. In recent years, electroluminescence (EL) Research and development of light-emitting devices utilizing this technology are actively underway. The basic structure of these light-emitting devices consists of a layer containing a light-emitting material (EL layer) sandwiched between a pair of electrodes. By applying a voltage between the electrodes of this device, light emission is obtained from the light-emitting material. Since the aforementioned light-emitting element is self-illuminating, display devices using it have advantages such as excellent visibility, no need for a backlight, and low power consumption. Furthermore, they can be manufactured to be thin and lightweight, and have advantages such as high response speed. In the case of a light-emitting element (for example, an organic EL element) that uses an organic compound as the light-emitting material and has an EL layer containing the light-emitting material between a pair of electrodes, applying a voltage between the pair of electrodes causes electrons to be injected from the cathode and holes from the anode into the light-emitting EL layer, causing an electric current to flow. The injected electrons and holes then recombine, causing the light-emitting organic compound to enter an excited state, and light emission can be obtained from the excited light-emitting organic compound. Organic compounds can form two types of excited states: singlet excited states (S * ) and triplet excited states (T * ). Emission from the singlet excited state is called fluorescence, and emission from the triplet excited state is called phosphorescence. The statistical generation ratio of these states in light-emitting devices is S * : T * = The ratio is 1:3. Therefore, compared to a light-emitting element using a fluorescent compound, Light-emitting devices using phosphorescent compounds (phosphorescent compounds) can achieve higher luminescence efficiency. Therefore, the development of light-emitting devices using phosphorescent compounds that can convert triplet excited states into light emission has been actively pursued in recent years. Among light-emitting devices using phosphorescent compounds, in particular, light-emitting devices that emit blue light, Because it is difficult to develop stable compounds with high triplet excitation energy levels, practical applications have not yet been achieved. Therefore, efforts are being made to develop light-emitting devices using more stable fluorescent compounds, and methods are being explored to improve the luminescence efficiency of light-emitting devices using fluorescent compounds (fluorescent light-emitting devices). As a material capable of converting a portion of the triplet excited state into light emission, thermally activated delayed fluorescence ( Thermally Activated Delayed Fluorescence A TADF (Turbine-Adjusted-Focused) form is known. In thermally activated delayed phosphors, a singlet excited state is generated from a triplet excited state by reverse intersystem crossing, and this singlet excited state is converted into luminescence. In light-emitting devices using thermally activated delayed phosphors, increasing luminescence efficiency requires not only efficient generation of singlet excited states from triplet excited states in the thermally activated delayed phosphor, but also efficient emission from the singlet excited state, i.e., a high fluorescence quantum yield. However, designing a light-emitting material that satisfies both of these conditions simultaneously is difficult. Therefore, in a light-emitting device having a thermally activated delayed phosphor and a fluorescent compound, a method has been proposed in which the singlet excitation energy of the thermally activated delayed phosphor is transferred to the fluorescent compound, and light emission is obtained from the fluorescent compound (see Patent Document 1). Japanese Patent Publication No. 2014-45179 A schematic cross-sectional view of a light-emitting element according to one embodiment of the present invention, and a diagram illustrating the correlation of energy levels in the light-emit