Fluorescent EL Layer Structure for Triplet-Triplet Annihilation
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Solution Overview
Problem
Current light-emitting elements using fluorescent materials face challenges in achieving high emission efficiency, particularly in converting triplet excitons into singlet excitons for enhanced light emission, especially for blue light emission where stable materials with high triplet excitation energy are difficult to develop.
Innovation Solution
A light-emitting element structure is designed with a host material in the light-emitting layer that has a lower triplet excitation energy level than the guest material, facilitating triplet-triplet annihilation (TTA) to increase the proportion of delayed fluorescence, thereby improving emission efficiency. This structure includes an anode, a cathode, and an electroluminescent layer with a light-emitting layer and an electron-transport layer, where the LUMO level of the electron-transport material is lower than the host material, enhancing the conversion of triplet excitons to singlet excitons.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a fluorescent material is used in a light-emitting element, then the device structure is simpler and stability is improved, but emission efficiency is reduced due to inability to convert triplet excitons into light
Solution Approach 1:
The patent introduces a host material as an intermediary substance with triplet excitation energy lower than the guest fluorescent material. This host material mediates the conversion of triplet excitons from the guest material into singlet excitons through triplet-triplet annihilation, enabling fluorescent materials to achieve high emission efficiency by utilizing triplet excitons that would otherwise be lost.
Solution Approach 2:
The patent changes the energy level parameters of the system by selecting a host material with specific triplet excitation energy lower than the guest material. This parameter change enables the thermodynamic feasibility of triplet-triplet annihilation, allowing efficient conversion of triplet excitons to singlet excitons while maintaining fluorescent material stability.
2Use of energy by moving object
If the triplet excitation energy level of the host material is higher than the guest material, then energy transfer is prevented, but triplet-triplet annihilation cannot occur to improve emission efficiency
Solution Approach 1:
The patent inverts the conventional energy level arrangement by selecting a host material with triplet excitation energy lower than the guest fluorescent material. This parameter inversion enables endothermic energy transfer from guest to host, creating the necessary conditions for triplet-triplet annihilation to occur efficiently in the host material.
Solution Approach 2:
The patent converts the previously harmful loss of triplet excitons (which cannot emit light in fluorescent materials) into a beneficial process by enabling triplet-triplet annihilation. The host material captures triplet excitons from the guest material and converts them into singlet excitons that can emit light, transforming energy loss into useful light emission.
3Ease of manufacture
If conventional fluorescent materials are used without TTA mechanism, then material development is easier, but emission efficiency remains low due to 75% triplet exciton loss
Solution Approach 1:
The patent introduces a host material as a mediator that facilitates triplet-triplet annihilation. This host material serves as an intermediate platform where triplet excitons from the fluorescent guest material can be converted into singlet excitons, enabling efficient light emission while maintaining the ease of using fluorescent materials.
Solution Approach 2:
The patent creates a composite light-emitting system combining a fluorescent guest material with a host material having lower triplet excitation energy. This composite structure leverages the stability and ease of fabrication of fluorescent materials while adding the TTA capability of the host material to achieve high emission efficiency.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The proposed structure significantly increases the proportion of delayed fluorescence due to TTA, leading to higher emission efficiency and lower power consumption, effectively addressing the limitations of existing technologies in achieving high emission efficiency, especially for blue light emission.
Implementation Method 1
triplet-triplet annihilation (TTA) is known. The TTA refers to a process in which, when two triplet excitons approach each other, excitation energy is transferred and spin angular momentum is exchanged to form a singlet exciton.
Implementation Method 2
light-emitting elements using electroluminescence (EL) have been actively researched and developed. By applying a voltage between the pair of electrodes of this element, light emission from the light-emitting material can be obtained.
Implementation Method 3
Light emission from the singlet excited state is referred to as fluorescence
Data Source
AI summary
A light-emitting element that includes a fluorescent material and has a high emission efficiency is provided. A light-emitting element in which a delayed fluorescence component due to TTA accounts for a high proportion of emissive components is provided. A novel light-emitting device with a high emission efficiency and a low power consumption is provided. A light-emitting element includes an anode, a cathode, and an EL layer. The EL layer includes a light-emitting layer including a host material and an electron-transport layer including a first material in contact with the light-emitting layer. The LUMO level of the first material is lower than that of the host material. The proportion of a delayed fluorescence component due to TTA is greater than or equal to 10 percent of the light emission from the EL layer. The proportion of the delayed fluorescence component due to TTA may be greater than or equal to 15 percent of the light emission.