OLED Light-Emitting Layer Structure for Higher TTA Fluorescence
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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 through triplet-triplet annihilation (TTA), which limits the proportion of delayed fluorescence components and overall emission efficiency, especially for blue light emission.
Innovation Solution
A light-emitting element structure is designed with a host material 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 via TTA, with a guest fluorescent material having a higher triplet excitation energy, increasing the delayed fluorescence component to at least 10% of total emission.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a fluorescent material is used in a light-emitting element, then the device structure is simpler compared to phosphorescent materials, but the emission efficiency is lower due to limited triplet exciton conversion
Solution Approach 1:
The patent introduces a host material as an intermediary between the fluorescent guest material and triplet excitons. The host material with deep triplet energy level acts as a mediator to facilitate triplet-triplet annihilation, enabling efficient conversion of triplet excitons to singlet excitons that can emit light through the fluorescent guest material, thus improving emission efficiency while maintaining device structural simplicity
Solution Approach 2:
The patent changes the energy level parameters of the host material, specifically selecting materials with deep triplet energy levels (higher than the guest material's triplet energy). This parameter change enables effective triplet exciton confinement and facilitates TTA process, converting non-emissive triplet excitons into emissive singlet excitons, thereby improving the proportion of delayed fluorescence and overall emission efficiency
2Use of energy by moving object
If the proportion of delayed fluorescence component is increased through TTA, then emission efficiency improves, but the device complexity increases due to additional material requirements
Solution Approach 1:
The patent applies local quality by creating a specific light-emitting layer composition where a fluorescent guest material is dispersed in a host material with specific properties (deep triplet energy level). This localized functional design ensures that TTA occurs primarily in this layer, increasing delayed fluorescence proportion without requiring complex modifications throughout the entire device structure
Solution Approach 2:
The patent uses composite materials by combining a fluorescent guest material with a host material having deep triplet energy level. This composite light-emitting layer leverages the advantages of both materials: the fluorescent guest provides simple device structure while the host material enables efficient triplet exciton conversion through TTA, achieving high emission efficiency without excessive complexity
3Illumination intensity
If triplet-triplet annihilation is enhanced to convert more triplet excitons, then light output increases, but power consumption management becomes more complex
Solution Approach 1:
The patent implements self-service by designing a system where triplet excitons automatically undergo TTA conversion through the host material's energy level structure. The deep triplet energy level of the host material creates a natural energy funnel that guides triplet exciton conversion to singlet excitons without requiring external control mechanisms, increasing light output while avoiding complex power management systems
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
This configuration significantly improves the emission efficiency of the light-emitting element by increasing the proportion of delayed fluorescence, leading to higher light output with reduced power consumption and enhanced blue light emission performance.
Implementation Method 1
As an emission mechanism capable of converting part of a triplet excited state into light emission, 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
In a basic structure of such a light-emitting element, a layer containing a light-emitting material (an EL layer) is interposed between a pair of electrodes. 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.