Luminescent Material for Delayed Fluorescence in OLED Devices
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Solution Overview
Problem
Current organic electroluminescent devices face limitations in achieving high luminous efficiency, long lifespan, and low driving voltage due to the inefficiencies of existing fluorescent and phosphorescent dopants, with recent compounds for delayed fluorescence still exhibiting low luminous efficiency and high energy differences between singlet and triplet exciton states.
Innovation Solution
A luminescent material represented by a specific compound formula, which enables thermally activated delayed fluorescence by optimizing the energy difference between singlet and triplet exciton states, thereby enhancing internal quantum efficiency and luminous efficiency, is used in the organic electroluminescent device.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a fluorescent dopant is used, then the device structure is simple, but the internal quantum efficiency is limited to 25%
Solution Approach 1:
The invention changes the energy parameter ΔEST between singlet and triplet exciton states to be very small (lower than 0.2 eV), enabling thermally activated delayed fluorescence. This parameter change allows triplet excitons to convert to singlet excitons and emit light, achieving internal quantum efficiency exceeding 25% while maintaining a relatively simple device structure without requiring heavy metal complexes.
2Use of energy by moving object
If a phosphorescent dopant based on metal complex is used, then the internal quantum efficiency can reach 100%, but the material cost is high and reserves are limited
Solution Approach 1:
The invention replaces expensive and limited metal complex materials (such as Ir) with organic luminescent compounds that can achieve high internal quantum efficiency through delayed fluorescence mechanism. These organic compounds are more abundant and cost-effective, providing a sustainable alternative to rare metal-based phosphorescent dopants.
3Illumination intensity
If compounds with high ΔEST are used for delayed fluorescence, then the fluorescent mechanism works well, but the triplet exciton cannot efficiently convert to singlet exciton, resulting in low luminous efficiency
Solution Approach 1:
The invention optimizes the energy difference parameter ΔEST between singlet and triplet exciton states to be very small (lower than 0.2 eV). This parameter optimization enables efficient thermal activation of triplet excitons to singlet excitons through reverse intersystem crossing, while maintaining strong fluorescence emission. The balanced design achieves both high fluorescence intensity and high luminous efficiency simultaneously.
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 luminescent material significantly improves the luminous efficiency, extends the lifespan, and reduces the driving voltage of organic electroluminescent devices, achieving high current efficiency and excellent color purity.
Implementation Method 1
the E-type delayed fluorescence is activated by heat energy, it is known as thermally activated delayed fluorescence
Implementation Method 2
the triplet exciton emits light by reverse-intersystem crossing to a singlet exciton, i.e. delayed fluorescence
Implementation Method 3
Holes and electrons are recombined at a light-emitting layer to form an exciton of high energy. Due to the energy of the exciton, the organic luminescent material transfers to an excited state, and emits light when it returns to a ground state.
Data Source
AI summary
The present invention relates to a luminescent material for delayed fluorescence and an organic electroluminescent device comprising the same. By using the luminescent material for delayed fluorescence according to the present invention, an organic electroluminescent device having long lifespan, low driving voltage, excellent color purity, and significantly improved luminous efficiency such as current efficiency is provided.