Thermally Activated Delayed Fluorescence Host for Phosphorescent OLED Efficiency
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Solution Overview
Problem
Conventional organic electroluminescence devices have limited external quantum efficiency due to the inability to utilize triplet state excitons efficiently, leading to high costs and device degradation, as they rely on expensive phosphorescence materials and suffer from roll-off issues under high luminance.
Innovation Solution
A thermally activated and sensitized phosphorescence organic electroluminescence device is developed, utilizing a luminescent layer with a host material composed of a hole transport material and an electron transport material, both being thermally activated delayed fluorescence materials, doped with a phosphorescent dye at a concentration less than 15wt%, which enables efficient energy transfer and reduces roll-off.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If phosphorescence materials are used to utilize triplet state excitons, then internal quantum efficiency reaches 100%, but the cost increases due to expensive rare heavy metals
Solution Approach 1:
The invention divides the luminescent layer into two distinct host materials (first host and second host) with different functions: the first host primarily utilizes triplet state excitons through TADF, while the second host facilitates energy transfer to the phosphorescence dopant. This segmentation allows efficient triplet state utilization without requiring high concentrations of expensive phosphorescence materials throughout the entire layer.
Solution Approach 2:
The invention applies different material properties to different regions/functions within the luminescent layer. The first host material is optimized for TADF with small singlet-triplet energy gap, while the second host material is optimized for energy transfer to phosphorescence. The phosphorescence dopant is concentrated in specific regions where it can effectively receive energy from the second host, reducing overall material cost while maintaining high efficiency.
2Use of energy by moving object
If high doping concentration of phosphorescence material is used, then energy transfer efficiency improves, but device life decreases and roll-off increases under high luminance
Solution Approach 1:
The invention segments the energy transfer pathway into two stages: first, the first host material converts triplet state excitons to singlet state excitons via TADF; second, the second host material transfers energy to the phosphorescence dopant. This segmentation allows the phosphorescence dopant to be used at lower concentrations (avoiding aggregation and degradation) while still achieving high energy transfer efficiency through the coordinated action of both hosts.
Solution Approach 2:
The second host material acts as an intermediary between the first host material and the phosphorescence dopant. It receives energy from the first host and efficiently transfers it to the phosphorescence dopant, enabling effective energy transfer at lower phosphorescence concentrations and reducing the harmful effects of high doping levels.
3Device complexity
If conventional fluorescence materials are used, then the device structure is simple, but external quantum efficiency is limited to below 5% due to inability to utilize triplet state excitons
Solution Approach 1:
The invention creates a composite luminescent layer system combining two host materials with complementary properties and a phosphorescence dopant. The first host material provides TADF capability to access triplet state excitons, while the second host material enables efficient energy transfer to phosphorescence. This composite approach maintains relative structural simplicity while achieving high external quantum efficiency through the synergistic interaction of the components.
Solution Approach 2:
The invention changes key energy parameters of the host materials: the first host is selected with a small singlet-triplet energy gap (ΔE_ST) to enable efficient TADF, while the second host is selected with appropriate triplet energy level to facilitate energy transfer to the phosphorescence dopant. These parameter optimizations allow the system to utilize triplet state excitons effectively without complex device structures.
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 approach enhances the utilization of triplet state excitons, improves luminescence efficiency, prolongs device life, and reduces the consumption of expensive phosphorescence materials, while maintaining low voltage and high efficiency.
Implementation Method 1
The energy gap between singlet state and triplet state (ΔE ST ) of this type of materials is very small, and the triplet state excitons, which cannot emit light, can be upconverted to singlet state excitons, which can emit light, under the effect of environmental heat.
Implementation Method 2
Because heavy atoms are introduced into phosphorescence materials, which results in spin-orbit coupling effect, the 75% of triplet state excitons can be sufficiently utilized, thereby achieving 100% of internal quantum efficiency.
Implementation Method 3
The thermally activated and sensitized luminescence mechanism utilizes a thermally activated delayed fluorescence material as the host and a phosphorescence material as the dye
Data Source
Figure 1~2
Figure 3~5
AI summary
The present invention discloses a thermally activated and sensitized phosphorescence organic electroluminescence device, comprising a luminescent layer, wherein a host material of the luminescent layer consists of two materials, wherein one of the two materials is a hole transport material, the other is an electron transport material, at least one of the two materials is a thermally activated delayed fluorescence material; and the host material is doped by a phosphorescent dye, and a proportion of the phosphorescent dye in the luminescent layer is <15wt%; and the triplet state energy level of the CT excited state of the thermally activated delayed fluorescence material is higher than the triplet state energy level of the n-π excited state by 0 to 0.3; or, the triplet state energy level of the CT excited state of the thermally activated delayed fluorescence material is higher than the triplet state energy level of the n-π excited state, wherein the difference is above 1.0eV, and, a difference between the second triplet state energy level of its n-π excited state and the first singlet state energy level of its CT excited state is-0.1 to 0.1eV.