Stacked Organic EL Device Reducing Current Density
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Solution Overview
Problem
Thermally activated sensitized fluorescence (TASF) devices face efficiency and service life decay issues due to high current density, which leads to efficiency roll-off and exciton diffusion in the light-emitting layer.
Innovation Solution
A stacked organic electroluminescent device structure is implemented, comprising multiple organic electroluminescent units with a TASF unit and a triplet-triplet annihilation (TTA) unit arranged in a stacked manner, reducing current density and optimizing energy levels to enhance efficiency and service life.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If a TASF unit is used to achieve complete energy transfer and exceed 25% internal quantum efficiency, then efficiency is improved, but current density becomes excessively high causing efficiency roll-off and exciton diffusion
Solution Approach 1:
The device is divided into multiple stacked organic electroluminescent units, where a first unit generates excitons and a second unit emits light through triplet-triplet annihilation. This segmentation allows the first unit to operate at lower current density while maintaining high efficiency, and the second unit to convert triplet excitons to singlet excitons for light emission, thereby resolving the contradiction between achieving high internal quantum efficiency and avoiding efficiency roll-off that reduces service life.
2Illumination intensity
If high current density is applied to achieve high luminance, then luminance is improved, but efficiency roll-off and exciton diffusion occur reducing service life
Solution Approach 1:
The first organic electroluminescent unit acts as an intermediary that generates triplet excitons at lower current density, which are then transferred to the second unit for light emission. This intermediary mechanism allows the device to achieve high luminance without subjecting the light-emitting layer to excessive current density, thereby preventing efficiency roll-off and exciton diffusion that would otherwise reduce service life.
3Device complexity
If a single-layer TASF device structure is used to simplify device complexity, then manufacturing is easier, but efficiency and service life decay problems occur
Solution Approach 1:
The device is divided into multiple stacked organic electroluminescent units, where a first unit generates excitons and a second unit emits light through triplet-triplet annihilation. This segmentation allows the first unit to operate at lower current density while maintaining high efficiency, and the second unit to convert triplet excitons to singlet excitons for light emission, thereby resolving the contradiction between achieving high internal quantum efficiency and avoiding efficiency roll-off that reduces service life.
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 stacked device structure significantly reduces current density under the same luminance, thereby improving efficiency and extending the service life by preventing efficiency roll-off and exciton diffusion.
Implementation Method 1
the triplet energy of the host material is returned to the singlet state through a reverse intersystem crossing (RISC) process, thereby transferring the energy to a doped fluorescent dye to emit light
Implementation Method 2
when a thermally activated delayed fluorescence (TADF) material is used as a sensitizer, the energy of a host material is transferred to the TADF material
Implementation Method 3
the energy of a host material is transferred to the TADF material... a complete energy transfer from the host to dye molecules can be achieved
Implementation Method 4
The second host material is a triplet-triplet annihilation (TTA) material
Data Source
AI summary
An organic electroluminescent device and a display apparatus. The organic electroluminescent device includes a first electrode, a second electrode and at least two organic electroluminescent units located between the first electrode and the second electrode. The at least two organic electroluminescent units are arranged in a stacked manner. The at least two organic electroluminescent units include a first organic electroluminescent unit. The first organic electroluminescent unit includes a first light-emitting layer. The first light-emitting layer contains a first host material, a thermally activated delayed fluorescence sensitizer and a first fluorescent dye.