OLED Layered Emission Structure for Efficient Delayed Fluorescence
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Solution Overview
Problem
Existing organic light-emitting devices with a single light-emitting layer composed of a thermally-activating delayed fluorescent material and a host material exhibit low efficiency and short driving lifetime, necessitating further improvements.
Innovation Solution
A layered configuration is employed, where an exciton generation layer containing a compound with a small ΔE ST difference between the lowest excited singlet and triplet energy levels is positioned on one or both sides of a light-emitting layer, separated by isolation layers, to enhance energy transfer and emission efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a single light emitting layer is used with thermally-activating delayed fluorescent material and host material, then the device structure is simple, but the emission efficiency is low and driving lifetime is short
Solution Approach 1:
The light emitting device is divided into multiple functional layers: a first light emitting layer containing thermally-activating delayed fluorescent material, a second light emitting layer containing fluorescent material, and a spacer layer interposed between them. This segmentation allows each layer to perform its specific function optimally, improving overall emission efficiency and device lifetime while maintaining reasonable structural complexity.
2Productivity
If triplet excitons are generated in ordinary fluorescent light emitting material, then they have high generation efficiency, but they lose energy through thermal radiation and cannot contribute to emission
Solution Approach 1:
The patent introduces a thermally-activating delayed fluorescent material as an intermediary substance in the first light emitting layer. This material acts as a mediator that facilitates the conversion of triplet excitons to singlet excitons through reverse intersystem crossing, enabling triplet excitons to indirectly contribute to fluorescence emission and reducing energy loss through thermal radiation.
Solution Approach 2:
The patent changes the energy level parameters of the light emitting layers by selecting materials with specific triplet and singlet energy levels. The thermally-activating delayed fluorescent material is chosen to have appropriate energy level differences that enable efficient reverse intersystem crossing at operating temperatures, thereby converting non-emissive triplet excitons into emissive singlet excitons.
3Reliability
If a layered configuration with exciton generation layer and isolation layers is used, then energy transfer and emission efficiency are enhanced, but the device structure becomes more complex
Solution Approach 1:
The device is segmented into functionally distinct layers: an exciton generation layer for generating excitons, isolation layers for separating and managing exciton populations, and light emitting layers for light emission. This segmentation improves energy transfer efficiency by optimizing each layer's function while maintaining a manageable structural complexity through clear functional division.
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 results in a high-efficiency organic light-emitting device with a significantly extended lifetime, driven at low voltage and offering narrow emission peaks with excellent chromaticity and color purity.
Implementation Method 1
the thermally-activating delayed fluorescent material is a compound that undergoes reverse intersystem crossing from an excited triplet state to an excited singlet state through absorption of heat energy
Implementation Method 2
observation of fluorescence radiation from the singlet excitons directly excited from a ground singlet state therein is followed by delayed observation of fluorescence radiation from the singlet excitons formed through reverse intersystem crossing therein (delayed fluorescence radiation)
Implementation Method 3
an exciton generation layer containing a compound with a small ΔE ST difference between the lowest excited singlet and triplet energy levels is positioned on one or both sides of a light-emitting layer, separated by isolation layers, to enhance energy transfer and emission efficiency
Implementation Method 4
the singlet excitons among them emit fluorescence through radiative deactivation to be in a ground singlet state
Data Source
Figure 1~2
AI summary
An organic light emitting device having an exciton generation layer that contains a compound having a difference between the lowest excited singlet energy level ES1 and the lowest excited triplet energy level ET1 thereof of 0.3 eV or less, or an exciplex to emit delayed fluorescence, and a light emitting layer that contains a light emitting material has a high efficiency and a long lifetime.