OLED Emitting Layer Using TADF-Phosphorescent Energy Transfer
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Solution Overview
Problem
Organic electroluminescence (EL) elements face limitations in external quantum efficiency and drive voltage, particularly when using phosphorescent compounds, with light extraction efficiency ranging from 20% to 30% and a maximum external quantum efficiency of 25% due to factors like concentration quenching and triplet-triplet annihilation.
Innovation Solution
Incorporating a thermally activated delayed fluorescence (TADF) material in the light-emitting layer, where the fluorescence spectrum of the TADF material overlaps with the absorption spectrum of the phosphorescent compound, enhancing energy transfer efficiency and reducing drive voltage by ensuring efficient energy transfer and emission.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If a phosphorescent compound is used in the light-emitting layer, then internal quantum efficiency can be increased to 100%, but external quantum efficiency is limited to approximately 25% due to light extraction efficiency of 20-30%
Solution Approach 1:
The patent introduces a fluorescent compound as an intermediary material between the electrodes and the phosphorescent compound. This fluorescent compound absorbs energy from the phosphorescent compound and re-emits it as light, facilitating more efficient light extraction from the device. The intermediary fluorescent compound acts as a bridge to overcome the light extraction bottleneck, enabling higher external quantum efficiency while maintaining the high internal quantum efficiency provided by the phosphorescent compound.
2Productivity
If the phosphorescent compound is dispersed in a host material matrix to suppress concentration quenching, then emission efficiency is maintained, but device complexity increases
Solution Approach 1:
The patent combines the phosphorescent compound and fluorescent compound into a single integrated light-emitting layer rather than using separate layers. This merging approach maintains the emission efficiency benefits of the phosphorescent compound dispersed in a host matrix while simplifying the overall device structure. The two compounds work synergistically within the same layer, reducing manufacturing complexity and improving device reliability.
3Device complexity
If conventional fluorescent compounds are used, then the structure is simple, but internal quantum efficiency is limited to 25% due to singlet-triplet state ratio
Solution Approach 1:
The patent creates a composite light-emitting layer containing both phosphorescent and fluorescent compounds working together. The phosphorescent compound provides access to triplet states for high internal quantum efficiency, while the fluorescent compound facilitates light extraction. This composite material approach achieves superior performance by combining the advantages of both material types, overcoming the 25% efficiency limitation of conventional fluorescent compounds without significantly increasing structural complexity.
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 increases external quantum efficiency and reduces drive voltage, leading to higher emission efficiency and longer lifetimes while maintaining high power efficiency, effectively addressing the limitations of existing organic EL elements.
Implementation Method 1
a peak of a fluorescence spectrum of the material exhibiting thermally activated delayed fluorescence overlaps with a lowest-energy-side absorption band in an absorption spectrum of the phosphorescent compound
Implementation Method 2
the phosphorescent compound exhibits phosphorescence in the light-emitting layer by voltage application between the pair of electrodes
Implementation Method 3
a light-emitting layer which contains a phosphorescent compound and a material exhibiting thermally activated delayed fluorescence
Data Source
AI summary
Provided is a light-emitting element with high external quantum efficiency and a low drive voltage. The light-emitting element includes a light-emitting layer which contains a phosphorescent compound and a material exhibiting thermally activated delayed fluorescence between a pair of electrodes, wherein a peak of a fluorescence spectrum and/or a peak of a phosphorescence spectrum of the material exhibiting thermally activated delayed fluorescence overlap(s) with a lowest-energy-side absorption band in an absorption spectrum of the phosphorescent compound, and wherein the phosphorescent compound exhibits phosphorescence in the light-emitting layer by voltage application between the pair of electrodes.