OLED Mixed Emitters for Triplet Harvesting and Light Outcoupling
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Conventional organic light emitting devices (OLEDs) face inefficiencies due to the wastage of excitons, as only 25% are utilized for fluorescence, with the remaining 75% being trapped as triplet excitons, which are not efficiently emitted at room temperature, limiting their performance and stability.
Innovation Solution
Incorporating a phosphorescent/MADF emitter and a fluorescent emitter in the OLED structure, with energy transfer mechanisms like Dexter and Förster resonant energy transfer (FRET) to harness both singlet and triplet excitons, ensuring 100% utilization and enhancing efficiency and stability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If phosphorescent emitters are used to harvest triplet excitons, then exciton utilization efficiency improves, but device stability deteriorates
Solution Approach 1:
The patent introduces a fluorescent emitter as an intermediary between the phosphorescent emitter and the outside world. The phosphorescent emitter transfers energy to the fluorescent emitter, which then emits light. This mediator approach allows the system to benefit from efficient triplet exciton harvesting while avoiding the stability issues of blue phosphorescent materials, as the fluorescent emitter has longer operational stability.
2Productivity
If vertically oriented emitters are used in OLEDs, then internal quantum efficiency improves, but light outcoupling efficiency deteriorates
Solution Approach 1:
The patent employs horizontally oriented fluorescent emitters with asymmetric dipole orientation relative to the substrate. This asymmetric orientation (horizontal rather than vertical) creates favorable conditions for light extraction by reducing the overlap between the emission dipole and the substrate interface, thereby improving outcoupling efficiency while maintaining high internal quantum efficiency through effective exciton harvesting.
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 allows for 100% internal quantum efficiency by converting triplet excitons into fluorescent emission, significantly improving the external quantum efficiency and stability of OLEDs, particularly for blue phosphorescent OLEDs, while maintaining high outcoupling efficiency and color quality.
Implementation Method 1
energy transfer mechanisms like Dexter and Förster resonant energy transfer (FRET) to enhance exciton harvesting and emission efficiency
Implementation Method 2
energy transfer mechanisms like Dexter and Förster resonant energy transfer (FRET) to enhance exciton harvesting and emission efficiency
Implementation Method 3
emission from the triplet state can be facilitated through spin orbit coupling which incorporates a heavy metal atom in order to perturb the triplet state and add in some singlet character to and achieve a higher probability of radiative relaxation
Data Source
AI summary
Organic light emitting devices (OLEDs) with emissive layers containing both phosphorescent Pt complexes and fluorescent emitters, are described. The devices presented employ both fluorescent and phosphorescent Pt complexes in order to redistribute the excited states to primarily reside on known stable fluorescent emitters to achieve high device operational stability but maintain the high efficiency characteristic of phosphorescent OLEDs.