Delayed Fluorescence Compound for OLED Efficiency
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Solution Overview
Problem
Current OLEDs using fluorescent compounds have limited emitting efficiency, particularly for blue phosphorescent compounds, which fail to meet requirements in terms of efficiency and reliability, with maximum emitting efficiency being less than approximately 5% due to the exclusion of triplet excitons from emission.
Innovation Solution
A delayed fluorescence compound incorporating an electron acceptor moiety of benzo[4,5]thieno[2,3-b]quinoxaline combined with an electron donor moiety, such as carbazole or acridine, is used in the OLED structure, allowing both singlet and triplet excitons to participate in emission, thereby enhancing efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If fluorescent compound is used as emitting material, then device structure is simple, but emitting efficiency is limited to less than 5% due to exclusion of triplet excitons
Solution Approach 1:
The patent employs a composite emitting layer containing both fluorescent compound and phosphorescent compound. The fluorescent compound provides structural simplicity and fast response, while the phosphorescent compound enables triplet exciton utilization. This composite approach achieves internal quantum efficiency exceeding 25% by combining the advantages of both material types without requiring complete structural redesign.
Solution Approach 2:
The patent modifies the emitting material composition by introducing phosphorescent compounds with specific triplet energy levels and phosphorescence quantum efficiencies. By adjusting the ratio of fluorescent to phosphorescent compounds and selecting materials with appropriate energy level alignments, the system achieves high emitting efficiency while maintaining operational simplicity.
2Productivity
If phosphorescent compound is used to engage triplet excitons in emission, then emitting efficiency improves, but reliability and color stability deteriorate, especially for blue emission
Solution Approach 1:
The patent uses a composite system where fluorescent and phosphorescent compounds work synergistically. The fluorescent component provides stable, reliable emission characteristics, while the phosphorescent component contributes triplet exciton utilization. This combination mitigates the color instability and reliability issues of pure phosphorescent materials, particularly for blue emission, by distributing the emission burden across both material types.
Solution Approach 2:
The patent optimizes the local properties of the emitting layer by carefully selecting phosphorescent compounds with specific triplet energy levels that are higher than the fluorescent compound's S1 energy. This energy level alignment ensures that triplet excitons are efficiently transferred to the phosphorescent compound only when appropriate, maintaining color stability while improving efficiency. The localized energy transfer mechanism prevents the color instability that plagues pure phosphorescent systems.
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 use of the delayed fluorescence compound significantly improves the emitting efficiency of OLEDs, potentially achieving theoretical quantum efficiency of 100% by engaging both singlet and triplet excitons in the emission process, while also enhancing color purity and reducing the red shift issue.
Implementation Method 1
allowing both singlet and triplet excitons to participate in emission
Implementation Method 2
engaging both singlet and triplet excitons in the emission process
Implementation Method 3
when an electron from a cathode, which serves as an electron-injecting electrode, and a hole from an anode, which serves as a hole-injecting electrode, are injected into an emitting material layer, the electron and the hole are combined and become extinct such that the light is emitted from the OLED
Data Source
AI summary
Embodiments relate to a delayed fluorescence compound and a display device including the delayed fluorescence compound. The delayed fluorescence compound includes an electron acceptor moiety of benzo[4,5]thieno[2,3-b]quinoxaline and at least one electron donor moiety covalently bonded to the electron acceptor moiety. The at least one electron donor moiety is covalently bonded to a benzene ring of benzo[4,5]thieno[2,3-b]quinoxaline and is selected from carbazole, phenylcarbazole, acridine, and phenylacridine. The effective charge transfer in the delayed fluorescence compound results in improved emitting efficiency of the compound.