Organic Electroluminescence Element Delayed Fluorescent Exciplex Layer
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Solution Overview
Problem
The quantum yield of phosphorescence in organic electroluminescent devices is lower than fluorescence due to the longer lifetime of triplet excitons, leading to saturation and energy deactivation, which limits the overall light emission efficiency despite using both singlet and triplet excitons for emission.
Innovation Solution
Incorporating a delayed fluorescent exciplex layer between the light emitting layer and the electrode, composed of a donor and acceptor compound, with a triplet exciton blocking layer to suppress triplet excitation energy transfer, ensuring efficient singlet excited state formation and emission through the Foerster mechanism.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If a phosphorescent light emitting layer is used to utilize triplet excitons for light emission, then the light emission efficiency is improved compared to using only singlet excitons, but the quantum yield of phosphorescence becomes lower than fluorescence due to the longer lifetime of triplet excitons causing saturation and energy deactivation
Solution Approach 1:
The device is divided into distinct functional layers: a fluorescent light emitting layer for high quantum yield emission and a phosphorescent light emitting layer for triplet exciton utilization. This segmentation allows each layer to operate in its optimal regime without the drawbacks of the other, resolving the contradiction between overall efficiency and quantum yield.
Solution Approach 2:
An exciton forming layer is introduced as an intermediary between the fluorescent and phosphorescent light emitting layers. This layer facilitates controlled energy transfer and exciton generation, enabling the system to achieve both high quantum yield in the fluorescent layer and efficient triplet exciton utilization in the phosphorescent layer, thereby resolving the quantum yield limitation.
2Productivity
If both fluorescent and phosphorescent light emitting layers are combined to utilize singlet and triplet excitons, then the overall light emission efficiency is enhanced, but the device complexity increases
Solution Approach 1:
The exciton forming layer serves multiple functions: it generates excitons through carrier recombination, transfers energy to both fluorescent and phosphorescent layers, and controls the distribution of singlet and triplet excitons. This multi-functionality reduces the need for additional complex components while achieving efficient utilization of both exciton types.
Solution Approach 2:
The device utilizes changes in energy transfer parameters and exciton distribution to optimize performance. By controlling the energy levels and transfer mechanisms between layers, the system achieves high efficiency without requiring complex structural modifications, resolving the contradiction between efficiency enhancement and device 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 configuration enhances light emission efficiency by promoting the formation of singlet excitons and preventing triplet exciton deactivation, resulting in improved quantum yield and emission efficiency.
Implementation Method 1
the singlet excitation energy is transferred to the light emitting material of the light emitting layer through the Foerster mechanism, whereby the light emitting material efficiently emits fluorescent light
Implementation Method 2
in the excited state, inverse intersystem crossing from the triplet excited state to the singlet excited state occurs in the layer
Data Source
Figure 1(a)~1(c)
Figure 2~3
Figure 4~5
AI summary
An organic electroluminescent device comprising at least two organic layers including a light emitting layer (5) and a delayed fluorescent exciplex layer (7) containing a donor compound and an acceptor compound, between a pair of electrodes (2, 9) is highly efficient in formation of a singlet excited state and enables high light emission efficiency.