OLED Anthracene Derivative TTA Delayed Fluorescence
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Solution Overview
Problem
Conventional organic light-emitting diodes face limitations in luminous efficiency due to the low internal quantum efficiency of fluorescent EL devices, which is restricted by the 25% theoretical limit for singlet exciton formation, and the scarcity of compounds that effectively utilize the triplet-triplet annihilation (TTA) phenomenon for enhanced efficiency.
Innovation Solution
Incorporating an anthracene derivative with a specific structure into the light-emitting layer, where the second triplet excited orbital energy level is higher than twice the lowest triplet excited orbital energy level, to facilitate the TTA phenomenon and promote delayed fluorescence, thereby improving luminous efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a single material is employed as the luminescent material, then the device structure is simple, but intermolecular actions cause the maximum luminescence wavelength to shift toward a longer wavelength, resulting in a reduction in color purity and luminous efficiency
Solution Approach 1:
The patent employs a host-dopant system where a dopant material is added to the light-emitting layer. The dopant has a smaller energy band gap than the host, enabling energy transfer from the host to the dopant. This composite material approach allows the host to provide structural stability while the dopant determines the emission wavelength, thereby maintaining color purity and luminous efficiency without requiring a complex multi-layer device structure.
2Ease of operation
If fluorescent EL devices are used, then the device operation is straightforward, but only the formation of singlet excitons results in the emission of useful radiation, placing a theoretical limit of 25% on the internal quantum efficiency
Solution Approach 1:
The patent changes the energy level parameters of the dopant material, specifically selecting a dopant with a smaller energy band gap than the host material. This parameter change enables the dopant to accept energy from the host through radiative energy transfer, allowing triplet excitons to be converted into singlet excitons that can emit light. This approach maintains straightforward device operation while overcoming the 25% internal quantum efficiency limit by utilizing both singlet and triplet excitons for light emission.
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 introduction of the anthracene derivative with a specific structure in the light-emitting layer enhances luminous efficiency by leveraging the TTA phenomenon, achieving a higher internal quantum efficiency compared to conventional organic light-emitting diodes.
Implementation Method 1
a method for fabricating an organic light-emitting diode of high efficiency has been proposed in which advantage of taken of the effective occurrence of a triplet-triplet fusion (TTF) or triplet-triplet annihilation (TTA) phenomenon accounting for the generation of singlet excitons through the collision and fusion of two triplet excitons
Implementation Method 2
to facilitate the TTA phenomenon and promote delayed fluorescence, thereby improving luminous efficiency
Implementation Method 3
In the luminescent zone, the carriers such as holes and electrons recombine to produce an exciton. When the exciton returns to the ground state from the excited state, the molecule of the light-emitting layer emits light
Data Source
AI summary
Disclosed herein is an organic light emitting diode, comprising: a first electrode; a second electrode facing the first electrode; and a light emitting layer interposed between the first electrode and the second electrode, wherein the light-emitting layer contains at least one of the anthracene derivatives represented by the following Chemical Formula A and having an orbital energy level of TTA phenomenon-based singlet generation in which the second triplet excited orbital energy level (T2) is higher than two times the lowest triplet excited orbital energy level (T1) (T2>2T1).