Organic EL Device TADF Host Triplet Mediator
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Solution Overview
Problem
Current organic electroluminescence devices have limitations in luminous efficiency and lifetime, with existing technologies struggling to effectively utilize triplet excitons for improved performance.
Innovation Solution
Incorporating specific compounds represented by formulas (1) and (3) in the organic electroluminescence device structure, where the first organic layer includes a fluorescent compound and a delayed fluorescent compound, and the second organic layer features a compound with a specific Cz-aryl skeleton, enhancing carrier balance and efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a fluorescent organic EL device uses only singlet excitons for emission, then the device structure is simple, but the internal quantum efficiency is limited to maximum 25%
Solution Approach 1:
The patent introduces a TADF host material with specific energy level parameters (small singlet-triplet energy gap ΔEST) to enable thermal activation of triplet excitons. By changing the energy level parameters of the host material, triplet excitons can be converted to singlet excitons through reverse intersystem crossing, allowing both singlet and triplet excitons to contribute to emission and achieving internal quantum efficiency exceeding 25%.
2Loss of energy
If triplet excitons are utilized through TADF mechanism, then luminous efficiency is improved, but device lifetime is reduced due to triplet exciton accumulation
Solution Approach 1:
The patent introduces a triplet exciton mediator material in the triplet exciton removal layer that has a triplet energy level higher than the TADF host but lower than the fluorescent guest. This mediator acts as an intermediary to accept triplet excitons from the TADF host through triplet-triplet energy transfer, preventing triplet exciton accumulation in the emitting layer while enabling efficient energy transfer to extend device lifetime without sacrificing luminous efficiency.
3Loss of energy
If carrier balance is improved by adjusting layer composition, then luminous efficiency increases, but device complexity increases
Solution Approach 1:
The patent segments the organic light-emitting layer into three distinct functional layers: a TADF host layer for generating excitons, a triplet exciton removal layer with mediator material for managing triplet excitons, and a fluorescent guest layer for light emission. This segmentation allows each layer to be optimized for its specific function, improving carrier balance and luminous efficiency while maintaining clear functional boundaries that simplify device design and fabrication.
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 improves at least one of luminous efficiency and lifetime by reducing hole supply to the emitting layer, resulting in a high-performance organic electroluminescence device.
Implementation Method 1
a thermally activated delayed fluorescence (TADF) mechanism has been studied. The TADF mechanism uses a phenomenon where inverse intersystem crossing from triplet excitons to singlet excitons thermally occurs when a material having a small energy difference (ΔST) between singlet energy level and triplet energy level is used.
Implementation Method 2
When a voltage is applied to an organic electroluminescence device (hereinafter, occasionally referred to as 'organic EL device'), holes and electrons are injected into an emitting layer from an anode and a cathode, respectively. The injected electrons and holes are recombined in the emitting layer to form excitons.
Implementation Method 3
the second organic layer includes a third compound... the third compound is a compound represented by a formula (3) below... enhancing carrier balance and efficiency
Data Source
AI summary
An organic electroluminescence device includes an anode, a second organic layer, a first organic layer, and a cathode in this order. The first organic layer contains a first compound and a second compound. The second organic layer contains a third compound. The first compound is a compound represented by a formula (1). The second compound is a delayed fluorescent compound. The third compound is a compound represented by a formula (3). In the formula (1), X is a nitrogen atom or a carbon atom bonded to Y, Y being a hydrogen atom or a substituent. In the formula (3), n is an integer ranging from 1 to 4, XB is a group represented by a formula (3A). In the formula (3A), Ar1 and Ar2 are each independently a monovalent or polyvalent aromatic hydrocarbon group, and Cz is a group represented by a formula (3B-1) or the like.