Organic Electroluminescent Element TADF Dopant Efficiency
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Solution Overview
Problem
Current organic electroluminescence devices have limitations in achieving high luminous efficiency, particularly for fluorescent EL devices compared to phosphorescent devices, and there is a need for improved internal quantum efficiency beyond what is achieved with existing delayed fluorescence mechanisms.
Innovation Solution
An organic electroluminescence device incorporating a specific emitting layer with a dopant material represented by a particular formula, which includes a compound with a balanced electron donating and accepting moiety structure, facilitating thermally activated delayed fluorescence (TADF) to enhance luminous efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a fluorescent EL device uses emission caused by singlet excitons, then the device structure is simpler and lifetime is extended, but the internal quantum efficiency is limited to 25% at maximum
Solution Approach 1:
The patent changes the energy level parameters of the emitting layer materials, specifically using a host material with triplet energy level (T1) of 2.5-3.5 eV and a dopant material with singlet energy level (S1) of 2.7-3.7 eV and triplet energy level (T1) of 2.4-3.4 eV. This parameter optimization enables efficient TADF while maintaining fluorescent device simplicity and lifetime.
Solution Approach 2:
The patent introduces a dopant material as an intermediary substance with specific energy level characteristics that facilitates the TADF mechanism. The dopant acts as a mediator to enable efficient reverse intersystem crossing from triplet to singlet state, achieving high internal quantum efficiency while maintaining the advantages of fluorescent devices.
2Use of energy by moving object
If a phosphorescent EL device uses emission caused by triplet excitons, then the internal quantum efficiency can be improved up to 100%, but the device complexity increases and lifetime is reduced
Solution Approach 1:
The patent inverts the conventional approach by using a fluorescent device structure with TADF mechanism instead of a phosphorescent device. The emitting layer is designed to emit delayed fluorescence through reverse intersystem crossing, achieving high internal quantum efficiency without the drawbacks of phosphorescent devices such as heavy metal use, device complexity, and reduced lifetime.
3Use of energy by moving object
If a delayed fluorescence emitter with small energy difference between singlet and triplet levels is used, then the internal quantum efficiency can reach 100%, but the manufacturing precision requirements increase
Solution Approach 1:
The patent defines specific parameter ranges for host and dopant materials that balance manufacturing feasibility with high efficiency. The energy level parameters are optimized to ensure small ΔEST while maintaining manufacturability: host T1 (2.5-3.5 eV), dopant S1 (2.7-3.7 eV), and dopant T1 (2.4-3.4 eV).
Solution Approach 2:
The patent uses a composite emitting layer comprising both host material and dopant material with complementary energy level characteristics. This composite structure enables precise control of the TADF mechanism while simplifying manufacturing, as the host-guest system allows energy level tuning through material selection rather than complex synthesis control.
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 proposed device exhibits improved luminous efficiency through the TADF mechanism, potentially achieving internal quantum efficiency up to 100%, surpassing the limitations of previous delayed fluorescence technologies.
Implementation Method 1
a highly efficient fluorescent organic EL device using delayed fluorescence has been suggested and developed. For instance, an organic EL device using a triplet-triplet fusion (TTF) mechanism, which is one of mechanisms of delayed fluorescence, is suggested.
Implementation Method 2
The TADF mechanism uses such a phenomenon that inverse intersystem crossing from triplet excitons to singlet excitons occurs when a material having a small energy difference between singlet energy level and triplet energy level is used.
Implementation Method 3
When such a compound having a small ΔST is used, inverse intersystem crossing from a triplet energy level to a singlet energy level is caused by a heat energy.
Data Source
AI summary
An organic electroluminescence device includes: an anode; a cathode; and a single- or multi-layer organic layer interposed between the anode and the cathode. The organic layer includes at least one emitting layer containing a dopant material represented by a formula below. In the formula, X1 to X5 each independently represent CR1 or a nitrogen atom, at least one of X1 to X5 is a nitrogen atom, L1 represents a divalent aromatic hydrocarbon group or a divalent heterocyclic group, A and B each independently represents a cyclic structure, at least one of the cyclic structure A and the cyclic structure B has a substituent, and R1 represents an aryl group, alkyl group or the like.