Organic EL Element Host Material Design for Efficiency and Lifetime
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Solution Overview
Problem
Current organic electroluminescence (EL) elements face limitations in luminescent efficiency and stability, particularly in phosphorescent and delayed fluorescence types, which require improvements in internal quantum efficiency and lifetime while maintaining low driving voltage.
Innovation Solution
An organic EL element is designed with one or more light emitting layers containing a first host selected from compounds represented by general formula (1) and a second host from compounds represented by general formula (2), along with a luminescence dopant material, which can be a phosphorescence, fluorescence, or thermally activated delayed fluorescence dopant, to enhance efficiency and stability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If phosphorescent type organic EL element is used to increase internal quantum efficiency to 100%, then luminescent efficiency is improved, but lifetime is extended (worsened)
Solution Approach 1:
The patent changes the chemical structure parameters of host materials by introducing specific heterocyclic groups (triazine, pyrimidine, pyridine rings) and heteroatoms (N, O, S) to modify the energy levels and electronic properties of the light emitting layer, achieving both high efficiency and long lifetime
Solution Approach 2:
The patent uses composite host material systems combining multiple compounds with specific structural features (formulas 1-6) to create a synergistic effect that simultaneously achieves high luminescent efficiency and extended device lifetime, avoiding the trade-off present in single-material systems
2Productivity
If TADF mechanism is used to increase internal quantum efficiency to 100%, then luminescent efficiency is improved, but lifetime is extended (worsened)
Solution Approach 1:
The patent optimizes the energy gap between singlet and triplet states by selecting host materials with specific heterocyclic structures, enabling efficient reverse intersystem crossing while maintaining device stability and long operational lifetime
3Ease of operation
If low driving voltage is used, then ease of operation is improved, but luminescent efficiency and stability deteriorate
Solution Approach 1:
The patent modifies the HOMO-LUMO energy levels of host materials through heterocyclic group introduction, enabling low driving voltage operation while maintaining high luminescent efficiency and driving stability
Solution Approach 2:
The patent introduces specific functional groups (N, O, S heteroatoms in aromatic rings) at strategic positions in the molecular structure to locally enhance electron-hole recombination efficiency while maintaining overall device stability at low operating voltages
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 configuration achieves high luminescent efficiency and extended lifetime with low driving voltage, outperforming previous designs by optimizing the host materials and dopant usage in the light emitting layers.
Implementation Method 1
PTL 2 discloses an organic EL element exploiting TADF (Thermally Activated Delayed Fluorescence) mechanism. The TADF mechanism is to utilize the phenomenon of reverse intersystem crossing from triplet excitons to singlet excitons in a material having a small energy difference between the singlet level and the triplet level.
Implementation Method 2
By applying voltage to an organic EL element, holes and electrons are injected into a light emitting layer from an anode and a cathode, respectively. In the light emitting layer, injected holes and electrons recombine to generate excitons.
Implementation Method 3
it is known that when intersystem crossing is efficiently carried out from singlet excitons in a phosphorescent type organic EL element that utilizes luminescence from triplet excitons, the internal quantum efficiency may be increased to 100%.
Data Source
Figure 1
AI summary
Provided is an organic electroluminescence (organic EL) element having high luminescent efficiency and long lifetime with low driving voltage. An organic EL element including a light emitting layer between an anode and a cathode opposing each other, wherein the light emitting layer contains: a host material containing a first host and a second host; and a luminescence dopant material, the first host is a tetracyclic condensed aromatic heterocyclic compound that is represented by the following general formula (1) and contains, as heteroatoms, two N atoms or one N atom and one O or S atom, and the second host is a carbazole compound that is represented by the following general formula (2) and has, as a substituent, a tricyclic condensed aromatic heterocycle containing, as a heteroatom, one N, O or S atom.