Organic EL Emission Material for Blue Delayed Fluorescence Stability
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Solution Overview
Problem
Existing organic electroluminescent (EL) devices, particularly blue and delayed fluorescence devices, face challenges in achieving high emission efficiency and stability, with current technologies falling short of practical applications in displays and lighting.
Innovation Solution
Development of an emission material represented by specific general formulas, incorporating a polycyclic aromatic compound with an indolocarbazole backbone fused with a benzothiophene backbone, used in light-emitting layers to enhance efficiency and stability, combined with host materials like biscarbazole and tricarbazole compounds.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If phosphorescent organic EL device is used to enhance internal quantum efficiency up to 100%, then emission efficiency is improved, but device lifetime is insufficient particularly for blue devices
Solution Approach 1:
The patent changes the fundamental emission mechanism parameter from phosphorescence to delayed fluorescence (specifically TTF mechanism), which alters the exciton utilization pathway. This parameter change enables achieving high external quantum efficiency (40% or more) without relying on phosphorescent materials, thereby improving device lifetime while maintaining energy efficiency
Solution Approach 2:
The patent employs composite material design by combining specific host materials (compounds 1-10) with guest materials (compounds 11-20) in the light-emitting layer. This composite structure enables the TTF mechanism to operate effectively, achieving both high efficiency and improved stability through synergistic material interactions
2Use of energy by moving object
If delayed fluorescence organic EL device utilizing TTF mechanism is used, then internal quantum efficiency can be enhanced up to 40%, but emission efficiency is lower compared to phosphorescent organic EL device
Solution Approach 1:
The patent optimizes the energy level parameters of the host and guest materials to enable efficient triplet-triplet fusion. By carefully selecting materials with appropriate HOMO-LUMO gaps and triplet energy levels, the device achieves external quantum efficiency of 40% or more, surpassing conventional delayed fluorescence devices
Solution Approach 2:
The patent introduces specific functional groups and molecular structures (compounds 1-10 as hosts and 11-20 as guests) with optimized local electronic properties. These localized structural optimizations enable efficient exciton management and radiative decay, achieving high emission efficiency in the delayed fluorescence mechanism
3Adaptability or versatility
If organic EL device is applied to display device such as flat panel display, then practical application is enabled, but emission efficiency needs to be improved and driving stability needs to be ensured
Solution Approach 1:
The patent optimizes key parameters including photoluminescence quantum yield (40% or more), CIE color coordinates, and device external quantum efficiency. These parameter optimizations enable the device to meet display application requirements while achieving high emission efficiency
Solution Approach 2:
The patent employs composite material systems with specific host-guest combinations that provide both the efficiency required for practical display applications and the stability needed for driving. The composite structure enables simultaneous optimization of multiple performance parameters
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 emission material achieves high emission efficiency with a photoluminescence quantum yield of 40% or more, particularly in the blue and cyan spectral regions, providing a practically useful organic EL device with improved stability and efficiency.
Implementation Method 1
Patent Literature 2 discloses an organic EL device utilizing the Thermally Activated Delayed Fluorescence (TADF) mechanism. The TADF mechanism utilizes a phenomenon in which reverse intersystem crossing occurs from the triplet exciton to the singlet exciton
Implementation Method 2
The TADF mechanism utilizes a phenomenon in which reverse intersystem crossing occurs from the triplet exciton to the singlet exciton in a material having a small energy difference between the singlet level and the triplet level
Implementation Method 3
Patent Literature 1 discloses an organic EL device utilizing the Triplet-Triplet Fusion (TTF) mechanism, which is one of the mechanisms of delayed fluorescence. The TTF mechanism utilizes a phenomenon in which a singlet exciton is generated by the collision of two triplet excitons
Implementation Method 4
it has been known that, in the phosphorescent organic EL device that uses emission caused by triplet excitons, the internal quantum efficiency can be enhanced up to 100% when intersystem crossing efficiently occurs from singlet excitons
Implementation Method 5
In the fluorescent organic EL device that uses emission caused by singlet excitons, the limit of the internal quantum efficiency is said to be 25%
Implementation Method 6
in the phosphorescent organic EL device that uses emission caused by triplet excitons, the internal quantum efficiency can be enhanced up to 100%
Data Source
AI summary
Provided are an emission material that can be used to obtain an organic EL device having high emission efficiency and a long lifetime, and an organic EL device including the emission material. Specifically, provided are an emission material represented by the following general formula (1) and an organic EL device including the emission material: wherein each A1 independently represents CR1, C or N and each R1 independently represents hydrogen or the like, provided that the number of N present in one 6-membered ring containing A1 is 2 or less; a ring E represents a heterocycle represented by formula (1a), and is fused with an adjacent ring at any position; and a, b, c, and d each independently represent 0 or 1, and there is no occurrence in which all a, b, c and d represent 0.