Host Material for Phosphorescent OLED Efficiency and Lifetime
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Solution Overview
Problem
Current organic electroluminescence devices face challenges in achieving high efficiency and long lifetime due to the lack of effective host materials that can efficiently transfer energy to phosphorescent materials and maintain stability.
Innovation Solution
The use of compounds with two or more condensed polycyclic aromatic rings serially bonded to a fluorene skeleton, or with different condensed polycyclic aromatic rings bonded to a fluorene, dibenzofuran, or dibenzothiophene skeleton, which act as host materials in the organic electroluminescence device, allowing for efficient energy transfer and extended conjugated systems.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If CBP is used as a host material, then current efficiency is drastically enhanced, but lifetime becomes very short
Solution Approach 1:
The patent modifies the molecular structure parameters of the host material by introducing condensed ring derivatives with nitrogen-containing rings (carbazole, triphenylene, phenanthrene structures) to enhance oxidation resistance while maintaining high triplet energy levels, thereby resolving the contradiction between efficiency and lifetime
Solution Approach 2:
The patent creates composite host materials by combining multiple structural elements (condensed rings, nitrogen-containing heterocycles, aromatic hydrocarbons) to achieve both high current efficiency through effective energy transfer and long lifetime through oxidation resistance
2Adaptability or versatility
If anthracene derivative is used as a host material, then it is suitable for fluorescent emission, but it cannot transfer energy to phosphorescent dopant and confine excited triplet energy
Solution Approach 1:
The patent changes the triplet energy parameter of the host material by incorporating nitrogen-containing heterocyclic structures and condensed ring systems, raising the triplet energy level above 2.1 eV to enable effective energy transfer to phosphorescent dopants while maintaining structural stability
3Reliability
If aromatic hydrocarbon compound with highly symmetric rigid molecular structure is used, then it can be used as phosphorescent host, but light emitting layer is likely to crystallize
Solution Approach 1:
The patent introduces asymmetric substitution patterns and varied alkyl chain lengths/branches to disrupt molecular symmetry and packing, preventing crystallization of the light emitting layer while maintaining the phosphorescent host capability through high triplet energy levels
Solution Approach 2:
The patent applies different functional groups and substituent patterns at specific positions of the molecular structure to locally modify properties, enhancing both phosphorescent performance and amorphous stability without compromising overall device function
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 approach results in a phosphorescent organic EL device with improved driving voltage, lifetime, and efficiency, specifically enabling high-efficiency green-emitting phosphorescent emission by effectively transferring energy to phosphorescent dopants while maintaining material stability.
Implementation Method 1
the excited triplet energy Eg (T) of the host material has to be larger than the excited triplet energy Eg (S) of the phosphorescent dopant
Implementation Method 2
a light emitting material (phosphorescent material) which emits light from triplet exciton has been developed
Implementation Method 3
An organic EL device, which has an organic thin film layer including a light emitting layer between an anode and a cathode and which emits light from an exciton energy resulted from the recombination of holes and electrons injected into the light emitting layer
Data Source
Figure 1
AI summary
Disclosed is an organic electroluminescent element which is characterized by comprising a cathode, an anode, and a monolayered or multilayered organic thin film layer, wherein the organic thin film layer comprises one or more light-emitting layers, and wherein at least one of the light-emitting layers comprises at least one phosphorescent material that can emit a phosphorescence and a host material that is a compound essentially having a structure composed of a fluorine, dibenzofuran or dibenzothiophene skeleton and a naphthalene ring bound to the skeleton. The organic electroluminescent element has a high efficiency, a long service life, and phosphorescence-emitting properties. Also disclosed is a material for an organic electroluminescent element, which can be used for the above-mentioned organic electroluminescent element.