Fluorene-Aromatic Host for Low-Voltage Phosphorescent OLEDs
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Solution Overview
Problem
Existing organic electroluminescence (EL) devices using phosphorescent materials face inefficiencies in luminous performance and require high driving voltages due to differences in electron affinity and ionization potential between layers, limiting their power consumption and longevity.
Innovation Solution
A fluorene-containing aromatic compound with a carbazole skeleton and nitrogen-containing heteroaromatic rings is used to reduce electron affinity differences, enhancing carrier transport and lowering the voltage required for phosphorescent organic EL devices, thereby improving luminous efficiency and device longevity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If phosphorescent materials are used in the emitting layer, then luminous efficiency can be improved by utilizing both singlet and triplet excited states, but driving voltage becomes excessively high due to electron affinity differences between layers
Solution Approach 1:
The patent modifies the molecular structure of the host material by incorporating electron-transporting moieties (such as pyridine, pyrimidine, triazine rings) directly into the carbazole core. This structural modification changes the electron affinity parameter of the host material, enabling it to match the electron affinity of the electron-transporting layer while maintaining high luminous efficiency with phosphorescent dopants.
Solution Approach 2:
The patent creates composite host materials by combining carbazole units with nitrogen-containing aromatic rings (pyridine, pyrimidine, triazine) within the same molecular structure. This composite approach allows the host material to simultaneously exhibit hole-transporting capability from carbazole and electron-transporting capability from the nitrogen-containing rings, thereby matching electron affinity with the electron-transporting layer and reducing driving voltage.
2Use of energy by moving object
If conventional host materials are used with phosphorescent dopants, then high luminous efficiency can be achieved, but device lifetime is limited due to high operating voltage
Solution Approach 1:
The patent changes the electron affinity parameter of the host material through molecular design, incorporating electron-transporting nitrogen-containing aromatic rings into the carbazole structure. This parameter change enables the host to match the electron affinity of the electron-transporting layer, reducing interfacial energy barriers and operating voltage, thereby extending device lifetime while maintaining high luminous efficiency.
3Speed
If the electron affinity difference between emitting layer and electron transporting layer is large, then carrier transport can be efficient, but the voltage required to drive the device becomes unacceptably high
Solution Approach 1:
The patent optimizes the electron affinity parameter of the host material by incorporating nitrogen-containing aromatic rings (pyridine, pyrimidine, triazine) into the carbazole structure. This creates a balanced electron affinity that matches the electron-transporting layer, eliminating excessive voltage requirements while maintaining efficient carrier transport through the emitting layer.
Solution Approach 2:
The patent designs the host material to perform multiple functions simultaneously: hole transport from carbazole units, electron transport from nitrogen-containing rings, and energy transfer to phosphorescent dopants. This multi-functionality allows the host to match electron affinity with the electron-transporting layer without sacrificing carrier transport efficiency, thereby reducing driving voltage.
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 use of the fluorene-containing aromatic compound enables organic EL devices with high luminous efficiency, long lifetime, and low voltage drivability, making them suitable for various applications including organic solar cells and sensors.
Implementation Method 1
With the exciton energy generated by the excitons being transferred to the dopant, the dopant can emit light with high efficiency.
Implementation Method 2
application of a phosphorescent material has been recently proposed for the emitting layer of the organic EL device. Thus, in the emitting layer of the organic EL device, a singlet state and a triplet state of excited states of an organic phosphorescent material are used to achieve a high luminous efficiency.
Implementation Method 3
An organic electroluminescence device (hereinafter, electroluminescence is occasionally abbreviated as EL) is a self-emitting device based on the principle that, when an electrical field is applied, a fluorescent material emits light using energy generated by a recombination of holes injected from an anode with electrons injected from a cathode.
Data Source
AI summary
A fluorene-containing aromatic compound represented by a formula (1) below.In the formula (1): Nr1 represents a substituted or unsubstituted monocyclic nitrogen-containing aromatic ring having 2 to 5 ring carbon atoms, or a bicyclic nitrogen-containing aromatic ring having 2 to 9 ring carbon atoms; Ar represents an aromatic ring and the like; Fl1 and Fl2 represent a fluorenyl group; and Cz1 and Cz2 represent a carbazolyl group. A compound represented by a formula (2) below is omitted from the fluorene-containing aromatic compound represented by the formula (1).