OLED Emitting Layer Host Composition for Low-Voltage Stability
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Solution Overview
Problem
Existing organic electroluminescent devices face challenges in achieving high efficiency and stability, particularly in extending the lifespan and improving luminous efficiency while maintaining a low driving voltage.
Innovation Solution
Incorporating a specific oligopyridine compound as a first host and a carbazole compound as a second host in the light-emitting layer, along with a hole blocking layer, to control charge injection and transport, thereby enhancing device characteristics such as efficiency and stability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If a phosphorescent organic electroluminescent device is used to achieve 100% internal quantum efficiency through triplet excitons, then luminous efficiency is improved, but device lifespan is reduced
Solution Approach 1:
The patent changes the emission mechanism parameter from phosphorescence (triplet exciton utilization) to delayed fluorescence (TTF mechanism), where singlet excitons are generated through collision of two triplet excitons. This parameter change maintains high internal quantum efficiency (theoretically 40% or higher) while avoiding the lifespan issues inherent in phosphorescent devices
Solution Approach 2:
The patent employs a composite host system consisting of a TTF mechanism host material combined with specific dopant materials. This composite material approach enables efficient triplet-triplet fusion while providing stable device operation, resolving the contradiction between efficiency and lifespan
2Use of energy by moving object
If a TADF mechanism is used to achieve 100% internal quantum efficiency through reverse intersystem crossing, then luminous efficiency is improved, but device lifespan characteristics are insufficient
Solution Approach 1:
The patent selects the TTF mechanism over TADF by changing the exciton utilization parameter. In TTF, singlet excitons are generated directly through triplet-triplet fusion, whereas TADF relies on reverse intersystem crossing. This parameter change achieves high efficiency while providing superior device lifespan characteristics
Solution Approach 2:
The patent adopts the TTF mechanism which has been shown to provide both high efficiency and good lifespan, effectively copying the successful approach from prior art (Patent Literature 1) while optimizing the specific host and dopant materials to further improve device characteristics
3Device complexity
If conventional host materials are used in organic electroluminescent devices, then device structure is simple, but efficiency and driving stability are insufficient
Solution Approach 1:
The patent uses a composite host system comprising a TTF mechanism host material and specific dopant materials. This composite approach achieves high luminous efficiency and driving stability while maintaining reasonable device structure, resolving the contradiction between simplicity and performance
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 oligopyridine and carbazole compounds in the light-emitting layer results in high efficiency and extended lifespan of the organic electroluminescent devices, with improved luminous efficiency and driving stability at a low voltage.
Implementation Method 1
Application of a voltage to an organic electroluminescent device allows injection of holes and electrons from an anode and a cathode, respectively, into a light-emitting layer
Implementation Method 2
Injected holes and electrons recombine to generate excitons in the light-emitting layer
Implementation Method 3
Application of a voltage to an organic electroluminescent device allows injection of holes and electrons from an anode and a cathode, respectively, into a light-emitting layer. Then, in the light-emitting layer, injected holes and electrons recombine to generate excitons
Implementation Method 4
Regarding a phosphorescent organic electroluminescent device using light emission from triplet excitons, it is known that intersystem crossing is efficiently performed from singlet excitons
Implementation Method 5
The TADF mechanism utilizes a phenomenon in which reverse intersystem crossing from triplet excitons to singlet excitons is generated in a material having a small energy difference between a singlet level and a triplet level
Implementation Method 6
highly efficient organic electroluminescent devices utilizing delayed fluorescence have been developed
Implementation Method 7
The TTF mechanism utilizes a phenomenon in which singlet excitons are generated due to collision of two triplet excitons
Data Source
AI summary
To provide an organic electroluminescent device having high efficiency and high driving stability while having a low driving voltage. The organic electroluminescent device has one or more light-emitting layers between an anode and a cathode opposed to each other, wherein at least one of the light-emitting layers is a light-emitting layer composed of a vapor deposition layer containing a first host, a second host and a light-emitting dopant material; the first host is selected from oligopyridine compounds represented by the general formula (1); and the second host is selected from carbazole compounds having two or more carbazole rings, indolocarbazole compounds having an indolocarbazole ring or compounds having a carbazole ring and an indolocarbazole ring.