Organic EL Host Melt Mixture for Low-Voltage Long-Life Emission
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Solution Overview
Problem
Existing organic electroluminescent (EL) devices face challenges in achieving high efficiency, prolonged lifespan, and stability while maintaining low driving voltage, particularly in phosphorescent and thermally activated delayed fluorescence (TADF) mechanisms.
Innovation Solution
A melt mixture of two organic compounds with a vapor deposition temperature difference of 20°C or less and a fluorescence emission wavelength difference within ±10 nm is used to form a light-emitting layer, enhancing energy transfer and improving luminous efficiency and lifespan.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If phosphorescent organic EL devices use triplet excitons for light emission, then internal quantum efficiency is raised to 100%, but lifespan is prolonged poorly
Solution Approach 1:
The patent changes the energy level parameters of the host materials by selecting specific compounds with carefully matched LUMO levels. The first host material has a LUMO level of 2.0-3.0 eV and the second host material has a LUMO level of 1.5-2.5 eV, creating optimal energy transfer conditions that improve device lifespan while maintaining efficiency
Solution Approach 2:
The patent employs a composite host system using two different organic compounds instead of a single host material. This dual-host composite structure enables synergistic effects where one host material facilitates efficient energy transfer and the other provides enhanced stability, simultaneously addressing both efficiency and lifespan requirements
2Use of energy by moving object
If TADF mechanism is used with small energy difference between singlet and triplet levels, then internal quantum efficiency is raised to 100%, but lifespan characteristics require further improvement
Solution Approach 1:
The patent optimizes the energy gap parameter between singlet and triplet states by selecting dopant materials with specific energy characteristics. The dopant is chosen to have an energy gap that enables efficient reverse intersystem crossing while generating delayed fluorescence, achieving high internal quantum efficiency through parameter optimization
Solution Approach 2:
The patent introduces a mediator mechanism through the dual-host system where energy is transferred from the first host to the second host, and then to the dopant. This intermediary energy transfer pathway facilitates efficient TADF while reducing direct stress on the dopant molecules, thereby improving lifespan characteristics
3Power
If organic EL devices achieve high efficiency, then luminous output increases, but driving voltage stability deteriorates
Solution Approach 1:
The patent changes the HOMO and LUMO level parameters of the host materials to optimize charge injection and transport. The first host material has HOMO level of 5.5-6.5 eV and LUMO level of 2.0-3.0 eV, while the second host material has HOMO level of 5.0-6.0 eV and LUMO level of 1.5-2.5 eV. These parameter adjustments enable efficient charge carrier generation and transport, achieving high luminous efficiency with stable driving voltage
Solution Approach 2:
The composite dual-host system provides complementary functions: one host material optimizes for charge injection and the other for charge transport. This division of functional responsibilities within the composite material system maintains stable driving voltage while achieving high overall device efficiency
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 organic EL device achieves high luminous efficiency and prolonged lifespan with a low driving voltage by optimizing the mixture of organic compounds in the light-emitting layer.
Implementation Method 1
a melt mixture of two organic compounds with a vapor deposition temperature difference of 20°C or less
Implementation Method 2
vapor deposition temperature
Implementation Method 3
When a voltage is applied to an organic EL device, holes are injected from an anode and electrons are injected from a cathode to a light-emitting layer, respectively. Thus, in the light-emitting layer, injected holes and electrons recombine to generate excitons.
Implementation Method 4
in a phosphorescent organic EL device using light emission from triplet excitons, when intersystem crossing is efficiently performed from singlet excitons, the internal quantum efficiency is raised to 100%
Implementation Method 5
The TTF mechanism utilizes a phenomenon in which singlet excitons are generated due to collision of two triplet excitons, and it is thought that the internal quantum efficiency is theoretically raised to 40%
Implementation Method 6
two types of organic compounds are melted and mixed to produce an organic alloy having a maximum emission wavelength of a fluorescence-emitting spectrum different from a maximum emission wavelength of a fluorescence-emitting spectrum of each individual organic compound
Data Source
Figure 1~2
Figure 3~4
AI summary
Provided are an organic EL device having high luminous efficiency and a prolonged lifespan with a low driving voltage, and a melt mixture for an organic electroluminescent device used in the organic EL device. The melt mixture for an organic electroluminescent device is a melt mixture of at least two types of organic compounds including a first organic compound and a second organic compound, and a difference in vapor deposition temperature between the first organic compound and the second organic compound is 20°C or less, and a difference between a PL maximum emission wavelength of the melt mixture and a PL maximum emission wavelength of any of the first organic compound and the second organic compound is within ±10 nm. The melt mixture is suitable as a host material of a light-emitting layer.