OLED Host Melt Mixture for Low-Voltage Efficiency and Lifespan
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Solution Overview
Problem
Organic electroluminescent devices face limitations in internal quantum efficiency and lifespan, particularly in phosphorescent and delayed fluorescence mechanisms, requiring improvements in luminous efficiency and driving stability while maintaining low driving voltage.
Innovation Solution
A melt mixture of two organic compounds with a vapor deposition temperature difference of 20° C or less, where the difference in maximum emission wavelength between the mixture and individual compounds is within ±10 nm, is used to form a light-emitting layer through vacuum vapor deposition, enhancing energy transfer and stability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If phosphorescent organic EL devices are used to achieve high internal quantum efficiency through triplet excitons, then the internal quantum efficiency is raised to 100%, but the lifespan is prolonged insufficiently
Solution Approach 1:
The patent uses a composite host system comprising two different host materials (first host and second host) in specific weight ratios (first host: 30-70 wt%, second host: 70-30 wt%). This composite structure combines the advantages of both materials to achieve high internal quantum efficiency while improving device lifespan, resolving the contradiction between efficiency and durability in phosphorescent OLEDs.
2Use of energy by moving object
If TADF mechanism is used to achieve high internal quantum efficiency through reverse intersystem crossing, then the internal quantum efficiency is theoretically raised to 100%, but the lifespan characteristics require further improvement
Solution Approach 1:
The patent employs a composite host system with two different host materials optimized for TADF mechanisms. The specific composition ratio (first host: 30-70 wt%, second host: 70-30 wt%) enables efficient reverse intersystem crossing while simultaneously improving device lifespan, addressing the contradiction between high efficiency and durability in TADF-based OLEDs.
3Device complexity
If fluorescence-emitting organic EL device is used with singlet excitons, then the device structure is simpler, but the internal quantum efficiency is limited to 25%
Solution Approach 1:
The patent uses a composite host system that maintains relative structural simplicity while enabling phosphorescent or TADF emission mechanisms. The combination of two host materials allows the device to achieve high internal quantum efficiency (theoretically 100%) without significantly increasing device complexity, as the composite host integrates the necessary functional properties within the existing device architecture.
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 approach results in organic electroluminescent devices with high luminous efficiency and prolonged lifespan at low driving voltage, improving brightness and lifespan characteristics.
Implementation Method 1
a melt mixture of two organic compounds with a vapor deposition temperature difference of 20° C or less, where the difference in maximum emission wavelength between the mixture and individual compounds is within ±10 nm, is used to form a light-emitting layer through vacuum vapor deposition
Implementation Method 2
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 3
it is known that, 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 4
PTL 1 discloses an organic EL device using a Triplet-Triplet Fusion (TTF) mechanism which is one of delayed fluorescence mechanisms. The TTF mechanism utilizes a phenomenon in which singlet excitons are generated due to collision of two triplet excitons
Implementation Method 5
PTL 2 discloses an organic EL device using a thermally activated delayed fluorescence (TADF) mechanism. 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
Data Source
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.