Light Emission Material for OLED Efficiency and Roll-off Reduction
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Solution Overview
Problem
Existing organic electroluminescence devices face limitations in achieving high efficiency and durability, with fluorescent devices struggling to exceed 5% external quantum efficiency and phosphorescent devices experiencing weak driving durability.
Innovation Solution
A light emission material is developed, comprising a first compound that satisfies specific equations regarding radiationless transition rates and reverse intersystem crossing, and optionally a second compound with a higher triplet excitation energy level than the singlet excitation energy level of the first compound, to enhance efficiency and reduce roll-off.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a fluorescent organic electroluminescence device is used, then the device structure is simple and ease of manufacture is improved, but external quantum efficiency is limited to about 5% or less
Solution Approach 1:
The patent changes the key parameter of transition rates by selecting a compound where the reverse intersystem crossing transition rate (K2) is at least 0.1 times the radiationless transition rate (K1). This parameter change enables efficient triplet-to-singlet conversion, allowing fluorescent devices to achieve external quantum efficiency of 5% or more while maintaining the simple device structure and manufacturing ease of fluorescent OLEDs.
2Productivity
If a phosphorescent organic electroluminescence device is used, then external quantum efficiency is improved, but driving durability becomes weak
Solution Approach 1:
The patent introduces a specific compound as an intermediary in the emission layer that mediates the conversion between triplet and singlet excitons. This intermediary compound enables efficient light emission through reverse intersystem crossing without requiring phosphorescent materials, thus achieving high external quantum efficiency while avoiding the poor driving durability associated with phosphorescent OLEDs.
3Productivity
If high efficiency is achieved in fluorescent OLEDs, then external quantum yield increases, but roll-off phenomenon occurs at high brightness
Solution Approach 1:
The patent utilizes the dynamic nature of exciton conversion by selecting a compound with appropriate reverse intersystem crossing transition rate (K2) that can adapt to different operating conditions. The dynamic balance between triplet-to-singlet conversion and other deactivation pathways allows the device to maintain high external quantum yield across a wide brightness range, suppressing the roll-off phenomenon that typically occurs in high-efficiency fluorescent OLEDs.
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 light emission material achieves high efficiency with a maximum external quantum yield of 5% or more and minimizes the roll-off phenomenon, thereby improving the performance of organic electroluminescence devices.
Implementation Method 1
K2 is a reverse intersystem crossing transition rate from the certain specific n-th triplet excitation state to a singlet excitation state which is adjacent to the n-th triplet excitation state
Implementation Method 2
The organic electroluminescence device emits light using light generated during the transition of the excitons to a ground state
Data Source
AI summary
A light emission material includes a first compound satisfying Equation 1:K2≥0.1K1. Equation 1In Equation 1, K1 is a sum of radiationless transition rate due to internal conversion from a certain specific n-th triplet excitation state to a lower order triplet excitation state including the lowest triplet excitation state, K2 is a reverse intersystem crossing transition rate from the certain specific n-th triplet excitation state to a singlet excitation state which is adjacent to the n-th triplet excitation state, and n is an integer of 2 or more. An organic electroluminescence device including the light emission material may simultaneously attain high emission efficiency and roll-off reduction.