Light-emitting element with lower triplet host
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Solution Overview
Problem
Conventional light-emitting elements using phosphorescent compounds with high emission energy require host materials with higher triplet levels, which compromises the reliability of the device, as the host material's reliability decreases with increased triplet level.
Innovation Solution
A light-emitting element structure featuring a host material with a lower triplet level than the guest material, where energy transfer is facilitated by a multicomponent decay curve and emission lifetime between 5 μsec and 15 μsec, allowing for high emission efficiency and reliability without the need for high triplet level host materials.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If a phosphorescent compound with high emission energy is used as a guest material, then the emission efficiency is improved, but the host material reliability decreases because higher triplet level host materials are required
Solution Approach 1:
The patent changes the emission lifetime parameter of the guest material to be in the range of 5-15 μsec, which enables energy transfer from host to guest even when the host T1 level is lower than the guest T1 level. This parameter change resolves the contradiction by allowing high emission efficiency with reliable host materials that have lower triplet levels.
Solution Approach 2:
The patent inverts the conventional requirement by allowing the host material T1 level to be lower than the guest material T1 level, contrary to the traditional approach. This inversion is achieved by controlling the emission lifetime to 5-15 μsec, which enables reverse energy transfer and resolves the contradiction between emission efficiency and host material reliability.
2Reliability
If the emission lifetime is extended to improve energy transfer, then the thermal deactivation process is suppressed, but the emission efficiency may be reduced if the lifetime becomes too long
Solution Approach 1:
The patent optimizes the emission lifetime parameter to a specific range of 5-15 μsec, which is long enough to suppress thermal deactivation processes but short enough to maintain high emission efficiency. This precise parameter control resolves the contradiction between suppressing thermal deactivation and maintaining emission 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
This configuration enables the use of materials with high reliability as host materials, maintaining high emission efficiency and extending the lifetime of the light-emitting element while allowing for the use of lower triplet level host materials, thus improving the overall reliability of the device.
Implementation Method 1
energy transfer from the host material to the guest material is possible even when the T1 level of the host material is lower than the T1 level of the guest material
Implementation Method 2
luminescence from the triplet excited state (T1) is referred to as phosphorescence
Implementation Method 3
the emission lifetime is short enough to prevail the thermal deactivation process of the host material
Implementation Method 4
electrons injected from a cathode and holes injected from an anode form an excited state in an emission region of the EL layer, and energy is released and light is emitted when the excited state returns to a ground state
Data Source
AI summary
Provided is a light-emitting element having a light-emitting layer which contains at least a host material and a plurality of guest materials, where the host material has a lower T1 level than that of at least one of the plurality of guest materials. The emission of the one of the plurality of guest materials exhibits a multicomponent decay curve, and the lifetime thereof is less than or equal to 15 μsec, preferably less than or equal to 10 μsec, more preferably less than or equal to 5 μsec, where the lifetime is defined as a time for the emission to decrease in intensity to 1/100 of its initial intensity.