Host-Guest Light-Emitting Element for High External Quantum Efficiency
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Solution Overview
Problem
Existing organic electroluminescence (EL) elements have limited external quantum efficiency, typically ranging from 20% to 30%, due to light absorption by electrodes and concentration quenching in phosphorescent compounds.
Innovation Solution
A light-emitting element is designed with a light-emitting layer comprising a guest material and a host material, where the emission spectrum of the host material overlaps with the absorption spectrum of the guest material, facilitating the conversion of excitation energy for enhanced phosphorescence emission.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If phosphorescent compounds are used in the light-emitting layer, then internal quantum efficiency can reach 100%, but concentration quenching occurs reducing external quantum efficiency to 20-30%
Solution Approach 1:
The patent introduces a host material as an intermediary between the phosphorescent guest material and the electrodes. The host material absorbs excitation energy and transfers it to the guest material, preventing direct excitation of the phosphorescent compound and thereby reducing concentration quenching. This mediator approach enables the system to achieve both high internal quantum efficiency through phosphorescence and improved external quantum efficiency by minimizing energy loss pathways.
2Illumination intensity
If phosphorescent compound concentration is increased to enhance emission intensity, then brightness increases, but concentration quenching increases reducing efficiency
Solution Approach 1:
The patent creates a heterogeneous structure where phosphorescent guest material is dispersed as individual molecules or small clusters within the host material matrix. This spatial distribution ensures that while the overall concentration of phosphorescent material is sufficient for strong emission, the local concentration at any given point remains low enough to avoid concentration quenching. Different regions of the light-emitting layer maintain optimal local properties for both emission intensity and efficiency.
3Use of energy by moving object
If triplet excited states are utilized for phosphorescence, then internal quantum efficiency improves, but triplet-triplet annihilation occurs reducing overall efficiency
Solution Approach 1:
The patent segments the excitation energy distribution by utilizing the host material to absorb initial excitation and then transfer energy individually to dispersed guest material molecules. This segmentation prevents multiple triplet excitations from occurring in close proximity, thereby minimizing triplet-triplet annihilation events. The host-guest system effectively divides the energy transfer process into discrete, spatially separated events rather than allowing concentrated triplet state interactions.
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 achieves high external quantum efficiency and prolongs the lifetime of the light-emitting element by optimizing energy transfer and reducing deactivation processes.
Implementation Method 1
an emission spectrum of the host material overlaps with an absorption spectrum of the guest material, and phosphorescence is emitted by conversion of an excitation energy of the host material into an excitation energy of the guest material
Implementation Method 2
light emission from the triplet excited state (T*) is referred to as phosphorescence where electron transition occurs between different spin multiplicities
Implementation Method 3
light emission from the singlet excited state (S*) is referred to as fluorescence because it is caused by electron transition between the same spin multiplicities
Data Source
AI summary
Provided is a light-emitting element with high external quantum efficiency, or a light-emitting element with a long lifetime. The light-emitting element includes, between a pair of electrodes, a light-emitting layer including a guest material and a host material, in which an emission spectrum of the host material overlaps with an absorption spectrum of the guest material, and phosphorescence is emitted by conversion of an excitation energy of the host material into an excitation energy of the guest material. By using the overlap between the emission spectrum of the host material and the absorption spectrum of the guest material, the energy smoothly transfers from the host material to the guest material, so that the energy transfer efficiency of the light-emitting element is high. Accordingly, a light-emitting element with high external quantum efficiency can be achieved.