OLED Emitting Layer Composition Using TADF-Phosphor Energy Transfer
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Solution Overview
Problem
Organic electroluminescence (EL) elements face limitations in external quantum efficiency and drive voltage, particularly when using phosphorescent compounds, with light extraction efficiency around 20-30% and external quantum efficiency capped at 25% due to factors like concentration quenching and triplet-triplet annihilation.
Innovation Solution
Incorporating a thermally activated delayed fluorescence (TADF) material in the light-emitting layer, where the fluorescence spectrum of the TADF material overlaps with the absorption spectrum of the phosphorescent compound, enhancing energy transfer and emission efficiency while maintaining low drive voltage.
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 be increased to 100%, but external quantum efficiency is limited to approximately 25% due to light extraction efficiency of 20-30%
Solution Approach 1:
The patent introduces a TADF material as an intermediary substance between the phosphorescent compound and the host material. This TADF material facilitates energy transfer through its fluorescence spectrum overlapping with the absorption spectrum of the phosphorescent compound, enabling more efficient energy transfer and improving external quantum efficiency while maintaining high internal quantum efficiency.
2Reliability
If phosphorescent compounds are dispersed in a host material matrix, then concentration quenching and triplet-triplet annihilation are suppressed, but device complexity increases due to multi-component system requirements
Solution Approach 1:
The patent creates a composite light-emitting layer containing three components: host material, phosphorescent compound, and TADF material. This composite structure leverages the complementary properties of each component - the host material provides the matrix, the phosphorescent compound provides high efficiency emission, and the TADF material enhances energy transfer while suppressing quenching effects.
3Productivity
If the fluorescence spectrum of TADF material overlaps with absorption spectrum of phosphorescent compound, then energy transfer is enhanced and external quantum efficiency increases, but drive voltage increases due to additional energy transfer requirements
Solution Approach 1:
The patent optimizes the energy level parameters of the TADF material by selecting materials whose fluorescence spectrum strategically overlaps with the absorption spectrum of the phosphorescent compound. This parameter optimization enhances energy transfer efficiency while minimizing the energy gap, thereby improving external quantum efficiency without excessively increasing drive voltage.
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 significantly increases external quantum efficiency and reduces drive voltage, leading to higher emission efficiency and longer lifetimes in organic EL elements by optimizing energy transfer and minimizing deactivation processes.
Implementation Method 1
Incorporating a thermally activated delayed fluorescence (TADF) material in the light-emitting layer, where the fluorescence spectrum of the TADF material overlaps with the absorption spectrum of the phosphorescent compound
Implementation Method 2
the phosphorescent compound exhibits phosphorescence in the light-emitting layer by voltage application between the pair of electrodes
Implementation Method 3
An organic EL element has been actively researched and developed. In a fundamental structure of the organic EL element, a light-emitting layer containing a light-emitting material is interposed between a pair of electrodes
Data Source
AI summary
Provided is a light-emitting element with high external quantum efficiency and a low drive voltage. The light-emitting element includes a light-emitting layer which contains a phosphorescent compound and a material exhibiting thermally activated delayed fluorescence between a pair of electrodes, wherein a peak of a fluorescence spectrum and/or a peak of a phosphorescence spectrum of the material exhibiting thermally activated delayed fluorescence overlap(s) with a lowest-energy-side absorption band in an absorption spectrum of the phosphorescent compound, and wherein the phosphorescent compound exhibits phosphorescence in the light-emitting layer by voltage application between the pair of electrodes.