Organic EL Emitting Layer with Fluorescent Dopant for High-Current Efficiency
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Solution Overview
Problem
Existing organic electroluminescent devices using delayed fluorescence mechanisms face efficiency roll-off in high current density areas, limiting their practical application.
Innovation Solution
Incorporating a specific compound as a first material and a fluorescent dopant material in the emitting layer to enhance light emission efficiency in high current density areas.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If delayed fluorescence mechanism (TTF or TADF) is used to improve internal quantum efficiency, then internal quantum efficiency can be raised up to 40-100%, but luminous efficiency rolls off in high current density areas
Solution Approach 1:
The patent changes the energy level parameters of the host material by selecting a compound with a small energy gap (ΔST) between singlet and triplet levels. This parameter change enables efficient inverse intersystem crossing from triplet to singlet excitons, achieving high internal quantum efficiency while maintaining stable luminous efficiency in high current density areas through optimized energy level matching between host and dopant materials.
Solution Approach 2:
The patent uses a composite material system consisting of a host material (compound of formula 1) and a fluorescent dopant material. This composite approach allows the host material to generate triplet excitons that undergo inverse intersystem crossing to singlet excitons, which then transfer energy to the dopant for fluorescent emission, achieving both high internal quantum efficiency and stable luminous efficiency at high current densities.
2Loss of energy
If phosphorescent emission is used to achieve 100% internal quantum efficiency, then internal quantum efficiency is improved, but device complexity and material stability become problematic
Solution Approach 1:
The patent replaces long-lived triplet excitons in phosphorescent devices with short-lived singlet excitons generated through delayed fluorescence mechanism. This substitution eliminates the need for heavy metal complexes and phosphorescent materials, reducing device complexity and improving material stability while achieving comparable internal quantum efficiency through the TADF mechanism in the host material.
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 organic electroluminescent device achieves efficient light emission with a delayed fluorescence ratio greater than 37.5% and maintains residual strength over 36.0% after voltage removal, addressing the efficiency roll-off issue.
Implementation Method 1
The TTF mechanism utilizes a phenomenon in which singlet excitons are generated by collision between two triplet excitons
Implementation Method 2
The TADF mechanism utilizes a phenomenon in which inverse intersystem crossing from triplet excitons to singlet excitons is generated by using a material having a small energy gap (ΔST) between the singlet level and the triplet level
Implementation Method 3
inverse intersystem crossing from triplet excitons to singlet excitons is generated by using a material having a small energy gap (ΔST) between the singlet level and the triplet level
Implementation Method 4
When voltage is applied on an organic electroluminescence device (hereinafter, referred to as an organic EL device), holes and electrons are respectively injected into an emitting layer from an anode and a cathode. The injected holes and electrons are recombined in the emitting layer to form excitons.
Data Source
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AI summary
An organic electroluminescence device according to an aspect of the invention includes: a cathode; an anode; and an organic thin-film layer disposed between the cathode and the anode, the organic thin-film layer having one or more layers including an emitting layer, in which the emitting layer includes a first material represented by the following formula (1) and a second material in a form of a fluorescent dopant material.