TADF Organic Compound for OLED Efficiency and Lifetime
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Solution Overview
Problem
Current phosphorescent materials for organic light-emitting diodes (OLEDs) are costly due to the use of expensive metals like iridium, and thermally activated delayed fluorescent (TADF) materials have long luminescence lifetimes that lead to decreased light emission efficiency and durability issues in displays.
Innovation Solution
An organic compound with a specific energy gap (ΔEST) of −0.20 eV to 0.0090 eV and a radiative decay rate constant of 1.0×10^6 s^-1, which is a heptazine derivative with arbitrary substituents, is used to enhance reverse intersystem crossing and reduce luminescence lifetime, improving light emission efficiency and durability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If phosphorescent materials containing expensive metals like iridium are used, then internal quantum efficiency can be increased to theoretical levels, but the cost of the organic light emitting device increases significantly
Solution Approach 1:
The patent replaces expensive phosphorescent materials containing iridium with inexpensive TADF materials that have short luminescence lifetimes. This substitution achieves high internal quantum efficiency without the high cost of precious metals, directly resolving the contradiction between efficiency and manufacturing cost
Solution Approach 2:
The patent modifies the energy gap parameter (ΔEST) of the TADF material to be within a specific range (0.01 eV or less, preferably 0.005 eV or less). By optimizing this energy parameter, the material achieves efficient reverse intersystem crossing and high internal quantum efficiency while maintaining the cost advantages of organic materials without precious metals
2Use of energy by moving object
If TADF materials with small energy gap ΔEST are used to promote reverse intersystem crossing, then internal quantum efficiency increases, but luminescence lifetime becomes excessively long causing deterioration and decreased light emission efficiency
Solution Approach 1:
The patent optimizes two critical parameters simultaneously: the energy gap ΔEST is reduced to 0.01 eV or less to promote reverse intersystem crossing, while the luminescence lifetime is controlled to be 1 ns or more but not excessively long. This dual parameter optimization resolves the contradiction by achieving high efficiency without the detrimental effects of overly long lifetimes
Solution Approach 2:
The patent creates a dynamic balance in the excited state transitions by tuning the energy levels. The small ΔEST enables rapid reverse intersystem crossing for high efficiency, while the controlled luminescence lifetime prevents triplet exciton accumulation. This dynamic optimization allows the material to operate efficiently without suffering from the drawbacks of long-lived excited states
3Loss of energy
If TADF materials with long luminescence lifetime are used, then reverse intersystem crossing is promoted, but triplet exciton density increases causing deterioration and decreased light emission efficiency at high luminance
Solution Approach 1:
The patent precisely controls the energy gap ΔEST to be 0.01 eV or less, which optimizes the rate of reverse intersystem crossing. This parameter control ensures that triplet excitons are efficiently converted to singlet excitons before they can accumulate to damaging levels, thereby maintaining both high energy conversion efficiency and material durability
Solution Approach 2:
The patent establishes a feedback mechanism where the small energy gap enables rapid monitoring and conversion of triplet excitons back to singlet states. This continuous conversion process prevents the accumulation of harmful triplet excitons, creating a self-regulating system that maintains reliability while achieving efficient energy utilization
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 compound shortens luminescence lifetime, increases light emission intensity, and enhances the drive lifetime of OLEDs, making it suitable for use in displays while avoiding the high costs and inefficiencies of traditional phosphorescent materials.
Implementation Method 1
The TADF material utilizes the lowest triplet excitation state T1, in which the TADF material loses its activity as heat otherwise, as delayed fluorescence by thermally inducing reverse intersystem crossing from the lowest triplet excitation state T1 to the lowest singlet excitation state S1
Implementation Method 2
the thermally activated delayed fluorescent material is referred to as 'TADF material'. The TADF material is configured such that an energy gap ΔEST obtained by subtracting an energy rank ET1 of a lowest triplet excitation state T1 from an energy level ES1 of a lowest singlet excitation state S1 is small
Implementation Method 3
An organic light emitting diode is an example of an organic light emitting device utilizing an organic electroluminescent (hereinafter referred to as 'organic EL') material constituted by an organic compound
Data Source
AI summary
In order to provide an organic compound that can be suitably used as a luminescent material for a display, and an organic light emitting device containing such an organic compound, an organic compound in accordance with an embodiment of the present invention has a lone electron-pair and a π E electron orbit, and in the organic compound, an energy gap ΔEST obtained by subtracting an energy level ET1 of a lowest triplet excitation state T1 from an energy level ES1 of a lowest singlet excitation mode S1 is −0.20 eV≤ΔEST<0.0090 eV.