TADF Material for OLEDs with Fast Reverse Intersystem Crossing
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Solution Overview
Problem
Current organic electroluminescent devices (OLEDs) face limitations in achieving high internal quantum efficiency due to the low singlet-to-triplet exciton ratio, particularly with fluorescent materials, and the scarcity of thermally activated delayed fluorescence (TADF) materials with fast reverse intersystem crossing rates and broad spectral coverage from blue-green to orange-red light.
Innovation Solution
A blue-green to orange-red thermally activated delayed fluorescence material is synthesized using a compound represented by formula I, involving specific raw materials and a manufacturing method that includes mixing and reacting these materials with palladium acetate and tri-tert-butylphosphine tetrafluoroborate, followed by purification through column chromatography, to achieve ultra-fast reverse intersystem crossing and high luminous efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If fluorescent materials are used in OLEDs, then the device structure is simple and manufacturing is easier, but the internal quantum efficiency is limited to 25% due to the 1:3 singlet-to-triplet exciton ratio
Solution Approach 1:
The patent modifies the energy level parameters of the fluorescent material by introducing specific substituents (electron-donating or electron-withdrawing groups) to reduce the energy gap between singlet and triplet states, enabling thermal activation of triplet excitons and achieving delayed fluorescence with internal quantum efficiency exceeding 25%
Solution Approach 2:
The patent creates composite fluorescent TADF materials by combining electron donor and electron acceptor units with specific HOMO-LUMO energy level offsets, forming a system where charge transfer states facilitate reverse intersystem crossing from triplet to singlet excitons, thereby improving internal quantum efficiency while maintaining ease of manufacture
2Loss of energy
If phosphorescent materials with heavy metal complexes are used, then internal quantum efficiency reaches 100% by utilizing both singlet and triplet excitons, but the materials require precious metals like Ir and Pt and lack progress in blue light materials
Solution Approach 1:
The patent extracts and eliminates the heavy metal component from the phosphorescent material system, developing purely organic fluorescent materials that achieve TADF through molecular design with appropriate HOMO-LUMO offsets, thereby avoiding precious metals while maintaining high internal quantum efficiency
Solution Approach 2:
The patent replaces expensive heavy metal complexes with inexpensive organic fluorescent materials that can be synthesized from common precursors, creating a cost-effective alternative that achieves comparable or superior performance without relying on scarce resources
3Loss of energy
If TADF materials are synthesized to have lower singlet-triplet energy difference for fast reverse intersystem crossing, then internal quantum efficiency improves, but the spectral coverage from blue-green to orange-red light is not achieved
Solution Approach 1:
The patent segments the broad spectral range into distinct emission regions by designing separate fluorescent TADF materials with specific donor-acceptor combinations tailored for blue-green emission (450-550 nm) and orange-red emission (600-700 nm), each optimized for fast reverse intersystem crossing in its respective spectral region
Solution Approach 2:
The patent develops a universal molecular design platform using various electron donor and electron acceptor units that can be combined to achieve both fast reverse intersystem crossing and tunable emission wavelengths across the blue-green to orange-red spectrum, making the material system adaptable for multiple applications
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 synthesized material enables OLEDs with high luminous efficiency and broad spectral coverage, improving the performance and application prospects of OLEDs by effectively utilizing both singlet and triplet excitons, and is confirmed through nuclear magnetic resonance and mass spectroscopy.
Implementation Method 1
the triplet excitons can return to the singlet state by the reverse intersystem crossing (RISC), and then emit light when transiting to the ground state by radiation
Implementation Method 2
pure organic thermally activated delayed fluorescence (TADF) materials are cleverly synthesized to have lower singlet-triplet energy difference (ΔEST), such that the triplet excitons can return to the singlet state by the reverse intersystem crossing (RISC)
Implementation Method 3
emit light when transiting to the ground state by radiation
Implementation Method 4
high photoluminescence quantum yield (PLQY) are required for manufacturing a highly efficient OLED
Data Source
AI summary
An efficient blue-green to orange-red thermally activated delayed fluorescence material, a manufacture method, and an application thereof are provided. This disclosure solves the technical problems in the art by cleverly synthesizing a series of thermally activated delayed fluorescence materials, which have lower singlet-triplet energy difference, high luminous efficiency, and fast reverse intersystem crossing constant, and simultaneously fine-tuning the structure to cover the spectrum from blue-green light to orange-red light. Further, their structures are confirmed by nuclear magnetic resonance and mass spectroscopy, and their photophysical properties are also determined. Therefore, these luminescent thermally activated delayed fluorescence (TADF) materials are applied to light-emitting layer for manufacturing a series of organic light-emitting diodes (OLEDs) having high performance, which have great application prospects and economic value.