B-N Electroluminescent Material Structure for Lower OLED Efficiency Roll-Off
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Solution Overview
Problem
Current organic light-emitting diode (OLED) materials face challenges in achieving high luminous efficiency, long service life, and color purity due to the limitations of fluorescent, phosphorescent, and thermally activated delayed fluorescence (TADF) materials, particularly in blue light emission, which are costly and suffer from stability and efficiency issues.
Innovation Solution
An organic electroluminescent material with a B—N structure is developed, incorporating a dimethyl-substituted methylene group to form a rigid structure, reducing non-radiative vibrations and fluorescence quenching, and introducing asymmetry to enhance efficiency and reduce film aggregation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If phosphorescent materials are used for green and red light emission, then internal quantum efficiency can reach 100%, but the materials contain heavy metals causing high cost and poor stability
Solution Approach 1:
The patent changes the material composition parameters by replacing phosphorescent materials containing heavy metals with TADF materials that utilize triplet excitons through reverse intersystem crossing, achieving high efficiency without heavy metals. The molecular structure parameters are optimized by adjusting the dimethyl-substituted methylene group configuration to control non-radiative decay rates and improve stability.
Solution Approach 2:
The patent employs organic TADF materials that are free from expensive heavy metal components, using instead lightweight carbon-based molecular structures with carefully designed HOMO-LUMO energy levels to achieve comparable or superior performance at lower cost and improved environmental compatibility.
2Use of energy by moving object
If TADF materials are used to achieve 100% internal quantum efficiency, then triplet excitons can be transformed into singlet excitons, but the materials have strong charge transfer characteristic and too wide full-width at half maximum which is not conducive to high color purity display
Solution Approach 1:
The patent applies local quality by designing specific molecular regions with distinct functions: the B-N resonance structure core provides the necessary charge transfer for TADF, while the attached aromatic rings and dimethyl-substituted methylene groups locally modify the HOMO-LUMO energy gap to control emission wavelength and narrow the FWHM, achieving both high efficiency and color purity.
Solution Approach 2:
The patent introduces asymmetry through the dimethyl-substituted methylene group configuration, which distorts the molecular symmetry to reduce non-radiative decay pathways and control the vibrational coupling, thereby narrowing the emission bandwidth and improving color purity while maintaining high internal quantum efficiency.
3Device complexity
If blue light materials are fluorescent materials that can only use singlet excitons for light-emission, then the structure is simple, but the theoretical efficiency is only 40% which is far below the market demand
Solution Approach 1:
The patent changes the energy level parameters by designing TADF materials with optimized singlet-triplet energy gap (ΔEST) to enable efficient reverse intersystem crossing, allowing triplet excitons to be converted into singlet excitons for light emission, thereby achieving near 100% internal quantum efficiency while maintaining relatively simple molecular structures.
4Stability of the object's composition
If a conventional B—N resonance structure is used, then the structure is stable, but non-radiative vibration occurs and delayed fluorescence lifetime is long causing efficiency roll-off
Solution Approach 1:
The patent creates a composite molecular structure combining the stable B-N resonance core with attached aromatic ring systems and dimethyl-substituted methylene groups. This composite structure maintains the structural stability of the B-N unit while the attached groups provide rigidification that suppresses non-radiative vibrations and reduces efficiency roll-off through enhanced molecular rigidity.
Solution Approach 2:
The patent introduces structural curvature through the dimethyl-substituted methylene group configuration, which creates a three-dimensional rigid structure that reduces molecular planarity and thereby decreases non-radiative decay pathways while maintaining the stability of the B-N resonance core, leading to improved luminescence efficiency and reduced efficiency roll-off.
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 B—N structure material achieves high efficiency and reduced efficiency roll-off, improving the performance of OLED devices by enhancing luminous efficiency and stability, particularly in blue light emission.
Implementation Method 1
Organic light-emitting diode (OLED) devices... holes and electrons recombine in the emission layer to generate excitons. These excitons transition from the excited state to the ground state, thereby emitting visible light.
Implementation Method 2
Based on a conventional B—N resonance structure, in such materials, an aromatic ring that does not participate in the resonance is fixed to a resonance ring by means of a dimethyl-substituted methylene group
Implementation Method 3
the introduction of the dimethyl-substituted methylene distorts the B—N planar skeleton, which can reduce fluorescence quenching at high concentrations
Implementation Method 4
an aromatic ring that does not participate in the resonance is fixed to a resonance ring by means of a dimethyl-substituted methylene group to form a larger rigid structure, thereby decreasing non-radiative vibration
Data Source
AI summary
The present disclosure relates to an organic electroluminescent material having a structural formula as shown in formula (A) or (B). Based on a conventional B-N resonance structure, in such material, an aromatic ring that does not participate in the resonance is fixed to a resonance ring by means of a dimethyl-substituted methylene group to form a larger rigid structure, thereby decreasing non-radiative vibration, reducing delayed fluorescence lifetime and reducing efficiency roll-off. Moreover, the introduction of the dimethyl-substituted methylene distorts the B-N planar skeleton, which can reduce fluorescence quenching at high concentrations, thereby obtaining relatively high efficiency. In addition, when Cy1 and Cy2 are different, especially after a heteroatom is introduced, this type of asymmetric structure can further distort the molecular plane, reduce film aggregation and quenching, and achieve a higher current efficiency.