Organic Electroluminescent Device with Narrow Blue Emission
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Solution Overview
Problem
Current organic electroluminescent devices face challenges in achieving efficient energy transport and emission, particularly in the blue region of the visible light spectrum, with limited lifespans and suboptimal optical properties when using combinations of triplet-triplet annihilation, thermally activated delayed fluorescence, and near-range charge transfer materials.
Innovation Solution
An organic electroluminescent device with a light-emitting layer comprising a triplet-triplet annihilation material, a thermally activated delayed fluorescence material, and a near-range charge transfer emitter, where the energy levels are optimized to ensure efficient energy transfer and emission with a narrow full width at half maximum, primarily emitting in the blue region.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If a TADF material is combined with another compound having lower S1 energy, then energy transport efficiency is improved, but emission spectrum broadening occurs and device lifespan is reduced
Solution Approach 1:
The patent applies parameter changes by precisely controlling the energy level relationships between materials. Specifically, the TADF material is designed with S1 energy 2.7-3.2 eV and T1 energy 2.2-2.7 eV, while the NRCT emitter has S1 energy 2.4-2.9 eV. This optimized energy parameter configuration enables efficient energy transfer while preventing excessive broadening of emission spectrum and degradation of device lifespan.
Solution Approach 2:
The patent employs composite materials by combining TADF materials with NRCT emitter materials in a light-emitting layer. This composite approach leverages the complementary properties of both materials: the TADF material provides efficient energy transport and the NRCT emitter delivers narrow emission with high quantum yield, achieving synergistic improvement in both energy efficiency and device stability.
2Illumination intensity
If high energy photons are used to achieve blue emission, then emission wavelength is improved, but material degradation accelerates due to exceeding bond dissociation energy
Solution Approach 1:
The patent introduces an intermediary approach by using TADF materials as energy mediators. The TADF material absorbs high energy and transfers it to the NRCT emitter through triplet-triplet annihilation, avoiding direct excitation of the NRCT emitter with high energy photons that would cause bond dissociation. This intermediary energy transfer mechanism protects the NRCT emitter from degradation while maintaining blue emission.
Solution Approach 2:
The patent converts the potentially harmful high energy photons into beneficial effects through triplet-triplet annihilation. Instead of allowing high energy photons to directly damage the NRCT emitter, the system uses TADF materials to absorb this energy and convert it into triplet excitons, which then transfer energy to the NRCT emitter in a controlled manner, transforming a harmful factor into a useful energy transfer mechanism.
3Use of energy by moving object
If multiple emitter materials are combined in a single layer, then energy transport efficiency is improved, but device complexity increases
Solution Approach 1:
The patent applies local quality by assigning specific functional roles to different materials within the light-emitting layer. The TADF material is specifically designed with certain energy level characteristics (S1: 2.7-3.2 eV, T1: 2.2-2.7 eV) for energy transport, while the NRCT emitter is selected with complementary properties (S1: 2.4-2.9 eV) for narrow emission. This localized functional assignment simplifies the overall system design despite using multiple materials.
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 combination results in an organic electroluminescent device with improved quantum yields, extended lifespan, and desirable blue emission characteristics, overcoming previous limitations in optical properties and device longevity.
Implementation Method 1
A central element of an organic electroluminescent device for generating light is a light-emitting layer placed between an anode and a cathode... The decay of such excited states (e.g., singlet states such as S1 and/or triplet states such as T1) to the ground state (S0) desirably leads to light emission
Implementation Method 2
WO 2015/135624 teaches an OLED which comprises a TADF material in combination with a sterically shielded fluorescent compound
Implementation Method 3
an organic electroluminescent device according to the present invention... which exhibits a narrow - expressed by a small full width at half maximum (FWHM) - emission
Implementation Method 4
When a voltage (and current) is applied to an organic electroluminescent device, holes and electrons are injected from an anode and a cathode, respectively, to the light-emitting layer... Excitons of high energy are then generated by recombination of the holes and the electrons
Data Source
Figure 1
AI summary
The present invention relates to organic electroluminescent devices comprising a light-emitting layer B comprising a triplet-triplet annihilation (TTA) material, a thermally activated delayed fluorescence (TADF) material and a near-range-charge-transfer (NRCT) emitter material, which exhibits a narrow - expressed by a small full width at half maximum (FWHM) - emission. Further, the present invention relates to a method for obtaining a desired light spectrum and achieving suitable (long) lifespans of an organic electroluminescent device according to the present invention.